Telluride and the San Juan Mountains in southwest Colorado in January 2025. About one mile of relief separates the town and the highest mountaintops. Photo by Mitch Tobin.
Sometimes snow falls when the air temperature is warmer than water’s freezing point of 32° Fahrenheit.
Figuring out the dividing line between rain and snow has long flummoxed forecasters, especially in places like the high country of the American West, where complex topography and dramatic elevation differences shape the weather.
The fuzziness of the boundary can have life-or-death implications.
If rain falls on top of snow, that can cause disastrous flooding.
“We saw that in Yellowstone in 2022,” said Meghan Collins, associate research scientist at the nonprofit Desert Research Institute. “There was a really large snowpack in the Northern Rockies, forecasters called for snow, and it came as rain and it washed out roads, it washed out bridges and it washed out houses.”
Meteorologists and transportation officials want to know if roads are being coated with rain or snow so they can alert the public and deploy snowplows.
Avalanche experts care about the type of precipitation because that can be a pivotal factor in predicting the risks facing people recreating in the backcountry.
As climate change shifts snowflakes to raindrops, a better understanding of the dividing line between rain and snow is also of interest to water managers, ecologists and others who monitor streams and rivers that support both ecosystems and economies.
To gain a clearer picture of the rain-snow transition and its impact on the water cycle, scientists have been using a free phone app and data from thousands of volunteer observers who provide real-time reports of what precipitation type they’re seeing.
The observations from the NASA-funded citizen science project—known as Mountain Rain or Snow—have highlighted the shortcomings of existing approaches to differentiating the phases of precipitation, according to a study published in Geophysical Research Letters in December.
“It’s very hard for weather monitoring technologies to estimate rain versus snow without ground-based observations, and so this project is seeking to fill a gap that has connections to multiple fields,” said Collins, a co-author of the study who works on the crowdsourcing project.
So why might it be snowing when the temperature is several degrees above 32?
“This is not a change to the law of physics, but it does point to the complexity of our atmosphere,” Collins said. “Snow forms in layers of the atmosphere that are colder than where we live, work, and play.”
On the way to the ground, the snowflakes may persist while passing through warmer layers. Humidity levels play a key role in determining the rain-snow threshold. In relatively dry, continental conditions, such as in the Rocky Mountains, there are fewer water vapor molecules in the atmosphere, so the melting of snowflakes is slower, preserving them longer.
Crowdsourcing precipitation data
The project, which began in the Sierra Nevada in January 2020, relies on nearly 2,000 observers who have submitted more than 85,000 observations of precipitation as of December 2024 (see bottom of post for how to sign up).
Volunteers are asked to use an app to record whether they’re seeing snow, rain or mixed precipitation. The app records the time and location, using the device’s Global Positioning System, then transmits the data for processing.
A screenshot of the web-based reporting app.
There’s no need for observers to record the temperature. That information comes from the nation’s extensive network of weather sensors, plus some complex modeling that fills in the intervening areas with temperature data.
“We ask observers to send us observations whenever they see precipitation start or change type,” Collins said. “It’s those transitions between rain, snow and that wintry mix that we’re really interested in, especially around the freezing point.”
NASA’s interest in the project stems from its Global Precipitation Measurement Mission, a constellation of satellites that tracks weather via remote sensing and uses algorithms to determine if it’s raining or snowing.
The project helps NASA understand “where the satellite mission does well in estimating precipitation phase and where it struggles,” Collins said.
The December research paper used 39,680 observations from volunteers from January 2020 to July 2023 to assess three forecast products that distinguish between rain and snow.
“All products performed poorly in detecting subfreezing rainfall and snowfall above 2°C,” according to the study. “Crowdsourced data could help enhance methods used to determine precipitation phases and improve real-time weather forecasts.”
The study noted that previous research has revealed difficulties in determining what type of precipitation is falling from about 0°C to 4° Celsius (32° to 39.2° Fahrenheit).
“Unlike commonly used methods for determining precipitation phases, crowdsourcing visual observations of precipitation phases provides an effective and accurate way to monitor rain and snow patterns,” the paper concluded.
A flow chart helps volunteer observers decide how to submit an observation.
Informing forecasts
Raindrops and snowflakes are both made of water, but whether one or the other falls makes a big difference to water managers. A snowflake might remain up in the snowpack for months, while a raindrop might quickly run toward a river. A better understanding of the rain-snow threshold can inform the accounting of water planning efforts that hinge on the annual runoff season.
“If we know that there’s going to be more snow coming down, then we know better how much water we have in our snowpack, which is good for water balances and water budgets for the next water year,” said Nayoung Hur, another co-author of the study and a water resources engineer at Lynker, a science, engineering, and technology company. “How much streamflow are we going to have? What’s the peak runoff going to be? Are we going to have enough groundwater recharge for areas that rely on groundwater for their drinking water source or just water source?”
Another potential benefit of the project is informing avalanche forecasts.
“To the extent that what they’re doing improves the weather forecast, it’s massively helpful to us,” said David Reichel, executive director of the Sierra Avalanche Center, which provides forecasts for the greater Lake Tahoe area. “Precipitation is a major driver of avalanches, and so understanding if you’re going to get a foot of snow or an inch of rain or six inches of snow and then a half inch of rain—this part of the weather forecast is really influential on the avalanche forecast and what avalanche problems we’re likely to expect.”
One challenge is that the avalanche center publishes its forecasts early in the morning, but very few people are submitting real-time observations in the wee hours when it’s still dark out.
Rain-on-snow events can increase the avalanche danger by adding weight and infiltrating into the snowpack.
“Water in the form of rain is heavy, and even a little bit on a winter snowpack will significantly increase the avalanche danger,” Reichel said.
The Mountain Rain or Snow project is helpful to a variety of users, but it confronts a number of obstacles due to the complexity of mountain weather. For example, while computer models can provide high-resolution estimates of the temperatures where observations are recorded, those figures are not without errors since there are only so many weather stations out there.
Another challenge, Hur said, is that “a lot of people end up submitting their observations where it’s most comfortable,” such as from home, so there’s a comparative lack of data from places like the backcountry and mountaintops.
Even so, the extensive network of observers provides useful data and the scientists involved in the project say they’re impressed by the volunteers’ dedication. When the project ran a photo contest, it received 177 submissions from the field.
“Our observers are amazing,” Collins said. “There’s just a lot of talent and motivation in the community.”
Sign up to receive storm alerts via text: using the table below, find your region’s keyword and text it to 855-909-0798. You’ll receive a link to the web-based app.
Sleepy Bear Mobile Home Park resident Renee Hoffman washes dishes at her kitchen sink on January 21, 2025. After learning that her neighborhood water system is contaminated with PFAS, Hoffman started to distrust her tap and stopped using tap water for most household purposes. After washing the dishes, she carefully wipes them down, out of an abundance of caution. (Rae Solomon/KUNC)
Renee Hoffman was never thrilled about the water quality at her house in Sleepy Bear Mobile Home Park on the outskirts of Steamboat Springs.
“It just didn’t taste great,” she said. “It had that kind of calcium buildup and stuff.”
But one day in 2023, she got a letter from the mobile home park management that made her distrust her tap in a whole new way.
“This drinking water notice came through, telling us that there was PFAS in the water,” she said.
Polyfluoroalkyl Substances, or PFAS, are a class of compounds sometimes called “forever chemicals” because they don’t break down naturally in the environment.
“PFAS are ubiquitous,” said Zach Schafer, director for policy at the Environmental Protection Agency’s Office of Water. “They’re used in countless products that we use every day, whether it’s nonstick cookware or waterproof clothing. It’s used in stain resistant carpets. It’s used in firefighting foam. And it’s very useful, which is why it’s been used since the 1940s.”
But PFAS are also very harmful. Exposure to even a small amount of some PFAS compounds, like Perfluorooctanoic acid, or PFOA, and Perfluorooctanesulfonic acid, or PFOS, can disrupt immune response, liver and thyroid function and cause heart disease and cancer. They can also affect developing fetuses.
“We’re increasingly learning that some PFAS that we’ve studied a great deal have pretty serious adverse health effects at very, very low levels,” Schafer said. “Based on the latest science, there really is no safe level in drinking water.”
The notice that Hoffman received included information from the Colorado Department of Public Health and Environment informing her that the shallow water well supplying her small neighborhood had tested positive for PFOA and PFOS and warning about the potential health impacts of exposure.
“I almost threw it out,” she said. “But I’m glad I opened it, because I wouldn’t have heard of it any other way.”
The shallow well at the Sleepy Bear Mobile Home Park on the western edge of Steamboat Springs sources water from the Yampa River to supply the 54-lot neighborhood. The water system tested positive for PFAS in 2023. (Rae Solomon/KUNC)
The letter offered some recommendations for reducing exposure but stopped short of telling residents to stop drinking their tap water, “as current health advisories are based on a lifetime of exposure.”
That did little to reassure Hoffman that the water was safe for her family.
“We stopped giving it to our animals, stopped using it to cook noodles and things like that. We just stopped using it altogether,” she said.
New drinking water standards
Last year, the EPA created new drinking waterstandards that limit PFOA and PFOS to less than 4 parts per trillion, which is the smallest concentration tests can reliably detect. But PFAS have already worked their way from industrial sources into drinking supplies across the country. The EPA estimates between 6 and 10 percent of the nation’s utilities are contaminated. They have until 2029 to fix the problem.
“We are going to save thousands of lives, prevent tens of thousands of avoidable illnesses, and reduce the levels of PFAS in more than 100 million people’s drinking water nationwide,” Schafer said.
The new rules will require all water systems across the country to start monitoring PFAS by 2027. But some states are ahead of the curve. The Colorado Department of Public Health and Environment launched a free, voluntary testing program in 2020 and state officials report that so far, about two-thirds of the state’s water utilities have opted in.
Through that program, the state has already identified 29 water systems, in communities large and small, with a PFAS problem that needs to be addressed.
For the most part, the point of contamination remains a mystery and public health officials are more focused on removing the chemicals than discovering their source.
“Rarely can we trace the levels we detect in drinking water back to specific sources of PFAS contamination,” a CDPHE representative wrote in an email. “Our focus is to help our public water systems assess PFAS levels in their drinking water and reduce exposure.”
The good news, according to Schafer, is that the technology to remove PFAS from drinking water already exists and is readily available.
“Those include activated carbon ion exchange and reverse osmosis,” he said.
But for some utilities, it might make more sense to reduce their reliance on or to simply stop using a contaminated water source.
“Depending on the specific characteristics, the size and the needs of a water system, they can choose how to meet the standard,” Schafer said. “It’s going to vary based on what PFAS are in their water, at what levels, and what the design of the water treatment system already is. So, it really isn’t going to be a one-size-fits-all approach.”
Costly fixes for small water systems
No matter the approach, dealing with PFAS contamination is bound to be a major undertaking. According to John DeGour, regulatory affairs specialist with the National Rural Water Association, smaller communities are likely to find it a struggle.
“You have to pay for sampling, you have to install treatment if necessary, or find a new source,” he said. “But if you’re a small system, you obviously have less resources to do that.”
When PFAS turned up in one of the wells supplying rural Keenesburg, on Colorado’s Eastern Plains, public works director Mark Gray was surprised.
Well 11, one of several wells supplying water to rural Keenesburg, Colo. from the Lost Creek Alluvial, first tested positive for PFAS contamination in 2019. The small water system serving about 860 users has until 2029 to reduce PFAS levels to new federal standards adopted last year. (Rae Solomon/KUNC)
“I never anticipated us to have any PFAS in our wells,” he said. “It’s the biggest problem we have. It’s the only problem we have.”
His first instinct was to look for ways to pay for potentially expensive fixes.
“We have made applications to every grant available — grants for engineering, grants to build filtration. We are very actively looking at everything that’s available to us,” Gray said.
Congress set aside billions in the Bipartisan Infrastructure Law of 2021 to address PFAS in drinking water. That includes $6 billion specifically for small and disadvantaged communities. According to the CDPHE, Colorado has already received $31 million out of a promised $189 million for PFAS remediation. But with a cloud of uncertainty over how the new Trump administration plans to dole out federal funds, it’s suddenly unclear whether and when the balance will ever reach its intended users.
It’s still too soon to know which PFAS removal approach will be right for Keenesburg, or what the price tag will be. And while any grant funding that is made available can help cover the initial costs, utilities will ultimately be on the hook for the cost of ongoing operations.
“We’re being tasked from the EPA to try to come up with an almost impossible standard,” Gray said. “You almost have to anticipate the increased cost in treatment.”
Those increased costs will likely raise the rate that consumers pay for water. But utilities will have little choice.
“We’re a small town and we’re one of the few communities that provides its own water,” Gray said. “We want it to be safe.”
As for the Sleepy Bear Mobile Home Park, the easiest solution just might be to abandon the neighborhood well altogether and tap into the municipal system in Steamboat Springs.
Renee Hoffman no longer gives her dog and cats tap water after learning that the local water system contains PFAS. Now she hauls in extra filtered water from a private treatment plant down the road. (Rae Solomon/KUNC)
“We support that and we want to work with Sleepy Bear to make that happen,” said Steamboat Springs water distribution and collection manager Michelle Carr. “It’s really just a matter of figuring out the logistics.”
Those logistics would have to include extending the city water main westward, a project Carr said the city has already planned and budgeted for as they eye future developments on the city’s western edge.
But even that could come at “significant cost,” according to Thomas Morgan, manager of KTH Enterprises, which owns Sleepy Bear Mobile Home Park. Via text message, he wrote that he has been meeting with city officials, “to see if costs and requirements could be lessened.”
Indeed, there might be some appetite among city council members to subsidize a connection to the city water system for the mobile home park, “because of their interest in supporting affordable and low-income housing,” Carr said.
But from resident Renee Hoffman’s perspective, the park management needs to make clean water a priority, whether or not those subsidies come through.
”There’s a lot of young kids here,” She said. “To think that they were drinking that water from infancy — what levels they might have in their bodies.”
And she just wants her family to be able to do normal things again, like brush their teeth and wash the dishes without worrying that the water could make them sick.
“Nobody wants their rent to be raised, right?” she said. “But if we were to secure a better water source for our long-term health, I think you just have to weigh the benefits of it and ante up, I guess.”
This story was produced by KUNC, in partnership with The Water Desk at the University of Colorado’s Center for Environmental Journalism.
Buckeye, Arizona, has plans to become one of the Southwest’s largest cities in the next decades. (Brett Walton/Circle of Blue)
BUCKEYE, Ariz. – Beneath the exhausting Sonoran sun, an hour’s drive west of Phoenix, heavy machines are methodically scraping the desert bare.
Where mesquite and saguaro once stood, the former Douglas Ranch is being graded and platted in the first phase of a national real estate developer’s gargantuan plan that foresees, in the next few decades, as many as 100,000 new homes to shelter 300,000 people. In late October 2024, dozens of trees, salvaged from the land and potted as if they had just arrived from the nursery, watched over the quiet construction zone.
This remote site in western Maricopa County, between the stark White Tank Mountains and frequently dry Hassayampa River, is the location of Teravalis, the largest master planned community in Arizona and one of the largest in the country. It is part of a constellation of roughly two dozen master planned communities in the area – with names like Tartesso, Festival Ranch, Sun City Festival, and Sun Valley – that could propel upstart Buckeye in the coming decades to one of the largest cities in the Southwest. Buckeye planning documents anticipate a city population later this century between 1 million to 1.5 million if all the master planned communities are fully built out.
The Phoenix metro area is expanding ever outward, riding the decades-long wave of a nationwide redistribution of people toward warmer, sunnier states. That population growth – the state added nearly 1.2 million people in the last 15 years – has driven up home prices and pushed single-family home buyers into lands farther removed from the center. Buckeye is about as far removed as it currently gets.
All the while, the state’s water supply has declined. The Colorado River, shrinking due to a warming climate, has been in shortage condition since 2022, a situation that has cut Arizona’s allocation from the river by at least 18% annually. Groundwater, which has nurtured Buckeye to this point, is no longer sufficient for new growth in the area, the state says. Arizona Department of Water Resources decisions in 2023 about groundwater availability in the region sent shockwaves through the housing industry, halting new subdivisions in Buckeye and certain other locations around Phoenix that would have used local groundwater. The decisions affected only proposed developments that had not yet received permits to pump groundwater.
“We’re in an era of limits,” Tom Buschatzke, director of the Arizona Department of Water Resources, reiterated during a January 16, 2025, meeting to discuss new policies that could unlock homebuilding in the area. The Arizona Municipal Water Users Association echoed that sentiment weeks earlier: “Arizona’s future is not secure if we continue to depend only on groundwater.”
The Home Builders Association of Central Arizona, an influential trade group, reckons that 200,000 homes in the greater Phoenix area for which builders thought they had sufficient water are now in limbo. On January 22, 2025, the association announced a lawsuit against the state over its restrictions on groundwater use that have held up home construction.
Howard Hughes Holdings, the national real estate company that is developing the 37,000-acre Teravalis site, has secured water for only the first 8,500 homes, some of which are scheduled to be ready by next year. Where will the rest of the water come from? Deals could be made with nearby tribal nations to lease their senior rights. Ag land could be bulldozed and the water given over to housing. Wastewater can be cleaned up and reused. Groundwater could be pumped from designated “transport” basins from which water can be moved outside its natural watershed. Many options are on the table – even a farfetched pipeline carrying desalinated water from Mexico – but they require delicate political negotiation, wads of money, or both.
The exurban growth is a clash between Old Arizona, with its cotton fields and cattle ranches, and New Arizona’s subdivisions and silicon chip manufacturers. In Buckeye, the two eras often occupy adjacent parcels, each representing different ways of irrigating the Arizona Dream. Behind all the political maneuvering is one overriding question: How should Arizona’s limited water be used?
Growing Pains
Until this century, Buckeye was a tiny farm town known for its cotton fields and rodeo. Its story since then has been one of audacious growth. In the last 25 years, the number of residents has climbed from roughly 8,000 to now almost 120,000. And that’s just the start.
The Buckeye Planning Area, designated by the city, encompasses 639 square miles. Phoenix, by comparison, spreads across 519 square miles. Not all of the Planning Area is within the current Buckeye city limits, but city officials do anticipate that those lands, prior to development, will be incorporated in order for them to access city services. At present, just 15% of the Planning Area is developed and the city boundaries are a patchwork of annexations.
“Water and infrastructure are really the two most significant challenges I think that we have moving forward,” said Eric Orsborn, mayor of Buckeye.
Orsborn, an enthusiastic municipal booster who owns a construction business, knows the importance of the homebuilders. “You’re the fuel that helps us grow,” Orsborn told a representative from the Home Builders Association of Central Arizona at a Buckeye City Council meeting on October 15, 2024.
Because of its farming history, Buckeye is latticed with irrigation canals. (Brett Walton/Circle of Blue)
To understand the current brouhaha over housing development, turn back the clock 45 years. At the time, groundwater extraction was so rampant that the land surface was sinking and wells were going dry. The state needed to rein in its use. Lawmakers did so through the Groundwater Management Act of 1980, which established four “active management areas,” or AMAs, in which groundwater would be regulated. Now there are seven AMAs. Municipalities in the AMAs could become “designated water providers” if they proved a 100-year renewable supply of water such as treated wastewater or a surface water source like the Salt River or Colorado River, which began to be delivered to the Phoenix area via the Central Arizona Project canal in 1985.
Buckeye, because it still relies almost exclusively on groundwater, is one of the few cities in the Phoenix AMA that is not a designated provider. This has consequences. The city’s three water providers pump groundwater and residents pay the Central Arizona Groundwater Replenishment District, a state-created agency, to recharge a portion of that pumping. Meanwhile, commercial and industrial users, which are not subjected to the same groundwater restrictions as residential customers, are allowed to build and pump without replenishment. The city has recently welcomed distribution centers from the retailers Five Below and Walmart. But Buckeye is not allowed to pump more groundwater to serve new outlying subdivisions. Instead, master planned communities like Teravalis that are located in an AMA are responsible for securing their own water and proving a 100-year renewable supply. This is called a certificate of assured water supply.
Until recently, local groundwater sufficed for these certificates. Howard Hughes will be using groundwater for Floreo, the 8,500-unit first phase of Teravalis that is now under construction. But at the moment water supply for the rest of the project and for other projects around it in the Hassayampa basin are in doubt because of a state determination in 2023 that local groundwater is insufficient and cannot be used for a certificate of assured water supply. The Home Builders Association of Central Arizona disputes the modeling that informed the decision, and filed a lawsuit on January 22 to reverse it.
In parallel, state lawmakers and water officials are attempting to promote workarounds that would appease homebuilders and cities like Buckeye and allow limited groundwater pumping in the short term, but also protect long-term groundwater sustainability in the AMAs.
One option, which has already been approved by the Gov. Katie Hobbs, provides places like Buckeye a way to become designated providers while still pumping groundwater in the interim. Buckeye leaders and representatives for the master planned communities initially objected to stipulations in the program that they felt required them to give up too much water for too little benefit. Nonetheless, Buckeye has now committed to applying for this ADAWS program.
The second consideration is a voluntary program to incentivize the conversion of farmland to housing. These discussions were initiated after Gov. Hobbs vetoed a bill on the topic last year because she felt the ideas needed more vetting. The intent is two-fold, said Tom Buschatzke of the Department of Water Resources: allow more housing to be built but also secure a long-term reduction in groundwater use by facilitating what has already been taking place in the state in the last century. The ag-to-urban concept would not help places like Teravalis, which is being built on desert land north of I-10, not former farmland. And there are still big unanswered questions about how much water could be given over to housing, how much would need to be replenished underground, which lands would qualify, and where the water could be used.
Billboards in Buckeye advertise new homes for sale. (Brett Walton/Circle of Blue)
Grady Gammage Jr., a lawyer at the Phoenix-based firm Gammage & Burnham who works at the intersection of real estate development and water supply, called the current groundwater situation a “logjam.” In his view, what’s needed is a compromise that allows for some groundwater use now with an assurance to build the expensive infrastructure to bring in an alternative water source down the road to fill the gap.
“One of the things that I think somebody needs to take the lead in thinking about is the big picture infrastructure solutions,” Gammage Jr. said.
Those discussions will take some time because state officials do not want to rush the process, said Patrick Adams, the governor’s water policy adviser. “We want there to be consensus, bipartisan work, and really rigorous analysis on these pretty impactful water policy program changes.”
Water-Efficient Designs
What gets built determines water use. New housing developments in Arizona require less water than their predecessors because of landscaping changes, said Spencer Kamps, vice president of legislative affairs for the Home Builders Association of Central Arizona. Xeriscaping – employing desert-native vegetation – is the norm, both through changes in code and changes in culture. To mimic a lawn aesthetic, some homes in new subdivisions have patches of artificial turf in front of the house. But turf grass is out.
Outdoor use is the biggest factor for a residential development’s water footprint. The dry desert air vacuums moisture from the ground and turf grass lawns are relatively thirsty embellishments. Terry Lowe, Buckeye water director, said that about 60% of the city’s residential water is used outdoors.
Many new developments in the state share a defining trait: they are built atop former farm fields. The replacement of crops with cul-de-sacs has helped moderate water use, which is less today than in the mid-1950s, when only a million people lived in the state.
Howard Hughes is pitching Teravalis as a continuation of this trend toward environmentally conscious development, though it is being built in the desert, not on formerly irrigated fields. A slide deck for investors notes the company’s intention to be “one of the leading sustainable MPCs in the nation with a strong focus on environmental awareness and innovative technology.” Its promotional materials advertise water-efficiency goals of 35% below the state average water use per person. There will be limits on pool size and covers required to reduce evaporation when not in use. Wastewater will be reclaimed and recycled for park irrigation. Howard Hughes representatives declined to be interviewed for this story or to respond to written questions about their water use and development plans.
Before sunrise in mid-October, roosters crow and nail guns can be heard in the distance. Construction workers are already at the job site on a day in which the temperature will exceed 100 Fahrenheit. (Brett Walton/Circle of Blue)
Achieving these goals requires help. Building decisions are a three-partner dance between developers, homebuilders, and municipalities. Developers like Howard Hughes are responsible for the big capital investments: buying land, acquiring water, and installing streets, sidewalks, and drainage. This is all the “horizontal” infrastructure.
Once these assets are in place, the “vertical” stage – homebuilding – can begin. Developers offer blocks of the platted land to established companies like Lennar, KB Home, Brightland, and Century Communities. These homebuilders follow local and state codes, as well as developer preferences, which can be stricter than code requires, Kamps said. In the case of Teravalis, Howard Hughes will set the water use goals and homebuilders will follow the lead.
That guidance from Howard Hughes is not yet available, according to one of the seven companies selected to build homes there. Jill Ebding of Courtland Communities said that Howard Hughes has not told them final water-efficiency design guidelines.
“We can submit a house plan with just four walls, a roof, and a foundation – here’s our floor plan,” Ebding said laughing. “But we haven’t set up anything with landscaping or anything additional like that.”
Will the designs in the Floreo phase of Teravalis be substantially different from what is already on the market? Ebding did not think so, at least not from Courtland Communities.
Road to Somewhere?
The road to Teravalis, at exit 109 from I-10, is named Sun Valley Parkway. Built by private investors in the late 1980s, the road was a lonely speculation that one day people would move here. Expected growth did not happen immediately. “It was like a road to nowhere that was great for biking, was great for truck driving schools going out and practicing and training,” Orsborn said about the parkway’s early years.
Teravalis, a project of Howard Hughes Holdings, a national real estate developer, envisions 100,000 homes in the desert north of Buckeye — if the company can find water for them. (Brett Walton/Circle of Blue)
Sun Valley is still, by and large, a lonely road. Tartesso is out this way, at the southern end, closest to central Buckeye. At the northern end, where the road loops east around the White Tank Mountains in the direction of Phoenix, is Sun City Festival. In the middle, miles from any habitation, is the blank slate of Teravalis and the outlines, in planning documents, of a half dozen other master planned communities. Gammage Jr. said that, due to the vagaries of real estate development, not all the housing units approved by the city will ultimately be built. But many will.
Such growth has been the history of Arizona since statehood: defying watershed limits while engineering solutions to fill the supply gap. Cities, meanwhile, have expanded farther into the desert and tapped increasingly distant water sources. New water sources will not be cheap water sources. Knowing this, Orsborn looks at future growth as a challenge to be met step by step.
“We don’t have to solve water for the entire 1 million people today,” Orsborn said. “We can do this incrementally and come up with the water needs for the next 10 to 20 years.”
If local groundwater is no longer available, the next chapter of growth in Buckeye will have to come from a creative alignment of finance, policy, technological innovation, and deal making – the New Arizona mix that sees a road in the desert and thinks it can lead somewhere.
Editor’s note: This article has been updated to reflect that Buckeye will apply for the state’s Alternative Designation of Assured Water Supply (ADAWS) program.
This story was produced by Circle of Blue, in partnership with The Water Desk at the University of Colorado Boulder’s Center for Environmental Journalism.
A USGS hydrologist uses a velocity rod to estimate streamflow as part of a project to develop methods for monitoring streamflow in remote headwater streams. (USGS)
Wyoming’s water chief wants emergency funds for hydrologists to measure flows in the state’s portion of the troubled Colorado River Basin, documentation he said is vital to preserving irrigation and other uses.
State Engineer Brandon Gebhart asked for $167,210 in supplemental budget funds, a piddling amount in the world of western water finances, but a critical sum necessary to launch the work this spring. He called parts of the proposed allocation an “emergency,” a designation that would enable disbursements to begin this fiscal year.
Among other things, the money would employ three full-time hydrographers to measure flows in the Green and Little Snake river drainages. The total figure covers money specifically directed toward Colorado River issues as Wyoming girds to protect irrigators and other water users.
Climate change and drought have upset basin flows and could upend allotments agreed to in the seven-state 1922 Colorado River Compact. That, in turn, could threaten Wyoming’s water rights.
“What we’re seeing is an increase [in] demand and a decrease in supply,” Gebhart told members of the Legislature’s Joint Appropriations Committee in December. “This likely means that our downstream states will have a greater interest in our water. Being a headwater state, it’s somewhat concerning.”
Upper basin states — Wyoming, Colorado, Utah and New Mexico — don’t agree with lower-basin users in Arizona, California and Nevada on how or whether to reapportion dwindling runoff that supports some 40 million people. Lower basin states want equal “one-for-one” cuts shared between the two divisions, Gebhart told irrigators last summer.
“Mandatory reductions are pretty much a hard ‘no’ for me,” a position shared across the upper division, Gebhart said.
Enhanced storage
“You’re not going to hear me in the press,” Gebhart told irrigators in Baggs last summer, but he’s outlined Wyoming and upper basin states’ position in several public meetings.
“We have less water than was ever anticipated when the compact originated,” Gebhart said. “The last 22 to 24 years are the driest, the least flow in that basin in over 1,000 years.”
The 1922 Colorado River Compact requires upper division states to allow 75 million acre-feet to flow past Lees Ferry, a gauging station just below Lake Powell’s Glen Canyon Dam, during a rolling 10-year span. Wyoming’s responsible for about 14% of that and, conversely, can use a similar percentage of what doesn’t run past the gauge.
Wyoming believes it hasn’t fully tapped its 1922 share and is pursuing three significant water storage projects to fulfill its rights. Those are at New Fork Lake, Fontenelle Reservoir and a proposed reservoir on the West Fork of Battle Creek above the Little Snake River.
Those plans would primarily increase water available to Wyoming irrigators and other users. Enhanced storage could also help fulfill Lees Ferry flow obligations, but Gebhart has made clear Wyoming is unwilling to contribute “more than what we’re already under obligation for in the compact,” unless that comes from conservation, including paid-for voluntary conservation.
Unlike the lower basin states that rely on Lake Mead, “we don’t have a large reservoir to supply our releases,” Gebhart said. Instead, Wyoming’s Colorado River Basin reservoirs provide only late-season irrigation, not years of backup.
“We’re dependent on whatever Mother Nature gives us [in] the run of the river,” Gebhart said. But, “the hydrology is drying out. We have less.
“We already suffer what they refer to as shortages,” he said. “Every year we go out, we regulate off users because there’s not enough water.”
The Fontenelle Reservoir stores water from the Green River in southwestern Wyoming, above the Flaming Gorge reservoir. (Ted Wood/The Water Desk)
Enhanced measurements
For Wyoming to protect its share, it needs to know how much water diverted from rivers makes it to agricultural fields. Without documentation that can withstand legal challenges, others might say Wyoming is consuming more water than it puts to beneficial use.
Beyond what water makes it to the alfalfa field, hydrologists could also document how much leaks from irrigation canals and flows back to the main waterway, thereby remaining in the system.
They can also measure how much of the water applied to fields eventually seeps back to a river or stream and down toward the lower basin. Rules of thumb that previously served water managers may not stand up in court.
For example, Wyoming has long operated its dam, reservoir and irrigation systems, assuming that half of the water applied to a field eventually rejoins the river as return flows. The state also acknowledges that up to 80% of the water running through a canal, depending on its construction and underlying geologic composition, can leak before arriving at its destination.
The amount of seepage and phreatophytic losses — canal-side, plant-used water — is an “area of agriculture data collection that need[s] to be updated and verified,” the U.S. Bureau of Reclamation said in 2022. Toward that end, Wyoming recently directed a study on canal loss from long and porous irrigation aqueducts.
More hydrographers and scientific measures would buttress Wyoming’s claims.
“We recognize that it is very tough for us to conserve a large amount of water,” Gebhart told irrigators last summer. A paid-for voluntary conservation program would allow the state to put water savings on a ledger. In Gebhart’s words, Wyoming would “stash it away in a federal facility with our name on it until it’s needed,” to satisfy 1922 compact requirements at Lees Ferry.
Although upper and lower basin states are at odds, Gebhart said it’s not too late to reach a consensus on how to operate the complex system before the federal government steps in and forces a compromise. Those negotiations, if they happen, are not going to be done in public, he said.
Despite his reluctance to make direct statements to the press, that “doesn’t mean that we’re not here,” Gebhart said.
This story was produced by WyoFile, in partnership with The Water Desk at the University of Colorado Boulder’s Center for Environmental Journalism.
Aerial view of the Sawatch Range in central Colorado on February 2, 2023. Photo by Mitch Tobin, The Water Desk.
I’ve been a generalist most of my career, sometimes even working as a “general assignment reporter,” so I frequently find myself trying to learn about new subjects and bodies of research.
After many self-imposed crash courses, I know that one of the most helpful steps is to understand the terminology used in an issue or field.
Snow science has been no exception, so as I’ve tried to educate myself about the West’s snowpack, I’ve encountered plenty of unfamiliar words and concepts—and realized that my understanding of some things was primitive or outright wrong.
To help me—and you—better understand snow, I’ve compiled a glossary below with definitions of key terms and explanations of important concepts. I begin with an overview of snow and the hydrologic cycle, then explain words and terms in alphabetical order.
I’ve drawn on several other existing glossaries and resources that I’ve listed at the bottom of this post.
It all begins with snowflakes, which are formed in the atmosphere when water vapor in the air condenses into ice crystals around a particle, such as dust. As they fall, snowflakes may grow complex patterns that are determined by temperature and humidity.
Snow is one of several types of frozen precipitation, and there’s a difference between snowflakes and snow crystals. As Ken Libbrecht, a CalTech physics professor and one of the world’s leading experts on snowflakes, explains:
“When people say snowflake, they often mean snow crystal. The latter is a single crystal of ice, within which the water molecules are all lined up in a precise hexagonal array. Snow crystals display that characteristic six-fold symmetry we are all familiar with . . . A snowflake, on the other hand, is a more general term. It can mean an individual snow crystal, but it can also mean just about anything that falls from the winter clouds. Often hundreds or even thousands of snow crystals collide and stick together in mid-air as they fall, forming flimsy puff-balls we call snowflakes. Calling a snow crystal a snowflake is fine, like calling a tulip a flower.”
A freezing cloud laden with moisture is a prerequisite for snowflakes, but so are the tiny particles, known as nuclei, upon which the water will freeze. The gist of cloud seeding, a technology meant to boost snowfall, involves creating more nuclei in clouds by shooting chemicals, such as silver iodide and dry ice, into the atmosphere.
Once a snow crystal is born, it grows as more water vapor condenses through two main processes: faceting and branching.
Not every storm will produce a menagerie of iconic crystals on your ski pants with those dendritic, radiating formations worthy of a holiday card. In fact, scientists like Libbrecht have come up with dozens of categories to describe the diversity of shapes. The graphic below, from Libbrecht’s SnowCrystals.com, shows his classification scheme.
The different shapes are due to varying conditions in the atmosphere when the flake forms and grows, which is summarized in Libbrecht’s diagram below.
Snow crystal morphology diagram. Source: Ken Libbrecht, SnowCrystals.com.
The horizontal axis at the bottom shows the temperature, while the vertical axis on the left is a measure of humidity known as supersaturation. These two factors—temperature and humidity—are different in every weather system and can change dramatically on a snowflake’s tumble through the sky.
The science behind the graphic above, known as a snow crystal morphology diagram, was “discovered in the 1930s by Japanese physicist Ukichiro Nakaya and his collaborators,” according to Libbrecht. The diagram below is a classification by Nakaya, who is credited with creating the first artificial snowflake.
Ukichiro Nakaya’s categorization of snowflakes. Source: SnowCrystals.com.
“Nakaya used to say that snowflakes are like hieroglyphs from the clouds,” Libbrecht writes, “because you can infer the conditions in the clouds by examining the shapes of the falling snow crystals.”
Freezing rain, sleet and graupel
A precious, unique snow crystal high in the atmosphere may not survive in that state on its way to terra firma. As the flake falls, it may encounter warmer conditions that cause it to melt and turn into rain. Or the precipitation may be classified as the dreaded freezing rain if the drops turn to ice on cold surfaces at ground level. Another possibility is for the snow to melt on its way down, but then freeze again before reaching the ground, which is sleet. The graphic below from the National Weather Service summarizes how these types of precipitation differ.
There’s one more type of precipitation connected to snow worth mentioning. Graupel, which is also known as “soft hail” and “snow pellets,” begins as snow, but the flakes pick up an extra layer of moisture known as rime on their way to the ground as supercooled droplets adhere to the crystals.
Snow flurries. Light snow falling for short durations. No accumulation or light dusting is all that is expected.
Snow showers. Snow falling at varying intensities for brief periods of time. Some accumulation is possible.
Snow squalls. Brief, intense snow showers accompanied by strong, gusty winds. Accumulation may be significant. Snow squalls are best known in the Great Lakes Region.
Blowing snow. Wind-driven snow that reduces visibility and causes significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind.
Blizzards. Winds over 35 mph with snow and blowing snow, reducing visibility to one-quarter mile or less for at least three hours.
For blowing snow and blizzards, it doesn’t need to be actually snowing: the mobilization of snow on the ground can create treacherous conditions of low visibility.
Hydrologic cycle: precipitation, evaporation, transpiration, sublimation, runoff, and more!
After precipitation falls, where does it go? Let’s take a quick tour around the hydrologic cycle, also known as the water cycle. Evaporation, the process by which a liquid becomes a gas, is an important factor in snowpack dynamics, with higher temperatures due to climate change increasing the conversion of liquid water to water vapor.
Transpiration occurs when water is absorbed by plants and released as water vapor through pores in leaves. This key component of the hydrologic cycle, combined with evaporation, equals evapotranspiration. In the context of the snowpack and climate change, if areas are snow-free and expose plants for a longer period due to warming, that would increase the volume of water that plants transpire and potentially decrease the amount of water reaching streams and rivers.
Sublimation occurs when snow and ice transition directly from the solid to the vapor phase without going through the intermediate liquid phase. Hard to measure, sublimation can be a significant player in the snowpack’s dynamics. It’s influenced by temperature, humidity, winds and other factors.
Surface runoff refers to the portion of precipitation that flows over land, while runoff more broadly includes the water that infiltrates into the soil and discharges into streams and rivers.
Infiltration is how water on the surface becomes soil moisture below ground. This process is affected by soil type, land cover, topography and other factors. Existing levels of soil moisture determine how much water can be absorbed and how much will run off. Some water percolates down and recharges groundwateraquifers.
The “efficiency” of runoff is the fraction of annual precipitation that becomes runoff, rather than being lost through evapotranspiration and sublimation. Many factors impact runoff efficiency, including soil moisture, land cover and weather conditions.
Below are three graphics illustrating the water cycle, all from the U.S. Geological Survey.
Source: U.S. Geological Survey.
Glossary of snow-related terms
Accumulation and ablation
Accumulation is the process by which snow and ice are added to the snowpack or a glacier. Snowfall is obviously the most important form of accumulation for the snowpack, but there is also frost deposited from surrounding air, plus some other rarer forms of frozen precipitation, such as graupel, that may be occasionally thrown into the mix.
Ablation describes the loss of snow and ice from an area due to melting, evaporation, sublimation, wind and other factors. The ambient temperature, the amount of incoming solar radiation and the reflectivity (albedo) of the snowpack play major roles in determining ablation, which can be thought of as the opposite of accumulation. The ebb and flow of ablation and accumulation is what determines the status of the snowpack and the size of glaciers.
Albedo
Albedo is a measure of the fraction of solar energy that is reflected from a surface. It ranges from 0 to 1. Surfaces with very high albedo, such as snow and ice, reflect a large fraction of incoming sunlight, while those with low albedo, such as bare ground or open water, absorb most of the energy. Albedo is derived from the Latin word for white, albus.
The Earth’s overall albedo is 0.3, but fresh snow can be around 0.9, which is why you can get a nasty sunburn on the slopes in winter. The albedo values of various other materials are in the graphic below that I created using data from MOSAiC: Multidisciplinary Drifting Observatory for the Study of Arctic Climate.
Dust-on-snow events can dramatically decrease the albedo of the snowpack and hasten its melting. On a global scale, albedo plays an important role in climate regulation. The less ice there is on the planet, the more solar radiation is absorbed, leading to further warming. Conversely, an increasingly frosty planet reflects more and more sunlight, cooling the planet further, freezing more ice, and so on, which is what happened to the planet when it turned into “Snowball Earth” many hundreds of millions of years ago.
Atmospheric river
An atmospheric river (AR) is “a long, narrow, and transient corridor of strong horizontal water vapor transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone,” according to the American Meteorological Society’s Glossary of Meteorology. These plumes of moisture are sometimes likened to “rivers in the sky” because they transport so much water vapor from the tropics toward higher latitudes. ARs can be beneficial and bust droughts, but they can also be hazardous by causing deadly flooding and extreme winter storms.
When ARs are forced upward by mountains or other forces, the water vapor cools, condenses and precipitates, as shown in the graphic below. This NOAA figure says the amount of water vapor in a strong AR “is roughly equivalent to 7.5-15 times the average flow of water at the mouth of the Mississippi River.”
The AR Scale is based on two factors: the duration of the event and its “maximum vertically integrated water vapor transport,” a measure of its water content and the speed at which it’s moving. As shown in the graphic below, there are five categories, with the bottom two described as primarily beneficial.
These three terms all refer to an area of land where precipitation collects and drains off into a common outlet, such as a river or bay. These terms are often used interchangeably, but basin is the formal geographic unit that’s used to report snowpack figures. In the American West, some water projects use massive pumps, tunnels and canals to move significant volumes of water from one basin to another to supply water for farms and cities. These are known as transbasin diversions.
Bomb cyclone and bombogenesis
A bomb cyclone is a rapidly strengthening extratropical cyclone that has experienced a drop in atmospheric pressure of at least 24 millibars in 24 hours. These storms can cause very severe weather, including intense snowfall, high winds and flooding.“When a cyclone ‘bombs,’ or undergoes bombogenesis, this tells us that it has access to the optimal ingredients for strengthening, such as high amounts of heat, moisture and rising air,” writes Esther Mullens, Assistant Professor of Geography at the University of Florida. “Most cyclones don’t intensify rapidly in this way. Bomb cyclones put forecasters on high alert, because they can produce significant harmful impacts.”
The term was coined in 1980 by MIT meteorologists Frederick Sanders and John R. Gyakum. In 2018, Gyakum told The Washington Post the name “isn’t an exaggeration — these storms develop explosively and quickly.”
We often hear about bomb cyclones hitting the Eastern Seaboard, where they can draw on the relatively warm waters of the Gulf Stream. The January 4, 2017, satellite image below shows a classic bomb cyclone. This event was also described as a Nor’easter, a storm along the East Coast characterized by strong northeast winds and heavy precipitation, but not all nor’easters are bomb cyclones.
Source: NASA.
Bombogenesis can also occur in the middle of the country or along the West Coast, as shown by the satellite image below from January 1, 2023.
Satellite image of a bomb cyclone approaching the West Coast on January 4, 2023. Source: NASA
See this excellent video below from The New York Times for a visual explainer of bomb cyclones.
Cloud seeding
Cloud seeding is an artificial process of boosting precipitation by adding particles, typically silver iodide, to clouds in order to provide nuclei around which water droplets and snowflakes can form. The technology is used by a number of water providers and ski resorts in the West. A 2020 study in the Proceedings of the National Academy of Sciences that used radar and precipitation gauges found that “cloud seeding can boost snowfall across a wide area if the atmospheric conditions are favorable,” according to the National Science Foundation, which funded the research. Learn more about cloud seeding in this story from Water Desk grantee Jeremy Miller.
A National Science Foundation “Doppler on Wheels” at Packer John Mountain in Idaho. Photo by Josh Aikens
Cryosphere
The cryosphere encompasses all the frozen parts of the Earth’s surface: snow cover, glaciers, permafrost, sea ice, ice sheets, ice shelves, icebergs and river/lake ice. The cryosphere stores freshwater for more than 1 billion people and helps regulate the planet’s climate by reflecting sunlight (see albedo). The term derivesfrom the Greek word kryos, meaning “cold” or “frost.” The illustration below shows the cryosphere’s components.
Virtually all of the cryosphere is located near the poles, with the extra-polar regions containing only 0.5% of ice and snow by volume.
Nearly all of the snow-covered areas are located in the Northern Hemisphere, ranging from 47 million square kilometers in winter to just 7 million square kilometers in summer, as shown in the graphic below. At its maximum in winter, snow covers about one-half of the Northern Hemisphere’s land mass. “The areal extent of snow varies more rapidly and more dramatically than that of any other widely distributed material on Earth,” write Olav Slaymaker and Richard E.J. Kelly inThe Cryosphere and Global Environmental Change.
Nearly all of the snow-covered areas are located in the Northern Hemisphere, ranging from 47 million square kilometers in winter to just 7 million square kilometers in summer, as shown in the graphic below. At its maximum in winter, snow covers about one-half of the Northern Hemisphere’s land mass. “The areal extent of snow varies more rapidly and more dramatically than that of any other widely distributed material on Earth,” write Olav Slaymaker and Richard E.J. Kelly in The Cryosphere and Global Environmental Change.
The chart below breaks down the cryosphere’s components into four categories: snow cover, sea ice, permafrost and ice. This graphic includes components that appear during different seasons. While snow cover in the Northern Hemisphere blankets around 47 million square kilometers in January, snow cover in the Southern Hemisphere only amounts to about 4 million square kilometers in late July.
Climate change is already taking a toll on the cryosphere, and even more drastic reductions are projected in the decades ahead as the planet warms. Glaciers, sea ice, ice sheets, permafrost, river/lake ice and snow cover in the Northern Hemisphere are all in trouble. For a solid overview of the global impacts, see the Intergovernmental Panel on Climate Change’s “Special Report on the Ocean and Cryosphere in a Changing Climate.”
Dust-on-snow
Dust-on-snow is exactly what it sounds like: deposition of airborne dust on the snowpack. More generally, scientists talk about light-absorbing particles that alter the reflectivity of the snowpack. In places like Colorado, dust-on-snow events are a big deal because the darker material reduces the snow’s albedo and causes it to absorb more heat, accelerating melting. While some airborne dust is natural, research has found that dust levels have soared since the West was settled due to agriculture, roads, development and other factors. See the Colorado Dust-on-Snow Program from the Center for Snow and Avalanche Studies for more on the issue.
The West’s increasing dryness threatens to reinforce snow loss by increasing the amount of dust that lands on the snowpack, thereby accelerating its melting. As a result, the most recent National Climate Assessment (NCA5) cautions that “under increasing aridity, agricultural practices such as fallowing and grazing on rangelands will need careful management to avoid increased wind erosion and dust production from exposed soils.” Adding insult to injury, NCA5 warns that those soils will be more susceptible to blowing around because hotter summers will “degrade protective desert soil crusts formed by communities of algae, bacteria, lichens, fungi, or mosses.”
Dust covers the snowpack of the San Juan Mountains near Telluride, Colorado, in May 2023. Photo: Mitch Tobin/The Water Desk with aerial support by LightHawk.
Glaciers and glacial landforms
A glacier is a large, perennial mass of ice and snow that moves slowly downhill under the influence of gravity. A glacier will form if the accumulation of snow and ice exceeds their loss through ablation (via melting, evaporation, sublimation and other forces).
Glaciers around the globe are threatened by warming and are used as a barometer of climate change effects. The graphic below, from the U.S. Environmental Protection Agency, shows a precipitous decline in reference glaciers around the globe from 1956 to 2023.
The photographs below show how Alaska’s McCall Glacier changed from 1958 to 2023.
Past Ice Ages covered many of the West’s mountains in ice, and the current landscape still reflects these past glaciations, which both erode and deposit material. (At the height of the Last Glacial Maximum, around 20,000 years ago, about one-quarter of the Earth’s land area was covered by glaciers.)
The diagrams below show some common glacial landforms, followed by definitions of terms most relevant to the American West.
Source: National Park Service. The photo on the right shows Mount Conness in Yosemite National Park.Source: National Park Service. Diagram A shows common glacial landforms; B is a photo of McCarty Glacier in Alaska, C is Yalik Glacier in Alaska, and D shows common types of glacial deposits.
Glossary of glacier-related terms
Arête: sharp, narrow ridge formed between two cirques or glacial valleys
Cirque: bowl-shaped depression carved by a glacier at the head of a valley
Col: saddle-shaped pass between peaks formed by two glaciers on either side of a ridge
Comb: jagged ridge caused by glacial erosion
Crevasse: deep crack in a glacier’s surface caused by stresses from the ice’s movement
Drumlin: elongated hill of glacial sediment shaped by the flow of ice
Esker: long ridge of stratified sediment deposited by meltwater streams flowing beneath a glacier
Firn: snow that has been compacted and crystallized but not yet converted to glacial ice
Glacial erratic: rock or boulder transported by a glacier far from its origin
Glacial step: step-like formation caused by differential erosion in glacial valley
Hanging valley: a tributary valley at a higher elevation due to glacial erosion of the main valley that often includes a waterfall
Horn: pyramid-shaped peak formed by the erosion of at least three cirques
Kettle lake: depression formed by the melting of a block of ice in glacial outwash
Mass balance: the difference between the amount of snow/ice gained through accumulation and the volume of snow/ice lost through ablation (via melting and sublimation); glaciers grow due to a positive balance and shrink due to a negative balance
Moraines: deposits of glacial sediment, including terminal (at the toe of a glacier), lateral (along the sides of a glacier) and medial (when lateral moraines join at the intersection of glaciers)
Nunatak: a peak that protrudes above the surrounding glacier or ice sheet and is not covered by ice
Outwash plain/delta/fan: formation created by the deposition of sediment as meltwater flows out of a glacier and deposits sand/gravel in a spreading formation
Tarn: small mountain lake in a cirque
U-shaped Valley: a valley with a wide, relatively flat floor and steep sides, formed by the carving of a glacier (in contrast to a V-shaped valley caused by river erosion)
Where are glaciers in the West?
According to the Glaciers of the American West, an online resource by Portland State University researchers, there are 8,348 glaciers in eight Western states, not including Alaska, with the most by far in Washington. These glaciers and permanent icefields range from “rivers of ice on Mount Rainier that are over 8 km (5 mi.) long to tiny patches of ice in the Rocky Mountains not much larger than a city block,” according to the site.
The diagram below shows the general locations where glaciers are found in the American West (not all of the purple areas are perennially frozen!).
These are the two main ways that scientists study and monitor the snowpack (plus many other natural phenomena). In-situ measurement involves the direct collection of data at a location using instruments in the field. In the context of snow, in-situ data may be collected by hand or via the automated sensors of a SNOTEL station, such as snow pillows. In-situ data tends to be very detailed and high quality, but for manual measurements, data collection may be time/labor intensive, and with fixed SNOTEL stations, data is limited to a single point in a complex landscape.
Remote sensing refers to data collected from a distance through devices such as satellites, aircraft and drones. These platforms use radar, lidar and other technologies to detect electromagnetic radiation at various wavelengths to provide data on snow cover, snow water equivalent, albedo, temperature, snow grain size, vegetation health and other measures. Owing to their remote vantage, these technologies can scan vast areas to collect data, including places that would be difficult to access, but they tend to have much lower spatial resolution and accuracy compared to measurements taken on the ground by people and sensors.
The table below shows how different bands in the electromagnetic spectrum respond to various snowpack properties.
Lake effect snow
Lake effect snow occurs when cold air moves over relatively warm water in an unfrozen lake, causing heavy, localized snowfall downwind from the water body.
Satellite imagery from November 18, 2014, showing lake effect snow around the Great Lakes. Source: NASA Earth Observatory.
The phenomenon is best known for its effects around the Great Lakes, but a similar process also plays out in Utah around the Great Salt Lake (the Wasatch Mountains also enhance snow production due to the orographic effect).
As shown in the National Weather Service graphic below, warmer, moist air from an unfrozen lake rises into the colder air passing above and then condenses to produce bands of heavy snow on the leeward side of the lake. “Lake effect snow usually occurs during the late fall and winter months and is capable of producing as much as 2-3 inches of snow an hour with event totals ranging from 60-100 inches,” according to NASA. The process is known as bay effect snow and sea effect snow when the cold air passes over those types of water bodies.
“Megadroughts are persistent, multi-year drought events that stand out as especially extreme in terms of severity, duration, or spatial extent when compared to other droughts of the last two thousand years,” according to NOAA’s National Integrated Drought Information System. There is no consensus on the exact definition of a megadrought, but they have been recorded throughout history on all continents except Antarctica. Scientists say the American Southwest has been in a megadrought since 2000 (sometimes referred to as the “millennial drought”).
The graphic below, from a 2022 review paper, shows where and when megadroughts have occurred in the Common Era.
This paper suggested the following definition for a megadrought: “persistent, multi-year drought events that are exceptional in terms of severity, duration, or spatial extent when compared to other regional droughts during the instrumental period or the Common Era.”
Megadroughts can be caused by natural climate variability, but researchers also believe that human-caused climate change can exacerbate the problem by altering precipitation patterns and increasing evaporative demand.
The severity, duration and geographic extent of megadroughts can have profound impacts on the natural environment and human societies, with the collapse of several civilizations linked to these exceedingly dry times.
Some scientists also use the term aridificationto refer to the long-term drying of an area and argue that the process is now transpiring in the American West. “This shift in the hydrologic paradigm is most clear in the American Southwest, where declining flows in the region’s two most important rivers, the Colorado and Rio Grande, have been attributed in part to increasing temperatures caused by human activities, most notably the burning of fossil fuels,” according to a 2020 study.
Orographic lift and the rain shadow
Orographic lift occurs when an air mass ascends a mountain range or other elevated terrain. As the air rises, it cools (due to the dry adiabatic lapse rate of 5.5°F per 1,000 feet of elevation gain). If conditions are right, water vapor will condense and precipitate as the higher terrain “wrings out” the moisture. This is why the windward sides of mountains are wetter than the leeward sides, where a drier rain shadow may occur. The American West has many classic examples of the orographic effect, such as the Sierra Nevada and Cascade Mountains receiving copious precipitation as storms move in from the Pacific Ocean while areas to the east of the mountains are very dry. Even hundreds of miles inland, precipitation generally increases with altitude and the direction of the wind hitting mountain ranges plays a major role in determining snowfall amounts. Some ski areas, for example, do better with a southwest wind while others may be favored when weather comes in from the northwest. The graphics below from the National Weather Service illustrate how orographic lift around Washington’s Olympic Mountains creates a rain shadow to the east.
You may also hear the term upslope snow to describe the orographic effect, as shown in the graphic below. Along Colorado’s Front Range, an upslope storm refers to a system that pumps moisture from the plains westward toward the mountains, which receive copious snowfall due to the Rockies forcing the moisture-laden air upward.
Permafrost is a layer of soil or rock that remains permanently frozen for at least two years. Found in polar regions and high-elevation locations, permafrost is a carbon sink that releases heat-trapping greenhouse gases when it thaws. The melting of permafrost can also cause infrastructure problems and lead to rockfall in mountainous areas. “Seasonally frozen ground is near-surface soil that freezes for more than 15 days per year,” according to the National Snow and Ice Data Center. “Intermittently frozen ground is near-surface soil that freezes from one to 15 days per year.”
Polar vortex
The polar vortex is a large area of low pressure and cold air surrounding the Earth’s poles. The vortex always exists, but it gets stronger in winter and can sometimes influence the weather at lower latitudes. As shown in the graphic below, the polar vortex features a strong band of winds high in the stratosphere, around 10 to 30 miles above the Earth’s surface and far higher than the jet stream.
A strong and stable polar vortex contains cold air near the poles, but when the vortex weakens it can force cold air southward into the mid-latitudes while drawing warm air toward the North Pole.
The animation below shows what happened in January 2019, when the polar vortex caused frigid air to descend on the continental United States.
When rain falls on an existing snowpack it can lead to rapid snowmelt and flooding. A 2018 study found that rain-on-snow events are projected to become less frequent at lower elevations because of snowpack declines, especially in warmer areas like the maritime region along the Pacific Coast. At higher elevations, however, these events are expected to become more common. The greatest increase in flooding risk is projected in the Sierra Nevada, Colorado River headwaters and Canadian Rockies.
SNOTEL and snow pillows
SNOTEL (as in snow telemetry) is a network of around 900 sites that automatically measure the depth and water content of the snowpack while also providing data on temperature, precipitation and other climatic conditions. The stations use a snow pillow filled with liquid antifreeze to measure the weight of the snow above and calculate snow water equivalent (SWE), the key measure of the snow’s water content. While some stations use cellular and satellite communications, most use “meteor burst” technology to transmit their data by bouncing a radio signal off a band of ionized meteorites 50 to 80 miles above the Earth.
Using skis, snowshoes, snowmobiles or even helicopters, surveyors periodically travel to snow courses and use a metal tube known as a snow sampler to collect data at a series of points along the snow course, which is typically 1,000 feet long. By pushing the aluminum tube into the snowpack until it touches the ground, surveyors can extract a snow core that is weighed to calculate snow water equivalent (see this page from the California Department of Water Resources for lots of photos and info about how these surveys are done).
Employees of the California Department of Water Resources measure the snowpack in the Sierra Nevada on April 3, 2023. Photo: Kenneth James, California Department of Water Resources.
“Historically, snow course measurements were the first form of snowpack data collection, starting in 1906 when Dr. James Church from the University of Nevada measured a course he laid out on Mt. Rose near Reno,” according to the Natural Resources Conservation Service (NRCS). Before the advent of SNOTEL in the 1970s, snow courses were the main way the snowpack was measured, so the data for snow courses often go back much further in time.
Aerial markers are another method for measuring the snowpack in very remote locations that are tough to access. These tall metal pipes have horizontal cross members that can be seen from an aircraft, allowing surveyors to measure the snow depth. With an estimate of the snow’s density, surveyors can calculate the snow water equivalent. In recent years, NRCS has outfitted some aerial markers with sensors, as shown in the photo below.
A snow deluge is a relatively new term applied to the biggest snowpack seasons. Researchers define it as a year in which April 1 snow water equivalent is at least a 1-in-20-year event. California’s epic 2023 winter qualified as a snow deluge (and was a 1-in-54-year event, according to the scientists). Like atmospheric rivers, snow deluges can be both beneficial and hazardous. See this story for more on snow deluges and a Q&A with one of the researchers who defined the term.
Snow drought
A snow drought is a “period of abnormally little snowpack for the time of year,” according to the federal National Integrated Drought Information System, which reports that the American West “has emerged as a global snow drought ‘hotspot,’ where snow droughts became more prevalent, intensified, and lengthened in the second half of the period 1980 to 2018.”
A “dry” snow drought results from below-normal cold season precipitation, while a “warm” snow drought occurs when there is near-normal precipitation, but it falls as rain rather than snow due to warmer temperatures. Unusually early snowmelt can also cause a warm snow drought.
Snowpack, snow cover and snow line
The snowpack is the accumulation of snow on the ground, especially in mountainous areas. This natural reservoir stores water in the winter and releases it during warmer months, making it a key component of the hydrologic cycle. While the depth of the snowpack is of interest to skiers and snowboarders, water managers and researchers are particularly attuned to the snowpack’s water content, typically expressed as snow water equivalent, or how much water you’d get if you melted a column of the snowpack.
Snow cover refers to how much land is covered by snow at a specific time. While the simple presence/absence of snow does not provide information on the snowpack’s depth or water content, snow cover is still an important dimension of an area’s hydrology and geology. Compared to snow water equivalent, snow cover is easier to measure with a remote sensing technology such as satellite imagery. Snow cover acts as an insulator, protecting the ground, vegetation and animals while also increasing albedo by reflecting solar radiation. In the Northern Hemisphere, about half the land surface is covered in snow at the winter maximum.
A dataset from the National Snow and Ice Data Centerclassifies snow cover according to five classes:1) no snow, 2) ephemeral snow, 3) transitional snow, 4) seasonal snow and 5) perennial snow. The maps below show the classification for the world and the Western Hemisphere.
The snow line is the altitude that separates snow-covered from snow-free areas. The term may be applied in the short term to individual storms (e.g., a forecaster may predict at what elevation rain will turn to snow). At higher latitudes, the permanent snow line is the altitude above which snow remains on the ground year-round. In general, the higher the latitude, the lower the snow line. Rising temperatures due to climate change are leading to rising snow lines, which has major implications for the water supply, snow sports and alpine ecosystems. One study predicts that California’s snowline will be 1,600 feet higher by the end of the 21st century, causing lower-elevation ski areas to lose more than 70% of their natural snow.
Snow water equivalent (SWE)
Snow water equivalent, or SWE (pronounced as “swee”), is a critical measure of the snowpack’s water content. It reports how much water you’d get if you melted a column of snow. SWE is primarily captured by automated SNOTEL stations and manual measurements in snow courses, though it can also be calculated using aircraft and other technologies. This metric is of particular interest to water managers who need to know how much potential snowmelt lies above their reservoirs, dams, canals and distribution systems as they try to navigate between droughts and floods while meeting the needs of their customers.
Streamflow and hydrographs
The snowpack can be hard to measure, and our observations only go back so far, but scientists have a better handle on the current and historic flow of water in streams and rivers thanks to an extensive network of gauges. Streamflow is typically measured in cubic feet per second—1 cfs is equivalent to 7.48 gallons per second and will produce about 449 gallons per minute, nearly 27,000 gallons per hour, more than 646,272 gallons per day, and almost 236 million gallons per year.
A hydrograph is a data visualization that shows the streamflow rate (also referred to as discharge) at a specific point over time. Hydrographs may also show various flood stages and include both historic data and future projections. The image below shows an example of the hydrographs produced by NOAA. See this page from the National Weather Service for definitions of terms related to hydrographs.
National Avalanche Center Encyclopedia. The National Avalanche Center provides an excellent glossary and encyclopedia on avalanche terminology. Created by Doug Abromeit, Bruce Tremper and many other avalanche professionals, this resource provides definitions of 74 terms along with many helpful graphics, photos and diagrams.
Snowpack Monitoring in the Rocky Mountain West: A User Guide. This 2020 report from the Western Water Assessment at the University of Colorado Boulder is an excellent guide to the region’s snowpack, how it’s monitored and how you can access data from a variety of sources.
Colorado River Basin Climate and Hydrology: State of the Science. This 2020 report is another helpful publication from the Western Water Assessment. It discusses the basin’s weather, climate and hydrology, plus how climate change is affecting the river’s flow.
SnowSlang is a personal passion project of mine that includes a master glossary and individual posts on key terms related to snow, skiing, snowboarding and the alpine environment.
The Water Desk is excited to announce the participants for the Rio Grande Journalist Training and Workshop, taking place in Albuquerque, New Mexico, in January 2025.
This training program will bring together journalists dedicated to enhancing coverage of water issues along the Rio Grande, fostering collaboration among news outlets and deepening understanding of critical challenges facing the region.
The Rio Grande flows from the Rocky Mountains of Colorado, through New Mexico and Texas, while forming the U.S.-Mexico border. Like many Southwestern waterways, the river has been ravaged by a more than two-decade-long dry spell made worse by climate change. Coverage of the communities and ecosystems dependent on the Rio Grande is essential to understanding what’s at stake as the gap between water supply and demand widens.
The Water Desk selected 14 journalists to participate in the training, reflecting diversity in geography, race, ethnicity, gender and medium.
Participants:
Spenser Heaps, Indepdendent
Catherine Jaffee,Independent
Elizabeth Miller,Independent
Jeremy Miller,Independent, contributing writer, Sierra Magazine
Caitlin Ochs,Independent
Danielle Prokop,Source NM
Martha Pskowski, Inside Climate News
María Ramos Pacheco, The Dallas Morning News
Elliot Ross, Independent
Nadav Soroker, Searchlight New Mexico
Ishan Thakore, Colorado Public Radio
Caroline Tracey, Independent
Emery Veilleux, The Taos News
Christian von Preysing, KRGV-TV
As part of The Water Desk’s training program, participants will hear from legal experts, water users and tribal members along the Rio Grande to hear varying perspectives on how the river is a key part of the region’s cultural, political and geographic landscape.
The workshop will feature expert-led sessions on the complexities of water management and opportunities to network with peers and regional water experts. The Thornburg Foundation, a Santa Fe-based family foundation, is providing the financial support to make this training possible, while the program is the sole responsibility of The Water Desk.
The site where Ute Water plans to build Owens Creek Reservoir at 8,200 feet on the Grand Mesa was snow covered by mid-November. The Western Slope’s largest domestic water supplier has conditional water rights for the 7,000-acre-foot reservoir. Photo: William Woody
Just add waterThe site where Ute Water plans to build Owens Creek Reservoir at 8,200 feet on the Grand Mesa was snow covered by mid-November. The Western Slope’s largest domestic water supplier has conditional water rights for the 7,000-acre-foot reservoir. William Woody
Nearly two hours east of Grand Junction on a remote dirt road on the Grand Mesa is a nondescript, shallow, sage-brush-covered valley where two creeks meet.
The site, at 8,200 feet in elevation, is home to a wooden corral where ranchers with grazing permits gather their livestock and to the Owens Creek Trailhead where hikers set out for nearby Porter Mountain.
It’s also the spot where the largest domestic water provider on Colorado’s Western Slope plans to someday build a reservoir. The proposed Owens Creek Reservoir is modest in size, at about 7,000 acre-feet. It would help Ute Water Conservancy District satisfy the needs of its 90,000 customers into the future.
“Our job as a water provider is never done,” said Greg Williams, assistant manager at Ute Water. “You can develop one and you move onto your next project and go through that same process.”
Ute Water Assistant Manager Greg Williams, left, stands at the site of the proposed Owens Creek Reservoir on the Grand Mesa. Cities across the state have conditional water rights that save their place in line while they work to develop projects. William Woody
In most cases, water in Colorado must be put to beneficial use to keep a right to use it on the books. The cornerstone of Colorado water law is the system of prior appropriation, where the oldest water rights get first use of rivers. And hoarding water rights without using them amounts to speculation, which is illegal. But a Colorado water law feature known as a conditional water right allows water-rights holders to skirt this requirement and hold their place in line. The conditional water rights for the proposed Owens Reservoir date to 1972, although work to build this particular reservoir appears limited to preliminary studies and work on other related components of Ute Water’s system.
Ute Water, along with many other cities, conservancy districts and oil and gas companies across the Western Slope, are hanging on to water rights that are in some cases a half-century old without using them. Conditional water rights allow a would-be water user to reserve their priority date based on when they applied for the right, while they work toward eventually using the water. The result is millions of acre-feet worth of conditional water rights on paper that have been languishing for decades without being developed. Some of these rights are tied to large reservoir projects.
An analysis by Aspen Journalism found that across Colorado’s Western Slope, cities, conservancy districts, fossil fuel companies and private entities hold conditional water rights that would store about 2.6 million additional acre-feet from the Colorado River and its tributaries in not-yet-built reservoirs each bigger than 5,000 acre-feet. This is a staggering amount of water storage and more than the entire state of Colorado currently uses from the Colorado River basin, which is about 2.1 million acre-feet a year.
Most of this water would be stored in not-yet-built reservoirs, each bigger than 5,000 acre-feet. In some cases, the water would be stored in already-existing reservoirs, using conditional rights that would allow the reservoir to be refilled or enlarged.
Ute Water has plenty of company among the state’s conditional water rights holders. The Glenwood Springs-based Colorado River Water Conservancy District has rights from 1972 for the 66,000-acre-foot Wolcott Reservoir on Ute Creek in Eagle County; Mountain Coal Company says it wants to build the 75,000-acre-foot Snowshoe Reservoir on Anthracite Creek near Kebler Pass with rights from 1969; and Denver Water has plans for the 350,000-acre-foot Eagle-Colorado Reservoir on Alkali Creek in Eagle County using water rights from 2007. These are just a few examples of the 94 conditional water rights for new and existing reservoirs of 5,000 acre-feet or more planned for western Colorado identified by Aspen Journalism.
The 1922 Colorado River Compact promised 7.5 million acre-feet to the Upper Basin, which so far has never come close to using its half. The state of Colorado has the right to use 51.75% of the Upper Basin’s allocation.
In a way, this planned water development represents the hopes and dreams for the future growth of the Colorado River’s Upper Basin states — Colorado, Wyoming, Utah and New Mexico. The 1922 Colorado River Compact promised 7.5 million acre-feet to the Upper Basin, which so far has never come close to using its half. The state of Colorado has the right to use 51.75% of the Upper Basin’s allocation.
But some experts say these proposed reservoirs are unrealistic wishes of the past, a vestige of the mid-20thcentury frenzy of dam building across the West that is mismatched for 21st century conditions. They say if this scale of future development comes to pass, it would upend the system of water rights, as well as harm the environment. They say the water court system that keeps these phantom reservoirs alive is being abused and should be reformed. In the era of historic drought, climate change and crashing reservoir levels, where users already see shortages in dry years, some say this amount of water for new development simply does not exist.
The Colorado River flows past a golf course near Parachute. Cities, conservancy districts, energy companies and private entities have conditional water rights for 2.6 million acre-feet of water to be stored across the Western Slope. William Woody
The Upper Basin’s dreams of water development also highlight a central tension at the heart of the current disagreement between the Upper Basin and the Lower Basin states of California, Arizona and Nevada. The two sides have not been able to reach an agreement about how the river’s two largest storage buckets, Lake Powell and Lake Mead, should be operated in the future and how cuts should be shared in drought years. Negotiations are currently at an impasse.
“If all these water rights were developed, it would be a disaster. I think everybody understands that.”
Mark Squillace, a natural resources law professor at the University of Colorado Boulder
Over the past 100 years, the Lower Basin has fully developed its share of the river and then some. The Upper Basin has not, but it believes it is still entitled to, despite the contradictory nature of both committing to conservation while holding on to plans for new future uses.
“It’s especially a problem when we’re trying to find more water to reduce the amount of depletion on the Colorado River,” said Mark Squillace, a natural resources law professor at the University of Colorado Boulder. “If all these water rights were developed, it would be a disaster. I think everybody understands that.”
Holding on to conditional rights
The Colorado River meanders through the Grand Valley, where it turns peach orchards and alfalfa fields green. Ute Water, the largest domestic water provider on the Western Slope, plans to build additional reservoirs to serve its Grand Valley customers. William Woody
Entities can’t just hang on to conditional water rights in perpetuity. To maintain a conditional right, an applicant must every six years file what’s known as a diligence application with the state’s water court, proving that they still have a need for the water, that they have taken substantial steps toward putting the water to use and that they “can and will” eventually use the water. They must essentially prove they are not speculating and hoarding water rights they won’t soon use.
A cottage industry has sprung up around these diligence filings. Engineering firms produce studies that show a conditional water rights holder has worked to develop the water right. Attorneys file diligence applications with the water court and then see them through the sometimes yearslong process to get it renewed for another six years.
Aspen Journalism’s analysis looked at only the biggest proposed reservoirs on the Western Slope, but every year, hundreds of diligence applications are filed statewide for smaller amounts of water.
And the bar for proving diligence is low.
“It’s only limited by the imagination of the lawyer who’s filing the application about what you can claim for diligence,” said Aaron Clay, a longtime water attorney and water court referee in the Gunnison River basin, who teaches community courses about the basics of water law across the Western Slope.
The standard for reasonable diligence is much lower now than it was decades ago, Clay said, because state officials want at least some of these reservoirs to be built. The thinking is practical and political: Building more reservoirs makes it easier to control the timing and amount of water Colorado lets flow downstream.
Water court judges are hesitant to abandon these conditional water rights, even if they have been languishing without being used for decades partly because in Colorado water is treated as a fully vested property right, where the state may have to compensate water rights holders if they take it away from them. And owners of these rights believe they are valuable and are reluctant to let them go. The status quo is maintained because there’s no incentive for anyone to scrub these unused water rights from the books.
Water court judges are hesitant to abandon these conditional water rights, even if they have been languishing without being used for decades.
Some entities, such as Ute Water, have conditional water rights for several reservoirs, pipelines, pumping stations and other components of an integrated system. Applicants are not usually required to file separate diligence applications for each of the system’s components. For example, in Ute Water’s most recent diligence filing for Owens Reservoir, the conservancy district filed a combined application for 14 different components of an integrated system. The application, filed in August and still pending in Division 5 of water court, claims that work on one feature of the system constitutes reasonable diligence on all the features of the system.
Municipal water providers such as Ute Water are given special deference under Colorado water law through something called the Great and Growing Cities Doctrine.
“The standard for diligence for a municipality is even lower,” Clay said. “We’re going to give them a little leniency with diligence by saying if you can still show us you’re going to need that water 30, 40, 50 years from now and you’re doing something toward it — studying it, working on the environmental issues or whatever — that’s going to be enough diligence to get you by for another six years.”
Owens Reservoir is just one of several Ute Water plans to develop. Williams said they are currently working to enlarge Monument Reservoir No. 1 and will then explore building Buzzard Creek Reservoir, Willow Creek Reservoir and Big Park Reservoir, all on the Grand Mesa.
“It remains to be seen the timing of when those reservoirs would be developed,” Williams said. “But our intent would be to continue developing each one of those sources.”
Squillace said that although he understands cities may need more leeway when it comes to long-term water planning, there is a lot of abuse of the conditional water rights system. The state water courts should be tougher on denying claims of diligence and stop granting extensions to water rights that haven’t been developed despite having had decades to do so, he said.
“You’re not supposed to sit on them for 20, 30, 40 years before you develop them,” he said. “It’s the failure of the state water courts to take diligence requirements seriously. They just apparently seem to give out these extensions of water rights without a whole lot of showing that there’s actually any kind of diligent work toward developing the water. I think it’s a huge problem.”
Uncertainty hangs over decades-old proposed reservoirs
Smaller proposed reservoir sites are scattered across Grand Mesa in western Colorado, and are underpinned by decades-old conditional water rights. William Woody
One way in which these conditional water rights could present a problem is the uncertainty they create for the state’s other water users, especially those who have put their water to use in the past 60 or so years.
Andrew Teegarden is a fellow at the Getches-Wilkinson Center for Natural Resources, Energy and the Environment at the University of Colorado School of Law. The University of Denver Water Law Review plans next fall to publish his paper “Uncertain Future: How Conditional Water Rights Have Created Unintended Consequences in Colorado.” When the owners of conditional water rights with older priority dates finally begin diverting water that they have not used for decades, they may cut off junior water users who began using water between the conditional right’s older date and the present day. Teegarden calls this “line-jumping,” and if all these proposed reservoirs were developed, it could upend the entire priority system.
If all these proposed reservoirs were developed, it could upend the entire priority system.
The solution, he said, is for Colorado to stop treating conditional rights as property rights. Lawmakers could also reform diligence standards and impose a strict time limit, such as 50 years, for applicants to put their water to beneficial use. Otherwise, these conditional rights should be abandoned.
“Clearly, the history and precedent surrounding conditional rights were well-intentioned on giving users within the system flexibility to implement large-scale projects and the security to hold their place in priority,” the paper reads. “These rights, though, come with unintended consequences and it is vital that reforms be implemented before people begin seeing their water rights curtailed or diminished.”
If these proposed dams are built, they could also have a negative impact on the environment. Western Resource Advocates and several other nonprofit and government organizations within Colorado work to improve riparian habitats and keep water flowing in rivers for the benefit of fish and ecosystems. Many of the groups’ projects try to mitigate the effects of cities and agriculture taking too much water out of rivers.
If these proposed dams are built, they could also have a negative impact on the environment.
John Cyran, senior attorney with WRA’s Healthy Rivers Program, said this 2.6 million acre-feet of proposed reservoirs is a time bomb.
“Given that so many streams are already in stressed positions, it’s a big problem for the environment,” Cyran said. “We’re trying to look at the river as it is now and figure out how we can make it healthier. If a bunch of new claims come on the river, that work will be for nothing.”
Cyran brings up another potential issue with conditional water rights: They are able to be bought, sold, changed and transferred to another owner, another location or another type of use. In October, the Middle Park Water Conservancy District transferred conditional rights for a 20,000 acre-foot reservoir on Troublesome Creek near Kremmling to a private ranch for just $10. Some worry that this Western Slope water could be sold to the Front Range. And WRA is opposing another instance in the White River basin where an oil and gas company wants to transfer its storage rights to a new location.
“We’re trying to look at the river as it is now and figure out how we can make it healthier. If a bunch of new claims come on the river, that work will be for nothing.”
John Cyran, senior attorney with WRA’s Healthy Rivers Program
“The idea is supposed to be a conditional right saves your place in line,” Cyran said. “There should be restrictions on water users trying to change those rights to some new purpose while retaining their senior priority. If you can’t use it for what you intended, it goes back to the river. You don’t get to use it for something else, and you don’t get to sell it to somebody to use for something else.”
Future water development tensions persist on Colorado River
But perhaps the biggest issue with 2.6 million acre-feet worth of new water storage may be the effect on, and implications for, the Colorado River basin as a whole. Water managers from each of the seven basin states are in the midst of hammering out a deal that would decide how Lake Powell and Lake Mead are operated and how cuts are shared among the seven states beyond 2026.
The Colorado River flows along I-70 in De Beque Canyon just east of the Grand Valley. Water users hold rights to store an additional 2.6 million acre-feet from the Colorado River and its tributaries in proposed reservoirs on the Western Slope. William Woody
Colorado officials have been rolling out new talking points, which include that the Upper Basin already uses about 30% less water in dry years because the water simply isn’t there, so the Lower Basin should take a corresponding proportionate cut of 30%.
At a time when water managers are debating how to share cuts in a hotter, drier future and where some water users are already suffering shortages, why is this large scope of water development in western Colorado still planned?
JB Hamby, chair of the Colorado River Board of California and the state’s lead negotiator in Colorado River talks, who also serves on the board of the Imperial Irrigation District, which is the biggest water user on the Colorado River, laughed when Aspen Journalism told him that Colorado has plans to develop 2.6 million acre-feet worth of new reservoirs on the Western Slope.
“That’s crazy,” he said.
At a time when water managers are debating how to share cuts in a hotter, drier future, why is this large scope of water development in western Colorado still planned?
Hamby said building 20th century-style infrastructure to develop more water in the Upper Basin does not make sense. He said all water users in the basin should be working together to find ways to collectively reduce their use. That includes navigating differing interpretations of the Colorado River Compact without involving the U.S. Supreme Court.
“That’s our best step forward, not pretending like it’s 1965, which it is not,” Hamby said.
Hamby was getting at something that is a major sticking point between the Upper and Lower basins: two different interpretations of an aspect of the 1922 Colorado River Compact.
The agreement assumed there was 16 million acre-feet of available water each year, with 7.5 million acre-feet each allocated to the Upper and Lower basins. The goal was to reserve an equal portion of the river’s flows for the Upper Basin to prevent rapidly growing California from taking all the water. Giving half to the Upper Basin ensured that the states could slowly grow into their full allocation.
A century later, the Upper Basin still has not done that and currently uses about 4.3 million acre-feet a year. Experts have pointed out that 16 million acre-feet was an overestimate of how much water was available to begin with, and after two decades of being wracked by drought and climate change, that amount of water surely no longer exists in the Colorado River basin system. The foundation of the Colorado River Compact was flawed.
Upper Basin water managers cling not only to what was promised to them 100 years ago but to the belief that as long as they don’t use more than the 7.5 million acre-feet allocated to them, they will not be in violation of the compact. However, some Lower Basin advocates believe that regardless of the Upper Basin’s use, the upstream states could be subject to a compact call if they don’t deliver 7.5 million acre-feet a year. Because river flows have diminished over the past 20-plus years, additional use in the Upper Basin could exacerbate shortages and trigger litigation from the Lower Basin in the form of a compact call, which could force cuts on the Upper Basin. Legal uncertainties about how a compact call could unfold complicates the dynamic and heightens animosity between the two basins.
Amy Ostdiek, chief of the interstate, federal and water information section of the Colorado Water Conservation Board, said an additional 2.6 million acre-feet of reservoir storage won’t increase the risk of a compact call.
“We have the right to the beneficial use of 7.5 million acre-feet a year and in the Upper Basin, Colorado gets 51.75% of the available supply,” she said. “I do not see these projects as putting us in danger of going over that number.”
Upper Basin water managers cling not only to what was promised to them 100 years ago but to the belief that as long as they don’t use more than the 7.5 million acre-feet allocated to them, they will not be in violation of the compact.
According to Jason Ullmann, Colorado’s head engineer at the Department of Water Resources, 2.6 million additional acre-feet of water exists in some years and could be developed, especially since most of that would be captured as spring runoff. The way reservoirs typically work is by storing snowmelt in the spring and releasing it as needed later in the year. But any new reservoir would be at the mercy of the particular and variable hydrologic conditions of any given year and may not always fill.
“Typically, storage buckets, the larger ones in particular, they may not accomplish a full fill every year,” Ullmann said. “It may not be a [2.6 million acre-foot] draw on the river every year. It’s just a water right for that amount of storage.”
Hamby said the Upper Basin point of view is one of the past and out of alignment with the hydrology of the river, which has been declining over the past two decades and is expected to continue to decline.
“The idea of developing new infrastructure to put more water to use does not make sense in this century,” he said. “And while there may be feelings of promises from 1922, this is 2024.”
What if it was all a dream?
One reason these proposed reservoirs don’t seem to worry many water managers is because nobody believes they will ever all be built. Although these projects represent the desires of the Upper Basin, this scale of development may be just a pipe dream.
Eric Kuhn, a Colorado River expert, author and former general manager of the Colorado River District, doubts that many of these reservoirs will be built, but not because the water isn’t there or because of the permitting hurdles, environmental impacts or expense of construction. Rather, Kuhn says there’s no longer a need for many of these storage buckets.
Some of these conditional rights, especially in the Yampa-White-Green River basin, are associated with oil shale development, which has become less economically feasible in recent years. There are no new large-scale federally subsidized irrigation projects on the horizon. And as more agricultural land is converted to residential developments across the West, water use goes down.
Oil and gas wells line the Colorado River along a rural stretch of western Colorado. Energy companies hold conditional water rights across the region, many linked to the potential future development of oil shale. William Woody
Cities such as Aurora and Las Vegas have implemented aggressive conservation programs and have proved they can grow without using a lot more water. As the Upper Basin continues to urbanize, it may never grow into its 7.5 million-acre-foot allocation. The only reservoirs that will realistically be built, Kuhn said, will be small (1,000 acre-feet or less) and on a creek where there’s municipal demand.
“Maybe you need additional storage for streams that don’t have enough storage today, but that’s a tiny, minute amount,” he said. “Conditional water rights are a product of 50, 60, 70, 80 years ago, when they had a purpose. I don’t even see that they have a purpose anymore. They also represent a whole bunch of projects that, if they had been economically feasible, would have been built a long time ago.”
“Conditional water rights are a product of 50, 60, 70, 80 years ago, when they had a purpose. I don’t even see that they have a purpose anymore.”
Eric Kuhn, former general manager of the Colorado River District
Although many entities continue to hang on to conditional water rights that they are unlikely to develop, some are starting to take a more clear-eyed approach, recognizing that some of these phantom reservoirs are dreams of the past and letting them go.
The River District has abandoned conditional reservoir rights on the Crystal River and other places; in January, a company with ties to oil shale development abandoned rights for a reservoir on Thompson Creek south of Carbondale; Colorado Springs recently gave up water rights for reservoirs in Summit County; and in October, the town of Breckenridge let go of water rights for two reservoirs on the Swan River but kept rights for a third: Swan River Reservoir No. 4.
James Phelps, director of public works for the town of Breckenridge, said they didn’t file the diligence claims this time for Swan River Reservoirs Nos. 1 and 2, which had water rights dating to 1981, because the town doesn’t need to develop that much reservoir capacity. Other factors in the town’s decision to not keep the reservoirs alive were the huge financial costs; the fact that housing developments encroached on the reservoir sites; and disturbance to the ecosystem in a place where residents place a high value on the environment.
“It was determined that if there was a need for the water in the future, whatever that need may be, we wouldn’t need to develop all three of those,” Phelps said. “We know that developing reservoirs is not an easy thing to do.”
Despite Colorado water courts’ tendency to rubber-stamp most diligence applications to keep alive decades-old unused water rights, there is at least one recent example of legal pushback on a reservoir enlargement project.
In October, a federal judge ruled that Denver Water’s Gross Reservoir expansion violated the Clean Water Act because it didn’t take into consideration the potential for a Colorado River Compact call and the declining hydrology of the basin. Although it’s unclear if this ruling would set a precedent for any other dam and reservoir project in Colorado, it signals a growing understanding of the risks that new water development could pose to the entire Colorado River system.
“The Colorado River Compact rests on a politically unpalatable truth — the Compact promised the basin states water that simply does not exist,” a footnote in the ruling reads. “The Court emphasizes this context for good reason: The cracked foundation of the Colorado River’s management system all but demands skepticism over any proposal that will affect the hydrology of the Colorado River basin.”
This story was produced by Aspen Journalism, in partnership with The Water Desk at the University of Colorado Center for Environmental Journalism.
How we produced this report
Aspen Journalism used publicly available data on conditional water rights from the Colorado Division of Water Resources to produce the interactive map of Western Slope reservoirs over 5,000 acre-feet. Information from this state database was confirmed for accuracy with state officials, who verified it was current as of September 2024. Information about who owns each water right was found in water court filings. We have mapped the reservoirs to the best of our knowledge by cross-checking publicly available information with water court filings, but inaccuracies may still exist.
This project looks at only the water rights for the largest 94 conditional reservoir water rights over 5,000 acre-feet on the Western Slope. Most of these would be stored in not-yet-built reservoirs. Some of this water would be stored in existing reservoirs using conditional rights that would allow the reservoir to be refilled or enlarged. There are more water rights for storage amounts smaller than 5,000 acre-feet, which Aspen Journalism did not attempt to quantify, meaning there is more than 2.6 million acre-feet of new reservoir storage planned for western Colorado.
Groundwater pours from an irrigation well in Buckeye, Arizona, an area of the state that has brackish groundwater both near the surface and deep underground. (J.Carl Ganter/ Circle of Blue)
The numbers are so vast, so enticing that they tantalize like a desert oasis.
Deep below the surface in Arizona – roughly a quarter mile underground – sit large volumes of water that are less salty than the ocean, but not easily used. At a depth of 1,200 to 1,500 feet, between 530 million and 700 million acre-feet fill this layer statewide.
If it were all pumped to the surface and purified, this brackish groundwater would supply Arizona’s water needs for a century or more. Problem is, it can’t all be pumped.
Though the numbers are legitimate – and detailed in an updated state assessment that was published in August – the reality for brackish groundwater, at this point, is more of a mirage. Exploiting this resource to satisfy the state’s demand for water in an arid climate is not as simple as drilling wells.
“This is not a new supply of water,” said Juliet McKenna, a hydrogeologist with Montgomery & Associates, the consulting firm that the state contracted for the brackish groundwater assessment. “This is physically groundwater and this is legally groundwater. And there are consequences and restrictions in both areas for trying to use this.”
McKenna, who managed the assessment, and other state water experts interviewed for this story explained that brackish groundwater has a slew of impediments – environmental, physical, financial, technical, regulatory, and legal – that limit its use, despite the efforts of enthusiastic backers in the Arizona Legislature who are looking for ways to counter the state’s declining Colorado River supplies.
“Brackish groundwater is still groundwater, right?” echoed Patrick Adams, water policy adviser to Gov. Katie Hobbs. “So its extraction impacts the aquifer as much as any other groundwater supply when it’s removed from storage. And really that needs to be considered – and its use needs to be considered –against that backdrop. Where’s the brackish groundwater located? What are the local groundwater conditions? What’s the health of the aquifer?”
Securing a reliable water supply is an existential question for high-growth Arizona and its desert economy. The Colorado River, a major source for central Arizona, has sputtered in the last two decades amid hotter, drier weather attributed to a warming climate. The state’s allocation from the river was whittled by at least 18% in each of the last three years. New operating rules that are under negotiation will likely extend or deepen those cuts past 2026, when current guidelines expire.
Water, as a result, is prominent in state policy debates.
Drilling into Arizona’s Brackish Supplies
A desire for more data on its water sources is why the Legislature inserted $50,000 for an updated brackish groundwater inventory in the 2023 budget. The Arizona Department of Water Resources then commissioned Montgomery & Associates to do the analysis.
Arizona is not alone in its quest to better understand its subsurface water. New Mexico is looking to expand its water supply by treating both brackish groundwater and the high-salinity, chemical-laden water that gushes out of oil and gas wells. To the east, the Texas Water Development Board has investigated and mapped the state’s brackish groundwater zones for the last 15 years. A $1 billion water fund approved by voters last year will include at least $250 million for marine and brackish water desalination.
The Arizona inventory identified 21 areas with brackish groundwater, four of which the state singled out for more detailed assessment. One focus area is the Little Colorado River Plateau, in the state’s northeast corner. About half of the assessed brackish groundwater is located there. (The assessment defined brackish groundwater as having total dissolved solids greater than 1,000 parts per million. Sea water, by comparison, is 35,000 parts per million.)
The other areas – Gila Bend, Ranegras Plain, and West Salt River Valley – are closer to the population centers in Maricopa County or to the Central Arizona Project canal that moves water across the state.
“We wanted it to be meaningful or useful,” said Ryan Mitchell, chief hydrologist for the state’s Department of Water Resources, about selecting the focus areas.
A kiosk in Bouse, Arizona, advertises “salt free” drinking water. The town is located in Ranegras Plain, one of the areas assessed in the state’s brackish groundwater inventory. (Brett Walton / Circle of Blue)
The discussions around brackish groundwater are as much about its limitations as its possibilities. McKenna pointed out several challenges. One, water in storage does not equal available water. The same physical drawbacks from pumping fresh groundwater also apply to brackish. As groundwater is pumped, the land above can crack and sink, damaging houses, roads, and other public infrastructure. The water table can drop and cause neighboring wells to go dry. Those outcomes can occur with relatively modest levels of pumping, let alone with a massive drawdown to access all the deep brackish groundwater assessed in the inventory. In an arid region, water at that depth is essentially non-renewable.
“If we dewatered those aquifers to 1,500 feet below ground surface, that’s an apocalyptic scenario,” McKenna said. “So we’re not pumping groundwater to those depths under any reasonable scenario. So the estimate of water that is there, in aggregate, does not translate to water that’s available for folks to use.”
Water is already used unsustainably in the study’s four focus areas. Each is currently operating at a groundwater deficit, McKenna said. More water is pumped out than is recharged.
Steep Challenges Remain in Using Brackish Water
Even if brackish groundwater is physically available, it is not necessarily desirable. Buckeye, one of the state’s fastest growing cities, sits within the Buckeye Waterlogged Area, located on the western outskirts of the Phoenix metro area. “Waterlogged” is a regulatory definition based on the area’s unique hydrogeology at the junction of three rivers: the Agua Fria, Gila, and Salt. Water pools here, and farmers have to pump it out so that their crops will grow. Due to salts in irrigation return flows, the water is brackish in places near the surface.
Buckeye, which pumps groundwater for its municipal supply, is surrounded by brackish groundwater, but Terry Lowe, the water resources director, says the city avoids it. For Buckeye, brackish groundwater is “not deployable,” as he puts it. Some of the Buckeye Waterlogged Area groundwater is between 3,000 and 4,000 parts per million of total dissolved solids, and the equipment and energy required to remove the salts is not cheap. “Treating that out is a waste of money,” he said.
What’s more, brackish groundwater has complications that involve waste disposal. Treating brackish groundwater produces a concentrated brine that must be handled delicately and expensively. Small quantities might be handled by a wastewater treatment plant. Large volumes are typically injected deep underground, but in Arizona that method is “effectively prohibited” without policy changes, a governor’s water council determined in 2022. The Arizona Department of Environmental Quality, the permitting agency for aquifer protection, said that no Class I deep injection wells operate in the state. Carollo, an engineering firm, concluded that cheaper brine disposal was essential for brackish groundwater to become an “economically viable water supply” in the state. Lowe also cited brine management as a reason his department shies away from brackish groundwater.
Then there are the legal and regulatory hurdles. The Legislature passed the Groundwater Management Act in 1980 in response to unsustainable use. It established Active Management Areas (AMA) to steward a finite resource. In practice, most users in the six AMAs need permission to pump and must replace a portion of their use. In the Phoenix AMA, which roughly corresponds with Maricopa County but also extends into neighboring Pinal, the goal is “safe yield” by 2025 – balancing groundwater extraction with recharge. It is not on track to meet that deadline. Incentivizing brackish groundwater use could put safe yield farther out of reach.
Farmers in the Buckeye Waterlogged Area must contend with elevated groundwater salinity. The area’s unique hydrogeology and irrigation legacy has resulted in salty groundwater near the surface. (Brett Walton / Circle of Blue)
And one more headwind: Arizona restricts the movement of groundwater within the state. Five groundwater basins are designated as “transport” basins. Water in these areas can be pumped and exported to an AMA. Most other groundwater must be used in its basin of origin. Without a change in legal status, brackish groundwater would be stranded in place, able to be used locally but not moved to the areas of highest demand.
“For us it’s still considered groundwater,” Mitchell said. “It’s still regulated the same, it’s still accounted for and tracked and all the authorities are still in place, whether it’s brackish or fresh, it’s still treated the same.”
The Search for Water
To state Rep. Alexander Kolodin, these hurdles – physical, financial, regulatory – are obstacles that can be overcome. Kolodin, a Republican who represents northeastern Maricopa County, is the most enthusiastic booster of brackish groundwater in the Legislature. He sees the big number in the updated inventory and grows excited.
“Arizona is sitting on an absolute ocean of brackish groundwater,” he said. With the state’s take from the Colorado River declining, Kolodin wants to consider other sources of water that could fill the gap. “I’m very interested in figuring out how we can tweak the law to utilize this resource’s maximum potential.”
Those tweaks at the state level, he said, would include reducing groundwater replenishment requirements in the AMAs for brackish water and relaxing the restrictions on moving groundwater out of its natural basin. “If you can’t transport it, you never really have much incentive to do it in rural areas because it’s still much more costly than our historical sources of water,” he said.
Kolodin advocated for $11 million in the state budget last year for a brackish groundwater pilot program. The Department of Water Resources published a request for information in October 2023. The pilot didn’t go much farther than that. Mitchell, who reviewed the submissions, said they read more like “qualifications packages” than a careful project plan. Due to a state budget shortfall this year, funding for the pilot was retracted.
Brackish groundwater boosters like Kolodin note the efforts in Texas, where the state government mapped its brackish reserves, estimated yields, required impacts analysis, and provided financing. El Paso has the country’s largest inland desalination facility, which has a production capacity of 27.5 million gallons a day. Mitchell, however, points out that the comparison is not one-to-one. Arizona has different hydrogeology, as well as more stringent legal and regulatory requirements.
The hunt for new water supplies is a longstanding feature of Arizona politics, extending back to the pursuit of the Central Arizona Project canal in the mid-20th century. In recent years, the prospectors have sought to turn salty water fresh.
A decade ago, under Gov. Jan Brewer, the state produced the Arizona’s Next Century report, which listed brackish groundwater as one of seven potential sources to augment the state’s supply.
Water augmentation was a major focus of Gov. Doug Ducey’s administration. In 2015, Ducey signed an executive order to establish the Governor’s Water Augmentation Council. In 2019, he signed another executive order that expanded the work to “investigate long-term water augmentation strategies for the state.” The Governor’s Water Augmentation, Innovation, and Conservation Council lasted until Gov. Hobbs was elected. In 2023, Hobbs formed the Governor’s Water Policy Council.
The Hobbs administration is less focused on brackish groundwater than her predecessors. The Governor’s Water Policy Council report, published earlier this year, does not mention it by name.
“Brackish groundwater development as a source for augmentation is not really at the forefront of where the Water Policy Council is focusing its efforts,” Adams, the governor’s water policy adviser, said.
For now, as more data is collected, brackish groundwater will remain just off center stage, with lingering questions about how and when it should be used.
“If it were to be utilized, it needs to be done so thoughtfully and mitigate impacts from pumping,” McKenna said. “It’ll be expensive, in terms of treating and permitting. But it is a supply that’s in our state, and like our other water supplies, I think we need to think about it and make thoughtful decisions about how to use it, if we want to use it.”
This story was produced by Circle of Blue, in partnership with The Water Desk at the University of Colorado Boulder’s Center for Environmental Journalism.
Employees of the California Department of Water Resources measure the snowpack in the Sierra Nevada on April 3, 2023. Photo: Kenneth James, California Department of Water Resources.
If you’re looking to gauge the depth and extent of the West’s snowpack, there are tons of helpful resources online that offer data, maps and graphics on both current and historical conditions.
This page offers a tip sheet to help navigate a variety of sites and briefly explains some of the technologies used to generate the data behind the visuals.
I’ve focused on websites that make it relatively easy for the general public to explore the data, especially with interactive maps, rather than pointing to more technical tools geared toward scientists and water managers.
The most popular source for data on the West’s snowpack is the federal Natural Resources Conservation Service (NRCS), which provides a wealth of information from automated SNOTEL sensors and manually measured snow courses.
SNOTEL (as in SNOw TELemetry) is a network of around 900 sites that automatically measure the depth and water content of the snowpack while also providing data on temperature, precipitation and other climatic conditions. The stations use a “snow pillow” filled with liquid antifreeze to measure the weight of the snow above and calculate snow water equivalent (SWE), the key measure of the snow’s water content.
While some stations use cellular and satellite communications, most use “meteor burst” technology to transmit their data by bouncing a radio signal off a band of ionized meteorites located 50 to 80 miles above the Earth.
The photo below from NRCS shows what a typical SNOTEL station looks like.
SNOTEL remains the backbone of snowpack monitoring in the West, but it does have limitations. The sites are typically located in high-elevation clearings where snow persists, so this sample of locations doesn’t capture the full gamut of conditions across the vast landscapes where snow accumulates. The SNOTEL station only collects data for a single point, but conditions may vary dramatically just a short distance away due to trees, wind, shade and other factors.
In addition to using SNOTEL stations, the NRCS collects data manually in snow courses. Using skis, snowmobiles or even helicopters, surveyors periodically travel to the sites and use a metal tube known as a snow sampler to collect data at a series of points along the snow course, which is typically 1,000 feet long. By pushing the aluminum tube into the snowpack until it touches the ground, surveyors can extract a snow core that is weighed to calculate the SWE (see this page from the California Department of Water Resources for lots of photos and info about how these surveys are done).
Aerial markers are also used to measure the snowpack in remote locations that are tough to access. These tall metal pipes have horizontal cross members that can be seen from an aircraft, allowing surveyors to measure the snow depth. With an estimate of the snow’s density, surveyors can calculate the SWE. In recent years, NRCS has outfitted some aerial markers with sensors, as shown in the photo below.
Several sites discussed below also use satellite data to monitor the snowpack, particularly images from the Moderate Resolution Imaging Spectroradiometer (MODIS). Although current satellite technology is unable to gauge SWE, the MODIS data does show whether snow is covering the ground while also providing information on melting, the size of snow grains and other variables.
See this page from NRCS for more information on snowpack monitoring. This page provides an overview of the NRCS snow surveys and its water supply forecasting.
Visualizing NRCS snowpack data
The best place to start is the National Water and Climate Center iMap, which allows you to create maps showing conditions at individual sites and basins (see this page for help on using the tool and this page for generating detailed reports).
The image below shows just one of the many views you can generate with the iMap tool. In this case, the map is displaying conditions for April 1, 2024, with the West’s many river basins shaded according to the percent of the median for 1991-2020. The circles show individual SNOTEL stations.
In addition to visualizing SWE, the iMap tool includes a ton of other data, including snow depth/density, soil moisture/temperature, streamflows and reservoir storage.
This page from NRCS offers some pre-defined maps and reports on the West’s snowpack.
NRCS state-level data
Another way to track the snowpack is by visualizing NRCS data for individual states. This page includes links to maps for 12 Western states and an overview of the region, as shown in the example below.
On the NRCS state-level webpages, which I list below, you can view/download charts that show the coming and going of the snowpack over the season.
The chart below shows how the snowpack was stacking up in Colorado last season. The black line plots the current winter’s snowpack and the green line shows the 1991-2020 median. The dark blue and dark red lines chart the maximum and minimum readings during the 30-year period of record.
As a bonus, you can also plot projections for snowpack for the remainder of the season. In the April 4, 2024, chart below, the dashed lines show a variety of possible trajectories for the snowpack in the months ahead.
Below are links to the state-level sites. The first link is the overview page, followed by “site plots,” where you can view/download charts for individual SNOTEL stations, and then “basin plots,” where you can do the same for specific river basins.
California is included in the SNOTEL data discussed above, but the state also has its own monitoring system for the snowpack.
The California Cooperative Snow Surveys (CCSS) program, which was created by the state legislature in 1929, collects and analyzes data from more than 265 snow courses and 130 snow sensors located in the Sierra Nevada and Shasta-Trinity Mountains.
The graphic below from the California Department of Water Resources is from this page. A printable version of today’s conditions is on this page.
SnowTrax also offers more sophisticated data visualizations here, here and here.
Another page from the California Department of Water Resources offers additional data and graphics. For example, this page charts how the current year’s snowpack compares to recent years and the best/worst seasons in recent history.
Detailed Sierra Nevada reports
If you’d like to see very detailed maps of the Sierra snowpack, check out this page from researchers at the Institute of Arctic and Alpine Research at the University of Colorado Boulder. These experimental products provide “near-real-time estimates” of SWE at a resolution of 500 meters (1,650 feet, or about 0.3 miles). They’re based on recent cloud-free satellite imagery and on-the-ground data from snow pillows and other sources.
National Operational Hydrologic Remote Sensing Center
It’s a mouthful, but NOAA’s National Operational Hydrologic Remote Sensing Center is an essential source for snow data. NOHRSC’s interactive map offers a variety of snow-related data, including depth, temperature, density and melting. You can also select data for any day since 2002. Below is an example of the snowfall during 72 hours in southern Colorado and northern New Mexico.
Colorado’s snowpack supplies water to 19 other states downstream. If you’re looking for a detailed view of snow conditions in the state, check out SNODAS, which uses data from NOHRSC, satellites, planes and other sources to calculate daily SWE estimates for individual river basins. The project was funded by the Colorado Water Conservation Board and developed by the Open Water Foundation.
In the graphic below, I’ve highlighted the Animas River in southwest Colorado, which brings up a chart showing how the current year compares to past seasons and provides a snapshot of conditions in the basin.
The University of Arizona’s Snow Water Artificial Neural Network Modeling System (SWANN) uses a variety of data and machine learning to generate near real-time estimates for SWE and snow cover across the entire nation. SWANN estimates are also available back to the early 1980s. The SnowView dashboard lets you explore data on the snowpack, snow cover and precipitation while also providing satellite imagery and streamflow forecasts (more on the tool in this presentation). The April 1 map below shows the SWE estimates for the Intermountain West that were generated using SWANN.
Community Collaborative Rain, Hail and Snow Network (CoCoRaHS)
CoCoRaHS is a citizen-science effort that describes itself as “a unique, non-profit, community-based network of volunteers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow).”
Measurements from volunteers are plotted on an interactive map that has data available back to 1998. The image below shows 24-hour snowfall around Durango and Pagosa Springs.
As you’d expect, big cities have a lot more observations than rural areas. See this page for more about the project and how to sign up as a volunteer.
Data from CoCoRaHS is one of the inputs to this map from the National Centers for Environmental Information that tracks daily U.S. snowfall and snow depth.
Snow-related dashboards
Finally, several helpful websites aggregate data, maps and graphics from various sources, offering a quick overview of what’s happening with snowfall and the snowpack.
The Intermountain West Ski Dashboard, created by the Colorado Climate Center at Colorado State University, pulls together data on recent snowfall, short-term forecasts, weather hazards, snow depth, drought and more. Below is an example of a graphic showing that the vast majority of SNOTEL sites in Colorado were below the 50th percentile on January 1, 2024, with the vertical axis showing elevation and the different colors corresponding to different river basins:
The Intermountain West Climate Dashboard, created by the Western Water Assessment at the University of Colorado Boulder, is another useful round-up that focuses on Colorado, Utah and Wyoming. For example, the graphics below from the dashboard show SWE and projected streamflows in the Intermountain region.
Am I missing anything? Please feel free to suggest additions to this tip sheet by emailing me.
The Water Desk’s mission is to increase the volume, depth and power of journalism connected to Western water issues. We’re an initiative of the Center for Environmental Journalism at the University of Colorado Boulder.
Below-average snowpack at Park City ski area in Utah on March 23, 2022. Photo by Mitch Tobin, The Water Desk.
How is climate change affecting the West’s snowpack? What are the projections for the future?
Numerous scientific reports and studies in recent years have tried to answer these questions and others.
Below is an annotated bibliography of key scientific works related to climate change and the snowpack, focusing on the American West. At the bottom of the post is a list of recent journalism covering the issue.
Have a suggestion for a new study or story to add? Please contact me by email.
Publications from the IPCC, the United Nations body that assesses climate science, are a great place to start for a global overview of climate change. If you’re looking for insights into the cryosphere, check out this special report from the IPCC, which also covers the oceans.
Below are some of the (verbatim) conclusions from the summary for policymakers (see footnote 4 of this report for an explanation of the confidence-related terms).
“Over the last decades, global warming has led to widespread shrinking of the cryosphere, with mass loss from ice sheets and glaciers (very high confidence), reductions in snow cover (high confidence) and Arctic sea ice extent and thickness (very high confidence), and increased permafrost temperature (very high confidence).”
“Cryospheric and associated hydrological changes have impacted terrestrial and freshwater species and ecosystems in high mountain and polar regions through the appearance of land previously covered by ice, changes in snow cover, and thawing permafrost. These changes have contributed to changing the seasonal activities, abundance and distribution of ecologically, culturally, and economically important plant and animal species, ecological disturbances, and ecosystem functioning. (high confidence)”
“Since the mid-20th century, the shrinking cryosphere in the Arctic and high-mountain areas has led to predominantly negative impacts on food security, water resources, water quality, livelihoods, health and well-being, infrastructure, transportation, tourism and recreation, as well as culture of human societies, particularly for Indigenous peoples (high confidence).”
“Global-scale glacier mass loss, permafrost thaw, and decline in snow cover and Arctic sea ice extent are projected to continue in the near-term (2031–2050) due to surface air temperature increases (high confidence), with unavoidable consequences for river runoff and local hazards (high confidence).”
“Future land cryosphere changes will continue to alter terrestrial and freshwater ecosystems in high mountain and polar regions with major shifts in species distributions resulting in changes in ecosystem structure and functioning, and eventual loss of globally unique biodiversity (medium confidence).”
“Future cryosphere changes on land are projected to affect water resources and their uses, such as hydropower (high confidence) and irrigated agriculture in and downstream of high mountain areas (medium confidence), as well as livelihoods in the Arctic (medium confidence). Changes in floods, avalanches, landslides, and ground destabilization are projected to increase risk for infrastructure, cultural, tourism, and recreational assets (medium confidence).”
The special report has a chapter on high mountain areas, which includes the graphic below that summarizes the changes in regions around the world.
This congressionally mandated synthesis of research, known as NCA5, concludes there is “widespread consensus” that warming will “decrease the proportion of US precipitation that falls as snow, decrease snow extents, advance the timing of snowmelt rates and pulses, increase the prevalence of rain-on-snow events,” and transform the runoff that is vital for farms, cities and ecosystems.
The report concludes that climate change has already diminished the West’s snowpack, with warming global temperatures leading to earlier peaks and shorter seasons, especially at lower elevations and in areas closer to the coast. In areas where snow is the dominant source of runoff, the volume of water stored in the snowpack may decrease by more than 24% by 2050 under some emissions scenarios, with “persistent low-snow conditions emerging within the next 60 years,” according to the report.
NCA5 stresses that climate change’s reshaping of the water cycle and other impacts will exacerbate inequalities in U.S. society and pose a special threat to some marginalized communities.
Map “a” shows changes in the volume of the snowpack on April 1, a key date for water managers as they plan for the runoff season. About 93% of sites have experienced a decrease in April 1 snowpack since the 1950s, with the decline averaging about 23%. Map “b” concerns the timing of the snowpack’s peak, which has come nearly eight days earlier on average since 1982. Map “c” presents data on the length of the snow season, which has decreased by 18 days on average over the last four decades.
Researchers analyzed nearly 800 peer-reviewed studies, agency reports and other sources to assess the state of the science related to climate change and the hydrology of the Colorado River. Some of the key (verbatim) findings include:
“The period since 2000 has been unusually drought-prone, but even more severe and sustained droughts occurred before 1900.”
“There has been a substantial warming trend over the past 40 years; the period since 2000 has been about 2°F warmer than the 20th-century average, and likely warmer than at any time in the past 2000 years.”
“Decreases in spring snowpack and shifts to earlier runoff timing in many parts of the Upper Basin, as well as decreases in annual Colorado River flows at Lees Ferry, Arizona, have occurred in recent decades. These changes in hydrology can be linked, at least in part, to the warming trend.”
“There is still considerable uncertainty in the quantification of the relative roles of temperature, precipitation, antecedent soil moisture, dust-on-snow, and vegetation change in recent and ongoing variability and change in Upper Basin snowpack and streamflow.”
“Mainly due to the pervasive effects of warming temperatures on the water cycle, nearly all of the many datasets of climate change-informed hydrology and related studies show a strong tendency toward lower annual runoff volumes in the Upper Basin and the Lower Basin, as well as reduced spring snowpack and earlier runoff.”
Peer-reviewed scientific papers
Barnhart, T.B., N.P. Molotch, B. Livneh, A.A. Harpold, J.F. Knowles, and D. Schneider, 2016: Snowmelt rate dictates streamflow.Geophysical Research Letters, 43 (15).
Researchers examined how the speed at which snow melts affects streamflow and found that faster snowmelt causes higher and quicker peaks. “Earlier, slower snowmelt usually produces less streamflow than more rapid melt,” according to the paper. Ecoregions in the American West have varying sensitives to the change in snowmelt rate.
This paper uses tree-ring data to examine the Sierra Nevada snowpack over the past five centuries and concludes that “the 2015 low is unprecedented in the context of the past 500 years.” The scientists found the record-low snowpack corresponded with record-high temperatures in California from January to March 2015, noting that “the exacerbating effect of warm winter temperatures is stronger at low than at high Sierra Nevada elevations.”
In the bottom panel, the red line indicates the instrumental record, and the black line charts the reconstruction of Sierra Nevada snow water equivalent (SWE) on April 1. The horizontal dashed line shows the 2015 SWE value. The top panel zooms in on the 1930 to 2015 period.
This study finds that as more precipitation falls as rain rather than snow, flood sizes increase in a nonlinear fashion. Researchers found that the largest streamflow peaks driven by rainfall are more than 2.5 times the size of peaks driven by snowmelt. “Overall, as a higher percentage of precipitation falls as rain, increases in the size of rainfall-driven and ‘rain-on-snow’-driven floods have the potential to more than offset decreases in the size of snowmelt-driven floods,” according to the paper, which also notes there is a “large potential for continued regional warming to increase flood risk, even without changes in precipitation frequency, magnitude, or timing.”
Scientists found “widespread trends toward earlier snowmelt runoff related to warmer air temperatures,” with the timing significantly correlated with February to May air temperatures. In high-elevation basins in the West, streamflow timing was related to both temperature and precipitation.
The timing of snowpack melting varies greatly across the West, and this study seeks to understand why there are significant regional differences. “For 1 °C of warming, snowpack disappears 30 days earlier in some regions, whereas there is almost no change in others,” according to the study. Elevation, geographic location, precipitation patterns and the annual temperature cycle of a location impact the timing. Looking around the world, the researchers conclude that “the timing of snowpack disappearance will change most rapidly in coastal regions, the Arctic, the western United States, Central Europe and South America, with much smaller changes in the northern interiors of North America and Eurasia.”
This study examines 10 climate scenarios for the 21st century for snow, soil moisture and fuel moisture in the West. “A decline in mountain snowpack, an advance in the timing of spring melt, and a reduction in snow season are projected for five mountain ranges in the region,” according to the paper, which found “April 1 SWE losses by the 2080s of up to 81% for the Cascades and 76% for the Sierra Nevada mountains.” The diminished snowpack, combined with drier soils and fuels, is projected to increase wildfire potential across much of the region.
Researchers concluded that the snowpack shrunk in the U.S. and other places around the Northern Hemisphere from 1981 to 2020, but not everywhere on the planet. The researchers say warming is causing many watersheds to approach a tipping point they call a “snow-loss cliff,” where relatively small temperature rises could accelerate the shrinking of the snowpack in a “highly nonlinear” fashion.
This paper introduces a new measure—the Snow Storage Index—to analyze the changes to the hydrologic cycle. In Western North America, the annual snow storage index has decreased from 1950 to 2013 in 25% of mountainous areas due to “substantially earlier snowmelt and rainfall in spring months, with additional declines in winter precipitation.” The study projects further decreases in the index as warming causes earlier snowmelt and a shift from snowfall to rainfall.
Scientists found that atmospheric humidity plays a big role in controlling how the snowpack responds to warming temperatures, with the frequency and magnitude of winter melt events rising under higher-humidity conditions. “Increased winter melt in humid areas will require enhanced storage capabilities (reservoir, groundwater, etc.) to compensate for the decrease in snow storage and safeguard against increased winter flooding events,” the authors write. “Conversely, earlier and slower snowmelt in less humid areas could lower annual water yields due to sublimation losses and increased evapotranspiration, requiring updated water management strategies to conserve water in dry years.”
This paper identifies hotspots for “snow droughts” and shows that “eastern Russia, Europe, and the western United States experienced longer, more intense snow droughts in the second half of the period 1980 to 2018.” “Natural and human-driven factors (e.g., atmospheric circulation patterns, polar vortex movement, and Arctic warming) likely contribute to snow droughts,” according to the study.
The top panel shows the relative change in snow drought characteristics from 1980 through 2018. The bottom map shows the seven regions and an index of SWE used in the study.
In this study of the Sierra Nevada, the authors show that “even a 1.0 or 2.0 °C increase in average temperature leads to approximately a 20 to 40% increase in the likelihood of below average SWE.” The paper also found that the snowpack in the northern Sierra Nevada is more vulnerable to warming than in the southern part of the range.
Scientists examined both historical data and future projections for rain-on-snow events, which can cause severe flooding. The researchers conclude that rain-on-snow events will generally increase during November to March for most regions of Canada and the northwestern U.S., but southern regions may see a decrease due to reduced snow cover. The results also show a general increase in rain-on-snow events at higher elevations and a decrease at lower elevations.
This study investigates the rain-snow transition zone across the American West for both the late 20th-century climate and the projected climate in the middle of the 21st century. “At broad scales, these projections indicate an average 30% decrease in areal extent of winter wet-day temperatures conducive to snowfall over the western United States,” according to the study. The findings suggest that “many mountainous areas will be characterized by a mixed rain-snow regime in November, in contrast to the historic strongly snow-dominated precipitation regime.” The researchers also project that the likelihood of rain falling instead of snow will increase in March, April and May.
These maps show rain-dominated (blue), strongly snow-dominated (white), and rain-snow mix (pink to red) areas in the American West in the past (1979-2012) and future (2035-2065).
This analysis of long-term precipitation patterns in the American West finds an overall decrease in snowfall and an increase in rainfall from 1949 to 2004. The trend, which is due to rising temperatures, affects the volume of water stored in the snowpack, alters the timing of snowmelt and increases the risk of flooding in winter and spring. The trend was most pronounced across the region in March and in January near the West Coast. “Temperatures have warmed during winter and early spring storms, and, consequently, the fraction of precipitation that fell as snow declined while the fraction that fell as rain increased,” according to the paper.
This map depicts the change from water year 1949 to 2004 in winter SWE after removing the effects of precipitation trends. Three-quarters of stations experienced reductions due to warming.
This study (covered in a prior post) quantifies the contribution of snowmelt to runoff and projects how that will be altered by climate change. About 53% of runoff in the West originates as snowmelt, but warming will cause a shift from snow to rain, so the contribution of snowmelt to runoff is projected to decline to between 30.4% and 39.5%, under intermediate and high emissions scenarios. “Future runoff will be driven more by rainfall than snowmelt,” according to the study. “Since the western U.S. heavily relies on snowmelt stored in reservoirs to meet demands for water in the low flow season, reduced spring snowpack and earlier melt onset will likely put significant pressure on water supply in the late summer and fall.”
Researchers found that the shift from snow to rain will make it harder to predict droughts in the West. “By mid-century (2036–2065), 69% of historically snowmelt-dominated areas of the western United States see a decline in the ability of snow to predict seasonal drought, increasing to 83% by late century (2070–2099),” according to the study. Lower-elevation coastal areas will be most impacted by warming and generate more uncertainty in drought forecasts.
This graphic shows current conditions on the left, in which areas of abundant snowfall provide consistent observations that have high predictive power for subsequent streamflows. On the right, future conditions lead to less predictive power because some stations are no longer where snow is abundant, and snowmelt faces longer travel times, leading to more evaporative losses.
This study concludes that annual mean discharge for the Colorado River has been falling by 9.3% per degree Celsius of warming. The researchers say the decline is primarily driven by increasing evapotranspiration as the loss of snow cover increases the absorption of solar radiation. The snow cover acts like a “protective shield” that limits evaporative losses, but continued warming is projected to shrink the snowpack.
The 2018 paper updates the 2005 study, which found substantial declines in the West’s snowpack due to warmer temperatures. The more recent paper found that “over 90% of snow monitoring sites with long records across the western US now show declines, of which 33% are significant (vs. 5% expected by chance).” The researchers also report that “declining trends are observed across all months, states, and climates, but are largest in spring, in the Pacific states, and in locations with mild winter climate.” Average April 1 readings for SWE have declined 15% to 30% since the middle of the 20th century, which is comparable to the volume of Lake Mead, the West’s biggest reservoir.
Researchers found that 34% of monitoring stations in Western North America exhibited increasing winter snowmelt trends, a rate three times as large as the 11% of stations showing declines in SWE. Snowmelt trends are very sensitive to temperature and ongoing warming, while SWE trends are more sensitive to precipitation variability. The scientists also found that “the percentage of annual melt that occurs before 1 April is increasing by 3.5% per decade at 42% of the available stations” and argue that “this substantial and widespread rate of change implies a loss of seasonal storage of snow water resources in North American mountain water towers.”
These maps show stations with significant long-term changes to melting and the date of peak SWE. Map “a” shows the fraction of cumulative annual melt that has occurred by the date of annual maximum SWE, and map “b” shows the date of annual maximum SWE.
In this paper, scientists look at how climate change will impact rain-on-snow events and associated flood risks in Western North America. In a warming climate, rain-on-snow events are projected to become less frequent at lower elevations because of snowpack declines, especially in warmer areas like the Pacific maritime region. At higher elevations, however, these events are expected to become more common due to the shift from snow to rain. The greatest increase in flooding risk is projected in the Sierra Nevada, the Colorado River headwaters and the Canadian Rocky Mountains.
These maps show the average annual rain-on-snow events meeting the “flood potential” thresholds during the 2000 to 2013 period. Map “a” indicates historical conditions, map “b” depicts future conditions, and map “c” shows the difference between the two.
Researchers conclude that a “shallower snowpack melts earlier, and at lower rates, than deeper, later-lying snow-cover” and find that “the fraction of meltwater volume produced at high snowmelt rates is greatly reduced in a warmer climate.” The findings have implications for “soil moisture deficits, vegetation stress, and streamflow declines,” according to the study.
This study examines the decline in the West’s snowpack from 1950 to 1999 and finds that about half of the reduction is “the result of climate changes forced by anthropogenic greenhouse gases, ozone, and aerosols.” The study used 1,600 years of simulations to account for natural variability in the climate and also ruled out solar or volcanic activity causing changes to the snowpack.
Qin, Y., J.T. Abatzoglou, S. Siebert, L.S. Huning, A. AghaKouchak, J.S. Mankin, C. Hong, D. Tong, S.J. Davis, and N.D. Mueller, 2020: Agricultural risks from changing snowmelt. Nature Climate Change, 10 (5).
This global study identifies the regions and crops that are most dependent on snowmelt for irrigation and finds that the American West is one of the hotspots, along with the Tibetan Plateau, Central Asia, Western Russia and the Southern Andes. Under a 4°C warming scenario, reduced snowmelt will require some basins to find up to 40% of their irrigation demand in alternative sources.
This map shows which basins are most reliant on snowmelt runoff to supply irrigation for agriculture. The colors show the average share of irrigation surface water consumption met by snowmelt runoff, while the shading shows the average volume of surface water used for irrigation, normalized by basin area. “The darkest blue (most snow dependent) basins in high-mountain Asia (the Tibetan Plateau), Central Asia, western Russia, western US and the southern Andes are thus places where both irrigation and the share of irrigation demand met by snowmelt runoff are large,” according to the study.
This study projects future changes in the timing of snowmelt-driven runoff in the Western United States. Rising greenhouse gas emissions could lead to 3°C to 5°C increases in seasonal temperatures that cause snowmelt-driven runoff to occur as much as two months earlier. “These large changes result from an amplified snow-albedo feedback associated with the topographic complexity of the region,” the authors write.
This review paper discusses how climate change is decreasing snowpacks around the world and warns of “potentially catastrophic consequences on water resources, given the long-held reliance on snowpack in water management.” Across the West, SWE declines of about 25% are expected by 2050, and it may be “~35–60 years before low-to-no snow becomes persistent if greenhouse gas emissions continue unabated.”
The Water Desk’s mission is to increase the volume, depth and power of journalism connected to Western water issues. We’re an editorially independent initiative of the Center for Environmental Journalism at the University of Colorado Boulder.
