Rittger

The data is in: Colorado’s snowpack is lagging behind the 21st century average in 2025

Gabe Allen — Thu, 10 Apr 2025 16:30:00 +0000

The data is in: Colorado’s snowpack is lagging behind the 21st century average in 2025 Gabe Allen Thu, 04/10/2025 - 10:30

Gabe Allen

A new modeling tool from INSTAAR provides weekly snow-water equivalent estimates for the entire Western US.

Last week, INSTAAR’s Mountain Hydrology Group released its fifth near-real-time report on snow-water equivalent (SWE) in the Western US in 2025. In essence, the report provides a snapshot of how much water is stored in snow on the landscape—water that will feed our rivers and streams in the months to come.

The end-of-March report is of particular interest for water managers in the West, because it arrives around the time that snow in the region reaches its peak. Last week’s report will help managers adjust plans for the spring, summer and fall.

“It helps inform how much water storage they might have and when that might come down into their reservoirs,” INSTAAR PhD student and report co-author Emma Tyrrell said.

Other tools for visualizing the snowpack exist, such as the Natural Resources Conservation Service Snow and Water Interactive Map, which plots various SWE-measuring stations. But, the Mountain Hydrology Group’s reports take a uniquely comprehensive approach. The team combines multiple data sources and modeling tools to estimate the amount of water stored in snow across the entire landscape.

The skinny

A map showing the percent of the long-term (2001 to 2021) average snow-water equivalent in major regions of the Western United States as of March 31, 2025.

Here in the Front Range, the report shows SWE totals lagging behind the 2001 to 2021 average. However, the overall trend doesn’t hold at all elevations. While the plains and foothills have less snow than average, many mountainous areas, like the headwaters of the Colorado River, sport average or higher-than-average snowpacks.

“Where you might go skiing, we’re seeing around 100% of normal,” Tyrrell said.

If you zoom out to the entire Western US, the report shows some anecdotal regional trends. The Desert Southwest has had a dry winter, with many regions dipping below 50% of average SWE and some in the single digits. On the other hand, a pocket of mountainous regions in the Northwest, stretching from Western Wyoming to Oregon, is experiencing an unusually robust spring snowpack.

“We’re seeing a somewhat typical north to south gradient during a La Niña cycle,” senior professional research associate Leanne Lestak told INSTAAR.

An experiment, a product

The Mountain Hydrology Group, led by INSTAAR faculty fellow Noah Molotch, has been producing SWE reports for the Sierra Nevada Mountain region in California since 2012. There, water managers and river forecasters have come to rely on the reports.

“We work really closely with the California Department of Water Resources." Lestak said. “The hydrologic engineers use our data in their forecasts, and they really rely on what our reports have to say. It’s such an honor to work with these folks.”

The west-wide report is a newer endeavor—the group put out the first of its biweekly reports this February. Like the Sierra Nevada reports, the west-wide reports draw on a mix of satellite imagery, remote snow sensors and statistical modeling to arrive at its estimates. When they can, the team also calibrates their results by comparing them to “Airborne Snow Observatories,”—intermittent snow surveys conducted via manned aircraft in Colorado and elsewhere.

“We consider them a ground truth,” Tyrrell said. “It’s a patchwork of data that we can use to bias correct.”

While the methodology that the CU team uses for the Sierra Nevada reports has been refined by years of tweaking, the west-wide methodology is still new—it’s an experimental product. It will take a few years for the team to refine the model and build trust with stakeholders.

Locally, the project has already garnered some interest.

“Denver Water and other local cities are interested,” Lestak said. “There aren’t a lot of products here on the Front Range.”

We may have reached peak SWE for 2025 here in the west, but the Mountain Hydrology Group will keep issuing reports until mid summer. All the while, they will work to refine their tools.

If you have questions about this story, or would like to reach out to INSTAAR for further comment, you can contact INSTAAR Communications Specialist Gabe Allen at gabriel.allen@colorado.edu.

A new modeling tool from INSTAAR provides weekly snow-water equivalent estimates for the entire Western US. It has already caught the attention of local and regional water managers.

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International research collaboration uncovers key driver of Himalayan glacier melt

David J Lubinski — Wed, 12 Feb 2025 03:01:58 +0000

International research collaboration uncovers key driver of Himalayan glacier melt David J Lubinski Tue, 02/11/2025 - 20:01

Gabe Allen

Pollution-laden dust storms are depositing black carbon on the Himalayas. New research from INSTAAR’s Karl Rittger and collaborators reveals the process.

Regional pollution is speeding up snow melt in the Indian Himalayas. That’s according to a new study from an international group of scientists including Indian Institute of Technology Madras civil engineering PhD student Amit Singh Chandel and INSTAAR research associate Karl Rittger.

Three of the four largest river basins in the world lie in this region. Understanding this snowmelt is a key question.
- Chandan Sarangi

The study, published in the Journal of Geophysical Research: Atmospheres, reveals how dust storms pick up black carbon from heavily-polluted areas and deposit it in the mountains. Black carbon darkens the ice and snow, causing it to melt faster.

It’s a key insight into a persistent problem. Dwindling ice in the Himalayas has long troubled researchers and decision makers in southern Asia. Nearly two billion people rely on the water produced by Himalayan snowmelt, and glacier loss could lead to water shortages and an increase in extreme floods.

“Three of the four largest river basins in the world lie in this region,” coauthor Chandan Sarangi said. “Understanding this snowmelt is a key question.”

The new study is the result of collaboration across scientific disciplines and international borders. The seeds were planted a few years ago. Sarangi’s lab had already published numerous mathematical models mapping perennial dust storms in Northern India. And they knew that black carbon was getting into the dust somewhere along the way.

In order to paint a clearer picture, Sarangi looked to pair his modeling work with long-term measurements from the field. That’s how he found co-author Rakesh Hooda, a senior research scientist at the Finnish Meteorological Institute. Hooda previously collected nine years of atmospheric measurements at a site in the Himalayan foothills.

Hooda’s data, paired with Sarangi’s models, revealed two distinct types of storms. The first type brews in the deserts of western India and Pakistan and travels east at low elevations. These storms mix with pollution from the heavily-populated Indo-Gangetic Plains before reaching the Himalayas.

You get a darkening of 26% versus 58%. The polluted dust events have double the impact. It’s still a human-induced impact, it’s just not a climate change impact.
- Karl Rittger

The second type of storm starts in the Saharan Desert and travels at higher altitudes. These storms pick up very little pollution.

The new model told the researchers where the dust storms were coming from and what was in them. Now the question was how the storms impact snow and glaciers.

That’s where Rittger came in. In previous research, he had developed a model that could tease apart contributing factors to snow-darkening using satellite imagery. The team applied Rittger’s methodology to the dust storm models and once again validated the findings with on-the ground data.

The results were clear. The storms with high concentrations of pollutants melted more snow.

“You get a darkening of 26% versus 58%.” Rittger said. “The polluted dust events have double the impact.”

Previous research on diminishing glaciers in the Himalayas has often focused on global warming, but the new findings reveal a second, more local cause. To Rittger, it’s a good reminder to look for regional environmental problems that might mimic or coexist with global ones.

“It’s still a human-induced impact, it’s just not a climate change impact,” he said.

The success of this study has all of the co-authors thinking about next steps. Rittger hopes to one day expand his Snow Today website, which provides automated readouts of snow characteristics in the Western US, to Asia. Sarangi hopes to establish more field sites.

“We need more measurements to characterize the aerosols reaching the Himalayas.” He said. “It’s increasing every day.”

Site for measuring aerosol microphysical and optical properties during dust storms, Mukteshwar, Uttarakhand, India. This central Himalayan foothills location is representative and remote, with minimal local emissions. Photo from Chandan Sarangi (IIT Madras).

If you have questions about this story, or would like to reach out to INSTAAR for further comment, you can contact Senior Communications Specialist Gabe Allen at gabriel.allen@colorado.edu.

Pollution-laden dust storms are depositing black carbon on the Himalayas. New research from INSTAAR’s Karl Rittger and collaborators reveals the process.

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Quenching the arid West with record snowfall: The tools behind snow data (NSIDC)

Anonymous — Sat, 23 Dec 2023 06:10:08 +0000

Quenching the arid West with record snowfall: The tools behind snow data (NSIDC) Anonymous (not verified) Fri, 12/22/2023 - 23:10

The 2023 winter brought record snowfall to California, but getting accurate snow depth data over a wide area is not easy. Read about the challenges of garnering snow data and the tools behind the data. Among the experts consulted is Karl Rittger (INSTAAR Fellow & NSIDC Affiliate), who leads the Snow Today project, visualizing and analyzing snow conditions across the Western U.S.

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Wildfires are increasingly burning California’s snowy landscapes and colliding with winter droughts to shrink California’s snowpack (DRI)

Anonymous — Thu, 02 Feb 2023 22:25:21 +0000

Wildfires are increasingly burning California’s snowy landscapes and colliding with winter droughts to shrink California’s snowpack (DRI) Anonymous (not verified) Thu, 02/02/2023 - 15:25

Desert Research Institute

A new study published in Geophysical Research Letters shows that midwinter dry spells lead to dramatic losses of winter snowpack in burned areas of California. INSTAAR Karl Rittger participated in the study, led by scientists from the Desert Research Institute.

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Snowpack improves as atmospheric river pours on Rocky Mountains (8NewsNow)

Anonymous — Tue, 24 Jan 2023 22:02:52 +0000

Snowpack improves as atmospheric river pours on Rocky Mountains (8NewsNow) Anonymous (not verified) Tue, 01/24/2023 - 15:02

Greg Haas

Snowpack levels in the Upper Colorado River Basin have improved over the last two weeks, fueled by an atmospheric river carrying moisture from the Pacific Ocean. Karl Rittger is quoted extensively in this 8NewsNow story about Colorado snowpack and its impact on drought.

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