This winter was ; as a result, many snowy, alpine areas have seen bouts of winter rainfall where there would ordinarily only be snow. These unusual weather patterns have contributed to an abysmal ski season, but they can also set the stage for dangerous avalanches. At temperatures close to freezing, precipitation can fall as rain but freeze when it hits the snow, forming an icy crust. Snow that accumulates on top of that crust is unstable and prone to abrupt slides, causing an avalanche that can close down a major highway in moments, endanger backcountry skiers and more.

Avalanche experts in Western Washington know how to manage the risks associated with rain-on-snow events, but many of their counterparts in colder regions like Eastern Washington, Idaho and Montana are less familiar with these dynamics. New research from the 91̽�� shows that as winters in these regions warm, their snowpacks may come to resemble those of maritime areas, with more rain-on-snow events, icy crusts and complex avalanche forecasting.��

The findings in ARC Geophysical Research.

“This winter’s warmth is a harbinger,” said lead author , a 91̽��graduate student of civil and environmental engineering. “We know that temperatures will keep rising, and our work is a red flag for cooler regions of the greater Pacific Northwest, such as Idaho and Western Montana, that aren’t used to dealing with ice crusts and their resulting avalanche problems.”

The study is part of a larger effort to understand the structure of snow as it accumulates, which has implications for weather and avalanche forecasting, wildlife dynamics and more.��

“Snow scientists are pretty good at measuring snow depth and volume,” said senior author , a 91̽��professor of civil and environmental engineering. “We’re also pretty good at figuring out how much water you get if all that snow melts. But our models aren’t as good at representing snow structure, such as layers of different densities and crystal types that increase avalanche risks. And we really want to know how the structure of snow changes as the climate changes. That’s a tricky question that no one has tackled, particularly for rain-on-snow conditions.”

To dig into that question, the researchers studied how warming influences ice layer formation in seasonal snowpacks. First, they collected temperature and precipitation data captured by 53 monitoring stations across the Pacific Northwest for the past 25 years. They used a computer model to identify days when ice layers likely formed at each location. They then checked the model against real-world measurements at one of the locations — a station at Snoqualmie Pass — and found that the model matched the measurements with 74% accuracy.

Finally, they used the same model to simulate those same 25 winters at 2 C and 4 C warmer than they were, and looked for changes to the number of ice crusts across the region. , the Pacific Northwest is expected to warm by 2 C to 5 C by 2050 as compared to pre-2000 temperatures.

The results were split regionally by the Cascade mountains. In colder, inland parts of the Pacific Northwest — places like Eastern Washington, Idaho and Montana — higher temperatures created more rain-on-snow days and more avalanche-prone ice layers. Locations in the warmer, maritime Cascades saw the opposite effect: Higher temperatures created slush instead of ice, potentially reducing the avalanche risk associated with ice crusts.��

The predicted snowpack changes may also impact wildlife behavior. Some foraging mammals, such as reindeer, dig down into the snow in search of food and may have a hard time breaking through an icy crust. Conversely, firm ice might provide a better running surface for animals fleeing predators. Specific regional effects will require additional study.

What’s clear now is that those who work or play in avalanche terrain in broad swaths of the Pacific Northwest — and even beyond — may need to adjust to a new set of risk factors.

“I’d love to see this shared with avalanche forecasters widely, both as a call to action and as a way to help them understand what their snowpack might look like in the future,” Alden said.

, the director of geospatial science at Audubon Alaska and former doctoral student of environmental and forest sciences at the UW, is a co-author.

This research was funded by the NASA Interdisciplinary Research in Earth Science program and the 91̽��Program on Climate Change’s Graubard Fellowship.

For more information, contact Alden at cdalden@uw.edu.

As climate change nudges weather in the eastern Cascades in extreme and volatile directions, forest managers in the region have a lot to juggle. Hotter, drier summers are contributing to bigger and more frequent wildfires. Meanwhile, warmer winters may cause the Cascades to lose 50% of its annual snowpack over the next 70 years. Mountain snow supplies the Yakima River Basin with 75% of its water supply, making it a crucial reservoir for both nature and agriculture . Less winter snow also leads to drier and more fire-prone forests in the summer.

To encourage fire resilience, forest managers use tried-and-true tools like controlled burning and the selective felling of trees to thin out the forest. Both methods remove fuel and help return forests to historical conditions — but less is known about their impact on snowpack.

To address this knowledge gap, a team of researchers at the 91̽�� and The Nature Conservancy (TNC) embarked on an ambitious, multiyear study of snowpack along Cle Elum Ridge, an area of the eastern Cascades in the headwaters of the Yakima River Basin. The group experimentally thinned the forest to varying degrees in a roughly 150-acre area. Then, they measured the amount and duration of snowpack during the winter of 2023 and compared it to a previous winter before the forest treatment.��

The results were encouraging: Forest thinning efforts increased snowpack by 30% on north-facing slopes and by 16% on south-facing slopes. Thinning aided snowpack the most where it created a patchwork of gaps in the forest rather than a more even density; gaps of 4-16 meters in diameter seemed to be the “sweet spot” for snow.��

The research points toward more refined forest management practices that can optimize for both wildfire resilience and snowpack.

in Frontiers in Forest and Global Change.

“At its core, this research shows that reducing wildfire risk and protecting water resources don’t have to be competing goals,” said lead author , a postdoctoral researcher at the University of Alaska who completed this work as a 91̽��doctoral student of civil and environmental engineering. “That’s genuinely good news for a place facing both growing wildfire threats and increasing water vulnerability. So much of the climate conversation focuses on loss, which makes findings like this especially meaningful.”

Predicting snowpack in forested areas, especially those at higher altitudes, hinges on understanding how much snow reaches the ground and how much lands in the forest canopy. Snow on the ground is more likely to stick around through the season, whereas snow in the trees may either melt or sublimate back into water vapor. In either case, it wouldn’t add to the reservoir of water that melts in the spring and summer.�� 

“Trees intercept snow and so can reduce snowpack, but trees also shade snow and so can retain snowpack,” said senior author , a 91̽��professor of civil and environmental engineering. “The dominant effect depends on winter temperatures, and the Cascade crest near Cle Elum is right on the border where the effect flips from trees decreasing snow to trees saving snow.” 

found that natural gaps in the forests of the eastern Cascades accumulated more snow. This, combined with other research, gave the team reason to hope for a positive connection between forest thinning and snowpack, though it wasn’t a sure thing. have found that open areas elsewhere in the Western U.S. saw reduced snowpack.

Thus, it was time for a direct — and complex — study of managed forests.

Researchers picked Cle Elum Ridge for the work, where TNC’s forest managers were planning thinning treatments to improve forest health and wildfire resiliency. The orientation of the ridge allowed them to compare north- and south-facing slopes — southern slopes in the region see more sunshine and less snow retention on average. From October 2021 to September 2022, the researchers worked with TNC’s forest managers and local contract loggers to remove trees on both slopes in a gradient, from no thinning to extensive. The team also set up time-lapse cameras at several strategic points to measure snow depth over time.

Then, they waited for snow to fall.

By March 2023, the area was close to its peak snowpack, and the team returned with staff and equipment from the 91̽�� (RAPID). The RAPID crew flew a specialized drone that generated a detailed 3D map of the study area using a laser-mapping technology called lidar.��

By comparing the new 3D map and timelapse imagery to lidar data captured before the forest treatment, the team was finally ready to calculate two things: the change to the forest structure, and its effect on the snowpack.

Across the whole study area, the team found that thinning helped the forest recover 12.3 acre-feet (or about four million gallons) of water in the form of snow per 100 acres on north-facing slopes, and 5.1 acre-feet (or about 1.5 million gallons) per 100 acres on south-facing slopes.��

As expected, areas where the thinning opened gaps in the canopy were most effective at restoring snow storage that had been previously lost to environmental degradation and climate change. Gaps of 4-16 meters in diameter seemed to retain the most snow, though there were few gaps larger than 16 meters to evaluate.

One surprising result: The way forest managers thin forests doesn’t reliably create gaps. Forest managers map out their reductions using the density of trunks in an area, not canopies, as their primary measurement.

“Imagine a group of 100 people all holding umbrellas in the rain,” said co-author , director of the 91̽��Climate Impacts Group. “They’re standing close enough together that their umbrellas overlap, so none of the rain hits the ground. If you remove 10 of the umbrellas randomly, you’d still have plenty of coverage overall. But, if you remove 10 umbrellas that are right next to one another, you create a gap in the umbrella ‘canopy,’ and you get a 10% increase in the amount of rain that hits the ground.”

That realization adds a nuance to the findings. It’s likely that forest thinning can benefit both wildfire and snowpack resilience at the same time, but only if managers keep canopy gaps in mind.��

“One thing we all learned was that snow people and tree people speak different languages,” Lumbrazo said. “Different experts look at totally different variables to help them decide whether or not to cut down a single tree. So an important goal is to get everyone speaking the same language. And I think this paper is one step towards better communication.”

Overall, the results suggest practical changes to forest management practices in the eastern Cascades. For example, managers might consider more tree-thinning on north-facing slopes, since snowpack gains may be greater there. With further research, these learnings may also extend to other regions in the Pacific Northwest.��

The work could also aid collaboration between forest managers and hydrologists at a time when the region needs all the water it can get.

“As we lose snowpack, everything becomes really squeezed,” said co-author , a senior aquatic ecologist at TNC who earned her doctorate in aquatic and fishery sciences at the UW. “We are currently in our third consecutive year of water restrictions in the Yakima River Basin, and are staring down one of the lowest snow years on record. However, our research shows that the treatments currently used for restoring fire resilient forests are compatible with the forest structure needed for supporting water security. And in a world where climate change is reducing water supplies and increasing wildfire severity, we are pleased to report that the same forest treatments can support both goals.”

Co-authors include , a former 91̽��graduate student of civil and environmental engineering; , a former 91̽��undergraduate student of atmospheric and climate science; , a data processing specialist at the 91̽��RAPID facility; and , director of Forest Conservation and Management at The Nature Conservancy.

This research was funded by The Washington Department of Natural Resources, The Nature Conservancy and the National Science Foundation.��

For more information, contact Lundquist at jdlund@uw.edu, Dickerson-Lange at dickers@uw.edu or Howe at emily.howe@tnc.org.��

The Colorado River and its tributaries . Much of this water comes from the snowpack that builds up over the winter and then melts each spring. Every year in early April, water managers use the snowpack to predict how much water will be available for the upcoming year.

But since 2000, these predictions have been incorrect, with the actual streamflow being consistently lower than the predicted streamflow. That’s left water managers and researchers flummoxed — where’s the water going?

The problem lies with the lack of rainfall in the spring, according to new research from the 91̽��. The researchers found that recent warmer, drier springs account for almost 70% of the discrepancy. With less rain, the plants in the area rely more on the snowmelt for water, leaving less water to make its way into the nearby streams. Decreased rain also means sunny skies, which encourages plant growth and water evaporation from the soil.

The researchers Aug. 16 in Geophysical Research Letters.

“The period of time when we were wondering, ‘Oh no, where’s our water going?’ started around the same time when we saw this drop in spring precipitation — the beginning of the ‘Millennium drought,’ which started in 2000 and has been ongoing to the current day,” said lead author , a 91̽��doctoral student in the civil and environmental engineering department. “We wanted to focus on the cascading consequences of this. Less springtime rain means you likely have fewer clouds. And if it’s going to be sunny, the plants are going to say, ‘Oh, I’m so happy. The snow just melted and I have a ton of water, so I’m going to grow like gangbusters.’ This research really centers the importance of studying the whole snow season, not just when the snowpack is the deepest.”

Hogan and senior author , a 91̽��professor of civil and environmental engineering, studied this phenomenon as part of a . At first, the researchers wondered if the snowpack was decreasing because the snow was simply turning into water vapor — a process called sublimation. But the team , meaning something else was the main culprit.

“There are only so many possible culprits, so I started to compare things that might be important,” Hogan said. “And we saw that springtime changes are a lot more exaggerated than they are in other seasons. It’s this really dramatic shift where you’re going from feet of snowpack to wildflowers blooming over a very short amount of time, relatively speaking. And without spring rains, the plants — from wildflowers to trees — are like giant straws, all drawing on the snowpack.”

The researchers looked at springtime changes in 26 headwater basins at various elevations in the Upper Colorado River Basin. To paint a picture of what was happening at each basin over time, the team used a variety of datasets, including streamflow and precipitation measurements dating back to 1964. The researchers then modeled how much water the plants at each basin would likely consume.

“We make an important assumption in the paper,” Hogan said. “We assume that the plants have an unlimited amount of water even with less-than-average precipitation, because they have access to snowmelt.”

All the basins the team studied showed reduced streamflow without springtime rain. But basins at lower elevations had an even more pronounced deficit in streamflow. This is because the snow at these basins is likely to melt earlier in the season, giving the plants more time to grow and consume the snowmelt, the researchers said.

Now that spring rain has been identified as the main culprit, the researchers are working to further refine their understanding of what’s happening during this season. For example, one project is investigating whether residual patches of snow are acting as mini-reservoirs that can provide a constant stream of water to nearby plants.

Regardless, the longer the Millennium drought continues, the more these results will affect the water calculations that happen each April.

“April is when everybody wants to know how much water is in the snowpack each year,” Lundquist said. “But the problem with doing these calculations in April is that obviously spring hasn’t occurred yet. Now that we know spring rain is actually more important than rain any other times of the year, we’re going to have to get better at predicting what’s going to happen rainwise to make these April predictions more accurate.”

In this video, Jessica Lundquist gives more background on this project

This research was funded by the National Science Foundation, the Sublimation of Snow Project and the Department of Energy Environmental System Science Division (the Seasonal Cycles Unravel Mysteries of Missing Mountain Water project).

For more information, contact Hogan at dlhogan@uw.edu and Lundquist at jdlund@uw.edu.

As climate change warms the planet, weather patterns are likely to shift. Even the consistency of snow — how fluffy it is, for example — could change.

, a wildlife ecologist and 91̽�� associate professor in the School of Environmental & Forest Sciences, wants to know how these changing conditions will affect how predators hunt prey.

“When you wear snowshoes in deep snow, you stay on top of the snow. But if you take the snowshoes off, you might go in up to your waist. Certain species, such as wolves and lynx, have adapted to deep snow conditions because their feet act like snowshoes,” Prugh said. “But their prey, such as caribou and moose, are heavier and have hooves instead of paws, so they sink in more. As climate change is making things warmer and changing the amount of precipitation, it’s going to affect how deep and hard the snow is. And that’s going to affect how deep the animals are sinking into the snow. Few scientists have looked at this before.”

To answer this question, Prugh needed a snow expert. She teamed up with , a 91̽��professor of civil and environmental engineering. Together with a group of researchers, the two measured snow properties that led to a “danger zone,” where prey would sink but predators would not. In a recent paper, the team defined .

The first step was to figure out how to measure changes in the snow that would affect animals’ ability to stay on top of the snow.

“Imagine having a snow fort — you’ve got this cave under the snow and it has a roof. And when people run on top of your snow fort, you hope it doesn’t collapse on you, right? This is what we are trying to measure: the strength of the snow to support itself against collapsing,” Lundquist said. “But snow is such a dynamic thing. It’s not even one phase; you can’t call it a solid, liquid or gas. It’s all of the above, and that makes snow really fun to study.”

The researchers used snow density as a proxy for its strength. Denser, more tightly packed snow, they reasoned, would be more likely to hold up an animal, compared to light, fluffy “powder skiing” snow.

To test this theory, the team traveled through Denali National Park and the Methow Valley via snowmobile or on cross-country skis in search of animal prints in the snow. Upon finding tracks, the researchers could then investigate the density and other properties of the surrounding snow.

Both Prugh and Lundquist agreed that one of the best parts of the collaboration was being able to learn from each other — Prugh learned to appreciate different types of snow, and Lundquist learned how to identify different animal tracks. The researchers also enjoyed working outside.

“There’s this where Calvin’s standing in front of his class holding a box of water. And he says, ‘this was a snowflake outside,'” Lundquist said. “It’s unique and exquisite, but when you bring it into the classroom, it melts. The science is outside. You cannot bring snow inside and have the same characteristics as the snow outside.”

For more information, contact Prugh at lprugh@uw.edu and Lundquist at jdlund@uw.edu.

Spring break can be a good time for ski trips — the days are longer and a little warmer. But if people are booking their spring skiing trips the fall before, it’s hard to know which areas will have the best snow coverage later in the season.

Researchers who study water resources also want to know how much snow an area will get in a season. The total snowpack gives scientists a better idea of how much water will be available for hydropower, irrigation and drinking later in the year.

A team led by researchers at the 91̽�� has found that in some western states, the amount of snow already on the ground by the end of December is a good predictor of how much total snow that area will get. This prediction works well in northern states such as Alaska, Oregon and Washington, as well as in parts of Utah, Wyoming and Colorado. Other states, such as California, Nevada, New Mexico and Arizona, were harder to predict — these regions either had too much variation in their weather patterns and/or got the most of their precipitation after December.

The researchers Sept. 12 in Geophysical Research Letters.

“The main thing water managers are asking for — aside from making it snow more, which is usually everyone’s first request — is longer lead-time forecasts,” said senior author , 91̽��professor of civil and environmental engineering. “These are hard predictions to make. We’re fairly good at long-term average forecasts: what will happen 50 years from now. And we can do short-term forecasts: what will happen less than a week from now. But as for what’s going to happen in the next three to four months, that’s been kind of a no-go zone. It was really interesting to find that the amount of snow on the ground by the end of December ended up being a good predictor of peak spring snow.”

To look for trends, the team collected data from a across the western U.S., including Alaska. The researchers analyzed air temperature and accumulated precipitation from 2001 to 2022 for 873 sites. Then the team compared accumulated snow by the end of December (fall snow) to the maximum amount of snow accumulated over the entire winter-spring season (peak season snow).

There were a few different reasons for why fall snow levels predicted peak season snowpack levels. Some areas, such as Alaska, simply receive most of their snow before January. This means their early season snow is close to their peak season snow.

In other places, including Interior Alaska, northeast Utah and southwestern Wyoming, the weather patterns are such that above-average snowfall earlier in the season indicates above-average snowfall is also likely later in the season.

Cooler air temperatures also helped with predictability. In northern states — such as Alaska, Washington and Oregon — or in places at higher elevation, snow on the ground in the fall was less likely to melt between storms because the air remained cool. That means this snow will stick around and add to the total snowpack.

“Another really interesting pattern happens in Oregon and Washington,” Lundquist said. “We get mixed rain and snow all along the west slope of the Cascades. This ‘wintry mix’ is so close to freezing that it could freeze or melt when it hits the ground. If you have above-average snowpack early in the year, then the wintry mix will stick to that snowpack and add to it. But if you have a below-average snowpack, that wintry mix is more likely to melt that snowpack and actually decrease it.”

When it comes to how climate change will affect which areas are predictable, the results are mixed, Lundquist said. Places that are farther north or at higher elevation are colder to start with, meaning they might not see much change.

But some weather patterns are shifting north. Areas where the prediction works now — such as northern Oregon — might go the way of California, having weather that’s too variable for any prediction.

It’s going to be important to continue tracking these trends, Lundquist said.

“These snow sensors are in long-term stations, so it’s easy to get the most recent data every year,” Lundquist said. “And then it’s just a simple analysis to predict which areas will likely have the largest snowpack. Though, as my family reminds me, it unfortunately does not let me predict powder days.”

Additional co-authors are , 91̽��professor of environmental and forest sciences; at the National Oceanic and Atmospheric Administration; and at The Ohio State University. This research was funded by NASA. Lundquist wrote this paper during sponsored by the 91̽��ADVANCE Center for Institutional Change.

For more information, contact Lundquist at jdlund@uw.edu.

The snow that falls in the mountains is good for more than just skiing, snowshoeing and breathtaking vistas. The snowpack it creates will eventually melt, and that water can be used for hydropower, irrigation and drinking water.

Researchers want to predict how much water we will get later in the year based on the snowpack. But in forested regions, the trees impact the calculations. When falling snow is intercepted by trees, it sometimes never makes its way to the ground, and the current models struggle to predict what will happen.

To improve the models and investigate what happens to this intercepted snow, 91̽�� researchers created a citizen science project called . Participants viewed time-lapse photos from Colorado and Washington and labeled photos taken when trees had snow in their branches. This information provided the first glimpse of how snow-tree interactions could vary between climates and how that could affect predictions of summer water supplies.

The team May 18 in AGU Water Resources Research.

“We, as skiers or snow enthusiasts, know that the snow in Colorado compared to Washington is really different. But, until now, there hasn’t been an easy way to observe how these differences play out in the tree canopy,” said lead author , a 91̽��doctoral student studying civil and environmental engineering. “This project leverages volunteers to get some hard data on those differences. Another benefit is that it introduces our volunteers to how research works and what snow hydrology is.”

There are three possible scenarios for snow that’s been caught by trees. It could fall to the ground as snow, adding to the current snowpack. It could be blown away and turn to water vapor, therefore not adding anything to the snowpack. Or the snow could melt and drip to the ground, which, depending on the conditions, may or may not add to the total amount of water in the snowpack.

One current issue with the mathematical models that describe these processes is that researchers don’t know the timing — over the course of a year, how often is there snow in the trees, and what happens to it? — and how this timing varies in different climates.

But time-lapse cameras can record what’s happening in remote locations by taking photos every hour, every day for years, creating a huge dataset of images.

That’s where the citizen scientists come in. Snow Spotter shows volunteers a photo, with the question: “Is there snow in the tree branches?” Volunteers then select “yes,” “no,” “unsure” or “it’s dark” before moving on to the next photo.

Using Snow Spotter, a total of 6,700 citizen scientists scanned 13,600 images from a number of sites across the western United States. The team focused on four sites for this study: Mount Hopper, Washington; Niwot Ridge, Colorado; and two different sites in Grand Mesa, Colorado.

“When the project started, I don’t think anybody really knew how successful it was going to be,” said Lumbrazo, who is currently doing research in Norway as part of the . “But citizen scientists were processing it so fast that we kept running out of images for people to classify. We’ve received feedback that this task is really relaxing. Citizen scientists can pull up these photos in the Zooniverse app and they can just sit on the couch and click through really fast.”

Each photo had between nine and 15 different volunteers classify it, and the volunteers agreed between 95% and 98% of the time. From there, the researchers could piece together what snow in the trees looked like over the course of the year for each site.

“Our data physically shows the difference in the snow,” Lumbrazo said. “You can see how the snow in Washington just becomes cemented in the canopy and never leaves, which is how it feels when you ski that snow. As opposed to the snow in Colorado where you get frequent snowfall, but it’s blowing away. It’s dry and dusty.”

The researchers used this dataset to evaluate current snow models. One limitation, however, is that right now the team only knows when snow is present in the trees. This method doesn’t say how much snow is in the trees, another component needed to make the models even better.

“But a limitation that does not exist is the number of citizen scientists who are willing to process these images,” Lumbrazo said. “We’ve signed off on countless volunteer hours for students, and they even end up having some great discussions about certain images and it becomes more of a scientific conversation.”

In addition, the dataset generated by these volunteers could be used to train a machine learning algorithm to classify images in the future, the team said.

The researchers are working to expand their image dataset to include photos from around the world so that they can continue learning about how different climates and precipitation patterns affect the snowpack, which will also help make the models more accurate.

Additional co-authors are and , both of whom completed this research as 91̽��civil and environmental engineering doctoral students; and and , both 91̽��professors of civil and environmental engineering. Snow Spotter was created by , who started this project as a 91̽��undergraduate student studying civil and environmental engineering. This research was funded by the National Science Foundation and a Steve and Sylvia Burges Endowed Presidential Fellowship.

For more information, contact Lumbrazo, who is currently on Central European Time, at lumbraca@uw.edu.

Grant number: CBET-1703663

This year’s 91̽��awardees are from the College of the Environment and the College of Engineering, focused on topics that include ocean wave dynamics, the behavior of glaciers and how predator-prey interactions can influence wildfires. NASA awarded about 120 fellowships for this year’s Future Investigators in NASA Earth and Space Science and Technology program, drawing from a pool of nearly 1,000 applicants.

With this year’s fellows, the 91̽��continues its trend of consistently outcompeting other universities in its representation of fellows across all disciplines touched by NASA science, said , a 91̽��professor of civil and environmental engineering who has advised five fellows from previous years. In 2015, seven 91̽��graduate students won the fellowship, and according to records from 2007 forward, at least one 91̽��student has earned the fellowship nearly every year.

“The 91̽�� is unique in its success across all disciplines of NASA, its regular and continued performance across all years, and in what these students have gone on to do,” Lundquist said. “NASA fellows must have a unique combination of technical know-how as well as scientific understanding. This legacy highlights how 91̽��has been at the forefront of the technology and data-science revolution.”

NASA graduate fellowships provide funding for three years. Fellows at the 91̽��often go on to do research at NASA centers or become faculty members at major universities.

Several previous fellows have returned to the 91̽��as research scientists and professors, including (civil and environmental engineering) and (environmental and forest sciences). Shean and Kane are now serving as advisors for current NASA fellows at the UW.

“The NASA fellowship program provided the essential support, computing resources and training that I needed for my 91̽��Ph.D. research,” Shean said.��“I’m thrilled to see continued NASA support for top 91̽��students under this program, and excited about my new role training the next generation of NASA researchers.”

Here are this year’s fellowship winners and information about what they will study:

Benjamin Barr, atmospheric sciences

When ocean waves break in strong winds, they release showers of spray droplets into the air. These droplets transfer heat and moisture to the air, but the transfers are difficult to predict because the processes involved are complex. Barr will work with NASA to develop a model for predicting heat and moisture transfer to the atmosphere by spray, which will be incorporated into larger NASA models used to make predictions for weather and climate.

“The fellowship is a fantastic opportunity to work with NASA experts in many fields of study. It brings us into a broad community of researchers who will become our friends and colleagues during our career,” Barr said. “This exposure to researchers on the cutting edge of science is invaluable to young scientists who are developing their own research focuses.”

Shashank Bhushan, civil and environmental engineering

The mountain ranges surrounding the Tibetan Plateau have the largest concentration of glaciers outside of the polar regions. Each year, water melting from these glaciers replenishes the major river systems in the area and provides freshwater to millions of people living downstream. The glacier melt also contributes to global sea level rise.

Understanding how these glaciers behave has important implications for regional freshwater supply and sea level changes, Bhushan said. During his fellowship, Bhushan will use high-resolution satellite imagery to calculate glacier mass balance and movement patterns along the Tibetan Plateau and the surrounding region.

“I am always awestruck by the utility satellites offer in studying landform processes at remote locations, like how I can observe glaciers in High Mountain Asia from a desk in Seattle,” Bhushan said. “I am looking forward to interpreting these observations and tying them with established laws of glacier physics. In the longer term, this project will provide a foundation for my intended career as a glaciologist specializing in remote sensing.”

Lauren Satterfield, environmental and forest sciences

Large plant-eating mammals, such as deer and elk, can reduce the amount of flammable brush in the forest as the animals eat and trample plants. These activities can help reduce burnable fuels on a landscape, impacting where a wildfire starts and how it grows. But researchers still don’t know what effects the predators of deer and elk — including wolves and cougars — might have on this natural cycle.

Satterfield will combine NASA data on forest canopies with GPS collar data from both predators and their prey to understand the role these animals play in regulating the amount of fuel and severity of wildfire in areas across Washington and the Pacific Northwest.

“This NASA project will allow me to take my Ph.D. work, which focuses on understanding predator-predator and predator-prey interactions, and apply it in an exciting new direction with potentially widespread implications for how we manage for fire in the future,” Satterfield said. “Long-term, I seek to use ecology and predictive modeling to address issues of global climate change in ecosystems heavily influenced by people.”

The fellowship used to be called the and was renamed in 2019. More information on this year’s selection process is available .

These events are unpredictable and difficult to forecast. Yet they will become more common as the planet warms and more winter precipitation falls as rain rather than snow.

91̽�� mountain hydrology experts are using the physics behind these events to better predict the risks.

“One of the main misconceptions is that either the rain falls and washes the snow away, or that heat from the rain is melting the snow,” said , a 91̽��doctoral student in civil and environmental engineering. He will present his research Dec. 18 at the annual meeting of the .

Most of the largest floods on record in the western U.S. are associated with rain falling on snow. But it’s not that the rain is melting or washing away the snow.

Instead, it’s the warm, humid air surrounding the drops that is most to blame for the melting, Wayand said. Moisture in the air condenses on the cold snow just like water droplets form on a cold drink can. The energy released when the humid air condenses is absorbed by the snow. The other main reason is that rainstorms bring warmer air, and this air blows across the snow to melt its surface. His work support previous research showing that these processes provide 60 to 90 percent of the energy for melting.

Places that experience rain-on-snow flooding are cities on rivers that begin in the mountains, such as Sacramento, California, and Centralia, Washington. In the 1997 New Year’s Day in Northern California, melting snow exacerbated flooding, which broke levees and caused millions of dollars in damage. The biggest recent rain-on-snow event in Washington was the in the Snoqualmie basin. And the in summer of 2013 included snow from the Canadian Rockies that caused rivers to overflow their banks.

The 91̽��researchers developed a model by recreating the 10 worst rain-on-snow flooding events between 1980 and 2008 in three regions: the Snoqualmie basin in Washington state, the upper San Joaquin basin in central California and the East North Fork of the Feather River basin in southern California.

Their results allow them to gauge the risks for any basin and any incoming storm. The three factors that matter most, they found, are the shape of the basin, the elevation of the rain-to-snow transition before and during the storm, and the amount of tree cover. Basins most vulnerable to snowmelt are treeless basins with a lot of area within the rain-snow transition zone, where the precipitation can fall as snow and then rain.

Trees reduce the risk of flooding because they slow the storm’s winds.

“If you’ve ever been in a forest on a windy day, it’s a lot calmer,” Wayand said. That slows the energy transferred from condensation and from contact with warm air to the snowpack.

Simulations also show that meltwater accounted for up to about a quarter of the total flooding. That supports earlier research showing that snow is not the main contributor to rain-on-snow floods, but cannot be neglected since it adds water to an already heavy winter rainstorm.

The complexity of mountain weather also plays a role.

“The increase in precipitation with elevation is much greater than usual for some of these storms,” said , a 91̽��associate professor of civil and environmental engineering. “Higher flows can result from heavier rainfall rates at higher elevations, rather than from snowmelt.”

In related work, Lundquist’s group has developed a and is in the foothills east of Seattle. The scientists aim to better understand how changes in climate and forestry practices might affect municipal water supplies and flood risks.

Wayand and another student in the group have developed a high school for Seattle teachers to explain rain-on-snow events and the physics behind why they occur. They hope to begin teaching the curriculum sometime next year.

The other collaborator on the work being presented in San Francisco is at the National Center for Atmospheric Research in Colorado.

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For more information, contact Wayand at 360-265-7720 and nicway@uw.edu or Lundquist at 206-685-7594 and jdlund@uw.edu.

It’s a foggy fall morning, and 91̽�� researcher pokes her index finger into the damp soil beneath a canopy of second-growth conifers. The tree cover is dense here, and little light seeps in among the understory of the about 30 miles east of Seattle.

She digs a small hole in the leaf-litter soil, then pushes a thumb-sized device, called an iButton, about an inch beneath the surface. If all goes well, this tiny, battery-powered instrument will collect a temperature reading every hour for 11 months. Researchers hope this tool and a handful of other instruments will help them map winter temperatures throughout the watershed as they track snow accumulation and melt.

This fieldwork piggybacks on a recent finding by , a 91̽��associate professor of civil and environmental engineering, and her lab that shows that tree cover actually causes snow to melt more quickly on the western slopes of the Pacific Northwest’s Cascade Mountains and other warm, Mediterranean-type climates around the world. Alternatively, open, clear gaps in the forests tend to keep snow on the ground longer into the spring and summer. Lundquist and her colleagues published their online this fall in .

Common sense says that the shade of a tree will help retain snow, and snow exposed to sunlight in open areas will melt. This typically is the case in regions where winter temperatures are below freezing, such as the Northeast, Midwest and most of central and eastern Canada. But in Mediterranean climates – where the average winter temperatures usually are above 30 degrees Fahrenheit – a different phenomenon occurs. Snow tends to melt under the tree canopy and stay more intact in open meadows or gaps in a forest.

This happens in part because trees in warmer, maritime forests radiate heat in the form of long-wave radiation to a greater degree than the sky does. Heat radiating from the trees contributes to snow melting under the canopy first.

“Trees melt our snow, but it lasts longer if you open up some gaps in the forest,” Lundquist said. “The hope is that this paper gives us more of a global framework for how we manage our forests to conserve snowpack.”

For the study, Lundquist examined relevant published research the world over that listed paired snow measurements in neighboring forested and open areas; then she plotted those locations and noted their average winter temperatures. Places with similar winter climates – parts of the Swiss Alps, western Oregon and Washington, and the Sierra Nevada range in California – all had similar outcomes: Snow lasted longer in open areas.

“It’s remarkable that, given all the disparities in these studies, it did sort out by climate,” Lundquist said.

Even in the rainy Pacific Northwest, we depend on yearly snowpack for drinking water and healthy river flows for fish, said Rolf Gersonde, who designs and implements forest restoration projects in the Cedar River Watershed. Reservoirs in the western Cascades hold approximately a year’s supply of water. That means when our snowpack is gone – usually by the summer solstice – our water supply depends on often meager summer rainfall to get us through until fall, he said. Snowpack is a key component of the Northwest’s reservoir storage system, so watershed managers care about how forest changes due to management decisions or natural disturbances may impact that melting timetable.

The UW’s research in the watershed has been a beneficial partnership, researchers say. The 90,000-acre watershed is owned by the City of Seattle and provides drinking water to 1.4 million people. The area now is closed to recreation and commercial logging, but more than 80 percent of the land was logged during the early 20^th century, and a large swath of dense, second-growth trees grows there now. Watershed managers have tried thinning and cutting gaps in parts of the forest to encourage more tree and plant diversity – that then leads to more diverse animal habitat – offering the 91̽��a variety of sites to monitor.

The 91̽��researchers acknowledge that temperature is a very broad predictor of snowmelt behavior, yet they expect their theory to hold true as they look more closely at the relationship between climate and snowmelt throughout the Pacific Northwest. They are collaborating with researchers at Oregon State University and the University of Idaho, and are ramping up a citizen science project asking hikers and snowshoers to .

“This is really just a start,” said Dickerson-Lange, a doctoral student in Lundquist’s lab who is coordinating the citizen-science observations. “The plan is to refine this model. With climate change, a cold forest now might behave more like a warm forest 100 years from now. We want to be able to plan ahead.”

Co-authors of the recent paper are of 91̽��civil and environmental engineering and of Utah State University.

Funding for the research is from the National Science Foundation.

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For more information, contact Lundquist at jdlund@uw.edu or 303-497-8257 and Dickerson-Lange at dickers@uw.edu or 253-225-9909. Lundquist is on sabbatical but is reachable by email or phone.