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Science

Scientists Prepare The West For Drought By Measuring Water Contained In Snowpack

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Dan McGrath
Members of the CSU team, Ella Bump (left) and Lucas Zeller (right), work at one of their research sites on Cameron Pass.

As Colorado enters the hottest months of the year, drought and high temperatures are on most people's minds. But researchers at Colorado State University are still focused on snow.

For the past few winters, CSU professor Dan McGrath and his graduate students have made a bi-weekly trek up Cameron Pass. When they arrive, they split into various tasks designed to measure the snowpack.

Some of the team will strap on snowshoes and start pulling a large sled. The sled holds a ground-penetrating radar system.

“The radar instrument transmits a pulse of radio energy,” said McGrath. “And we basically measure the time it takes to travel from the instrument down to the ground-snow interface and then back up to the instrument.”

Throughout the season, the researchers see longer and longer delays in the radar travel time as the snowpack builds up. It’s just the opposite when the snow begins to melt.

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Dan McGrath
Graduate student Randall Bonnell drags the sled holding the ground-penetrating radar.

In addition to the radar measurements, graduate student Alex Olsen-Mikitowicz flies a drone in a grid. It takes images that he uses to construct a 3D model of the area.

“It’s basically like taking your field site home with you. We can fly around in this model just kind of like a video game,” said Olsen-Mikitowicz. “So we have these every time we go out, and we can then stack them up on top of each other and basically watch the snow accumulate and melt over time.”

Meanwhile, graduate student Ella Bump digs a snow pit about a meter deep. The team takes measurements of snow temperature and density every 10 centimeters or so. Bump uses a metal tool shaped like a slice of cake to cut out chunks of snow.

“This is a wedge cutter for measuring density, and it's got a volume of one liter,” she said. “And so, when we take density measurements, we just weigh this and then we can figure out the density from there.”

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Dan McGrath
Ella Bump digs a snow pit so the team can take measurements of each layer in the snowpack.

All of these tasks have the same end goal, according to Dan McGrath — measuring the snow-water equivalent, or how much total water is stored in the snowpack.

“At present there’s no single way of doing that,” he said. “And that’s why this NASA campaign is occurring, is to test and evaluate these different approaches.”

The CSU research group is one of many across the West working together on NASA’s SnowEx campaign. U.S. Forest Service hydrologist and SnowEx scientist Kelly Elder said the project came together because the nationwide team wanted to measure snow with a satellite in space.

“The fantasy was that we could just shoot pictures in some area of the spectrum of Earth’s surface with snow on it and get answers, he said. “After decades of frustration, we’ve figured out that we really need two other elements to pull it all together.”

The other two necessities are on-site measurements, like the ones on Cameron Pass, and computer models. Without them, images from current satellites can only measure how much area is covered by snow — not how much water is actually in the snow.

That’s because of the snow’s internal properties. One of the main problems is the amount of liquid water in the snowpack. Radar systems send waves of energy through the snow that move at a certain speed depending on the material. Just like a person would move slower running in water than on land, the waves move slower in water than in snow. Without measurements of the amount of liquid water within the snowpack, it’s difficult to tell if the layer of snow is thick or simply wet.

However, the amount of water in snow is what’s important for water managers because 70 to 80 percent of the water for Western cities and agriculture comes from snowpack.

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Dan McGrath
Graduate student Lucas Zeller takes and records measurements in one of the burned areas near Cameron Peak. This season, McGrath said the snow in burned areas melted faster than in unburned areas.

“Even over a basin the size of the Poudre, we have relatively high uncertainty in our predictions of how much water is going to come out on any given year, even with a long record,” said Elder. “If you throw climate change in on top of that, we’ve got a real problem.”

Current predictions of snow-water equivalent come from observations of water levels in previous years. Elder said that as global warming changes the environment, that process becomes invalid.

Future satellites, combined with the work on the ground, might address the problem. NASA and the Indian Space Research Organization have partnered to launch one at the beginning of 2023.

But that satellite isn’t specifically made to measure snow — it’s just a bonus. While the data will be useful, McGrath said a perfect solution is probably still years away.

“The goal of this whole campaign is to be able to measure this snow-water equivalent from space and do it globally all the time, essentially. So, every 10 days or 12 days, we’d have this image of how much snow is on the ground in these locations,” he said. “That will just hugely inform how agriculture is done and how water is managed, especially in a changing climate.”

The CSU team plans to keep working on different tools to measure snow-water equivalent. Next summer, they’re headed to Alaska to conduct measurements in an environment with different conditions.

Although measuring the amount of water in snow may not solve the drought problem, McGrath said it will make the West more prepared.

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