Seasonal snowpack covers 46 million square kilometers annually—31% of Earth’s land area—but that number is shrinking. Snowpack is accumulating later, melting earlier, and retreating at an even faster rate than Arctic sea ice. This reduction in snowpack has implications for water locally and climate globally.
“Snow is an enormous regulator of heat on Earth because of its high reflectivity,” said Matthew Sturm, group leader of the Snow, Ice and Permafrost Group at the University of Alaska Fairbanks Geophysical Institute. “The Earth gets rid of enormous amounts of heat by painting itself white in the winter, and that’s going away.”
Just how substantial will changes brought by shrinking snowpack be? SnowEx, a multiyear NASA research program, hopes to find out. SnowEx has tested sensors in Western states since 2017; this winter the research continues in Alaska, a state with applicable infrastructure, experience, and plenty of snow.
A Satellite for Snow
Every 10 years, an independent panel assesses NASA’s satellite fleet and recommends research areas that are currently unmet. The 2017 decadal survey suggested snow (and, specifically, snow water equivalent) as a possible mission focus for NASA’s Explorer program.
“[Snow water equivalent] is a critical component of hydrologic cycling and the Earth’s energy balance, but it’s really difficult to measure,” said Carrie Vuyovich, project scientist for SnowEx Alaska and a research physical scientist at NASA’s Goddard Space Flight Center. Field observations provide valuable data, but only in limited areas. “It means a huge amount of landscape is missing information,” she said. “Satellites are really the ideal observers to cover that amount of area.”
To prepare for a potential satellite mission, SnowEx scientists are developing and refining aircraft-mounted sensors adaptable across a range of conditions. There’s no guarantee of a satellite launch—“It’s a competitive process,” said Vuyovich—but the snow science community can prepare for the potential opportunity by testing sensors calibrated to the temporal and spatial intricacies of snow.
Tundra Crust and Taiga Woods
A snow-focused satellite should work in all regions, from deep mountain powder to dense tundra crust. Sensors must also react to complicated conditions: wet snow, deep snow, snow covered by trees. SnowEx’s mobility allows it to refine algorithms and accuracy in various conditions, and Alaska is essential for testing those abilities.
“The large fraction of global snowpack is here at higher latitudes,” said Svetlana Stuefer, an associate professor of civil and environmental engineering at the University of Alaska Fairbanks. As deputy project scientist for SnowEx Alaska, Stuefer is helping coordinate the campaign and identifying locations that represent the world’s two largest snow biomes: Arctic tundra and boreal forest, also called taiga.
“Tundra and taiga take up a lot of room, but they pose two different problems,” said Sturm, a senior adviser to SnowEx Alaska.
Tundra snow is shallow, stratified, and often located on permafrost. Remote sensors must recognize and respond to those conditions. Taiga is more complex. “Sorting out what’s on the ground and what’s on the trees is very difficult,” said Sturm. Snow suspended from tree branches reflects light (which is good for climate control) but may sublimate into the atmosphere without contributing to groundwater. A snow-focused satellite would need sensors attuned to both climate and water issues.
“I’m excited to see where [SnowEx] goes. They have a lot of challenges ahead of them, but I think it can be an important tool,” said Daniel Fisher, a senior hydrologist with the U.S. Department of Agriculture’s Alaska Snow Survey not involved in the project. “I don’t think [remote sensing] will ever be a silver bullet, but I do think it will play an important role in understanding and measuring the snowpack across the state,” he said.
Fixing the Data Drought
SnowEx scientists plan to fly lidar and stereophotogrammetry sensors in Alaska this winter. Another aircraft will carry the Snow Water Equivalent Synthetic Aperture Radar and Radiometer (SWESARR), a specialty SnowEx instrument developed at Goddard to calculate snow water equivalent (SWE) using active and passive microwaves. Field staff will measure snow conditions on the ground to compare observations.
Better snow data could benefit a range of interests, from road crews to flood forecasters to subsistence trappers. Increased SWE data would particularly help water managers; one in six people relies on seasonal snowpack for drinking water.
Then there are the recreationalists, like backcountry skiers who scan avalanche reports while brewing their morning coffee.
“Right now, operationally, we are extremely reliant on point-based observations,” said Andrew Schauer, a lead forecaster for the Chugach National Forest Avalanche Information Center not involved in SnowEx. Avalanche centers are challenged by a lack of data, he said, but aerial observations could fill that gap if updated quickly. “I’m excited to see what becomes of the SnowEx program,” he said.
By preparing sensors for all winter conditions, SnowEx scientists hope to be ready should NASA ask for a mission proposal. Research in Alaska is an important step to reaching that goal.
“[SnowEx Alaska] positions us to be competitive,” said Sturm. “I don’t think there’s any question that a satellite for snow would help humanity.”
—J. Besl (@J_Besl), Science Writer