Water securityWater resources in Western U.S. threatened by declining snow mass

Researchers have now mapped exactly where in the Western U.S. snow mass has declined since 1982.

A University of Arizona-led research team mapped the changes in snow mass from 1982 to 2016 onto a grid of squares 2.5-miles on a side over the entire contiguous U.S.

A person could practically find the trend for their neighborhood, said first author Xubin Zeng, a UA professor of hydrology and atmospheric sciences. Grid size for previous studies was about 40 miles on a side, he said.

“This is the first time anyone has assessed the trend over the U.S. at the 2.5-mile by 2.5-mile pixel level over the 35-year period from 1982 to 2016,” Zeng said.  “The annual maximum snow mass over the Western U.S. is decreasing.”

In the Eastern U.S., the researchers found very little decrease in snow mass.

Even in snowy regions of the West, most of the squares did not have a significant decrease in snow. However, some parts of the Western U.S. have had a 41 percent reduction in the yearly maximum mass of snow since 1982.

UA co-author Patrick Broxton said, “The big decreases are more often in the mountainous areas that are important for water supplies in the West.”

Snow mass is how much water it contains, which is important in regions where winter snows and subsequent snow melt contribute substantially to water resources. Snow melt contributes to groundwater and to surface water sources such as the Colorado River.  

Snow is also important for winter sports and the associated tourism, which is a multi-billion-dollar industry in the U.S.

If all the squares in the Western U.S. that had a 41 percent reduction in snow mass were added up, the combined area would be equal in size to South Carolina, said Zeng, who holds the Agnese N. Haury Chair in Environment. He and his team looked at the interannual and multidecadal changes in snow mass for the contiguous U.S.