Patrick Broxton, right, a member of Xubin Zeng’s team, measures snow mass.

Even in the desert, or maybe especially in the desert, snowpack is important. Melting snow from the Rocky Mountains and Sierra Nevada replenishes surface watersheds and underground aquifers.

In addition, says Xubin Zeng, professor of hydrology and atmospheric sciences, snowpack in both the eastern and western United States can also help with weather forecasting and climate projections and provide clues about the effect of global warming.

Zeng’s team uses new ideas to compile data from citizen volunteers who measure snow depth at one specific point and from networks that measure both snow depth and snow mass operated by government agencies.

The resulting snowpack dataset is available from October 1981, and data quality is ensured by passing four rigorous tests.

Zeng says his group’s work disputes previous claims of a “statistically significant” decrease in the maximum snow mass in the western U.S. His data shows that only 13 percent of the 2.5-mile-by-2.5 mile snowy pixels show significant trends over that area.

Zeng’s work also shows the reasons for snowpack changes and trends. It’s not just the warming of the globe, but the effects of precipitation in the West. In the eastern part of the country, it’s primarily temperature.

“In the eastern U.S., snowpack change is directly linked to warming. Over the western U.S., you need to consider both temperature and precipitation changes.

“You cannot just talk about global warming or temperature change,” he says.

The work Zeng’s team is doing is being used by NASA’s Jet Propulsion Laboratory in Pasadena, California, to test various technologies for future satellite measurements of snow mass and depth.

“That’s the best endorsement,” he says.