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Fifth National Climate Assessment - Read the Report

Monitoring snowpack change


Trends in April snowpack in the western United States, 1955–2020, measured in terms of snow water equivalent from ground-based stations. Large and consistent declines in April snowpack have been observed over this time period, with an average decline of about 19 percent at the sites measured. Blue circles represent increased snowpack; red circles represent a decrease. Source: EPA, using data from the USDA Natural Resources Conservation Service.

A multiyear observing campaign is tracking changing snowpack in the western United States, laying the groundwork for a future snow satellite mission.

Snowpack plays a critical role in the water cycle and helps regulate Earth’s climate. Storage of snow in the winter feeds spring snowmelt, bringing water to crops, people, and ecosystems downstream. Snowpack also feeds hydropower generation in  the Southwest and Northwest, and snow-related tourism and recreation are important economic drivers in many regions.1 Warmer winter temperatures and other climate-related changes are altering the timing, accumulation, and melt of snow. Large declines in snowpack in the western United States and shifts to more precipitation falling as rain rather than snow in many parts of the central and eastern United States are expected as the climate continues to warm,2 and decision-makers need accurate snow information to respond to changing snow and water availability.

Remote sensing technologies allow scientists to monitor how snow cover is changing over time, but many aspects of snow cover are still difficult to measure. The SnowEx campaign is a multiyear effort to address key gaps in snow remote sensing  knowledge, focusing on airborne campaigns and fieldwork in North America. Coordinated studies are underway to help determine which combination of instruments and techniques can deliver the needed information for researchers and decision-makers, and lay the groundwork for a future snow satellite mission.

SnowEx is led by NASA, with participation from NOAA, DoD, and the USDA Forest Service. In 2020, the U.S. Army Corps of Engineers, Engineer Research and Development Center-Cold Regions Research and Engineering Laboratory (ERDC-CRREL) deployed novel ground-based, mobile, and airborne sensing platforms to investigate the season’s evolving snowpack in the western United States. Other coordinated airborne and field-based experiments tested instruments under a variety of snow conditions, including the ability to measure snow water equivalent (the amount of water held in a volume of snow), a critical indicator for water resources. This will augment the ground-based measurements of snowpack, such as from the snow telemetry (SNOTEL) network and other measurement stations (see figure).

These coordinated observations showed how changes in snowpack impact water management, water security, and hazard assessments in a changing climate, and will inform the design of a future snow satellite mission.


1Jay, A., D.R. Reidmiller, C.W. Avery, D. Barrie, B.J. DeAngelo, A. Dave, M. Dzaugis, M. Kolian, K.L.M. Lewis, K. Reeves, and D. Winner, 2018: Overview. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 33–71. https://doi.org/10.7930/NCA4.2018.CH1

2 Hayhoe, K., D.J. Wuebbles, D.R. Easterling, D.W. Fahey, S. Doherty, J. Kossin, W. Sweet, R. Vose, and M. Wehner, 2018: Our Changing Climate. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 72–144. https://doi.org/10.7930/NCA4.2018.CH2