Dramatic declines in snowpack in the western US

• Published in: NPJ climate and atmospheric science 2018-03, Vol.1 (1), Article 2
• Main Authors: Mote, Philip W., Li, Sihan, Lettenmaier, Dennis P., Xiao, Mu, Engel, Ruth
• Format: Article
• Language: English
• Subjects: 704/106/125; 704/242; Agricultural management; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Climate; Climate change; Climate Change/Climate Change Impacts; Climatology; Earth and Environmental Science; Earth Sciences; Global warming; Hydrologic cycle; Hydrologic models; Hydrology; Industrial applications; Lakes; Mountains; Rainy season; Researchers; Reservoirs; Runoff; Snow; Snow accumulation; Snow-water equivalent; Snowpack; Spring; Spring (season); Trends; Weather; Winter
• ISSN: 2397-3722; 2397-3722
• DOI: 10.1038/s41612-018-0012-1

Mountain snowpack stores a significant quantity of water in the western US, accumulating during the wet season and melting during the dry summers and supplying much of the water used for irrigated agriculture, and municipal and industrial uses. Updating our earlier work published in 2005, we find that with 14 additional years of data, over 90% of snow monitoring sites with long records across the western US now show declines, of which 33% are significant (vs. 5% expected by chance) and 2% are significant and positive (vs. 5% expected by chance). Declining trends are observed across all months, states, and climates, but are largest in spring, in the Pacific states, and in locations with mild winter climate. We corroborate and extend these observations using a gridded hydrology model, which also allows a robust estimate of total western snowpack and its decline. We find a large increase in the fraction of locations that posted decreasing trends, and averaged across the western US, the decline in average April 1 snow water equivalent since mid-century is roughly 15–30% or 25–50 km 3 , comparable in volume to the West’s largest man-made reservoir, Lake Mead. Dramatic declines in snowpack in the western US Mountain snowpack stores huge amounts of water in the western US, supplying much of the water used to grow crops. A team of researchers from Oregon State University and UCLA found that spring snowpack declined almost everywhere, especially in the coastal states and other locations with mild winter climate. (Skiers will be relieved that declines were smaller in winter.) Not surprisingly, the declines are mostly related to warming climate. Using a physically-based model of the hydrologic cycle, which takes daily weather as inputs and computes snow accumulation and melt, runoff, etc., the researchers computed the total snowpack in the western US. Total snowpack declined 15–30%, and the amount of that lost water is comparable in volume to the West’s largest man-made reservoir, Lake Mead. Many water managers are already planning for a future with less snow, but this research emphasizes that the future is here.