Abstract

Arid and semi-arid regions of the intermountain west (eastern Sierras to southern Rockies) that receive little summer precipitation are dependent on winter snow to satisfy downstream human and ecological water needs. Although decreases in snowpack depth and earlier snowmelt have been widely documented in the Western U.S. over the last 50 years, snowpack trends in the intermountain west are less apparent due to higher elevations and colder conditions. The goal of this study was to investigate the spatial variability of snowpack depth and snowmelt timing across the intermountain west by evaluating 30 years of SNOTEL records at three scales: 202 individual SNOTEL stations, 29 sub-basins, and 13 larger basins. Trends in maximum snow water equivalent (SWE) were only significant at 7 stations (6 of 7 were declining), 112 had negative slopes (>5mm/year), 24 has no slope, and 64 has positive slopes (>5mm/year). Despite a lack of significant trends at the individual stations, Regional Kendall analyses showed statistically significant decreasing maximum SWE and earlier melt in 6 of the 13 larger basins, with greater SWE declines in higher elevation basins. The maximum SWE declined 2 to 5 mm/year in both southern and northern tributaries to the Colorado River with mean elevations above 2500 m. The lack of widespread elevation or latitudinal controls is partially explained by variable winter lapse rates among the basins and sub-basins. The results suggest that snowpack conditions in the intermountain west could vary significantly during periods of intense warming (such as the last 15 years). This work therefore provides both an empirical understanding of recent snowpack conditions and context for how long-term temperature increases from climate change could influence snowpack in the major river basins of the intermountain west.

Citation

Harpold, A.A., Rajagopal, S., Heidbuechel, I., Stielstra, C., Jardine, A.B., Brooks, P.D. (2010): Trends in Snowpack Depths and the Timing of Snowmelt in the River Basins of the Intermountain West . AGU Fall Meeting Abstract H31I-08..