Snow course data Collected primarily ~April 1 beginning in 1915 (most in 1940s), added other months Purpose: streamflow forecasting Administered by USDA Natural Resource Conservation Service Mostly discontinued, some replaced by SNOTEL
Changes in SWE vs changes in precip 1930s to 1990s1945-55 to 1990s Obs SWEVIC SWEPrecipObs SWEVIC SWEPrecip Cascades-14%+1%+4%-29%-16%-5% Rockies+11%+2%+9%-16%-9%+1% California+3%-14%+10%-2%-25%-1% Interior+9%-6%+10%-22%-18%+2%
Trends/15yr in snow days in Switzerland From Scherrer et al., GRL 2004
Trends in Swiss snow days attributed to temperature and precipitation precip and temp attributions; contour lines indicate the sum. Attribution of trends shown by pseudo vectors; altitude and latitude From Scherrer et al., GRL 2004 days/42 yrs.
Conclusions Observations show substantial declines in western snowpack; corroboration with VIC suggests they are real and largely temperature-driven Cascades, N. Calif most temp-sensitive Large increases in precipitation have offset warming in some places Is global warming causing the decline? Too soon to tell.