Variability and trends in Mountain Snowpack in Western North America

Snow course and SNOTEL measurements of spring snowpack, corroborated by a physically-based hydrologic model, are examined here for climate-driven fluctuations and trends during the period 1916-2002. Much of the mountain West has experienced declines in spring snowpack, especially since mid-century, and despite increases in winter precipitation in many places. Analysis and modeling shows that climatic trends are the dominant factor, not changes in land use, forest canopy, or other factors. The largest decreases have occurred where winter temperatures are mild, especially in the Cascade Mountains and Northern California. In most mountain ranges, relative declines grow from minimal at ridgetop to substantial at snowline. Taken together, these results emphasize that although the Pacific Decadal Oscillation has played some role in fluctuations in the region’s SWE, the West’s snow resources are already declining as Earth’s climate warms.