Declining Mountain Snowpack in Western North America*

The West’s snow resources are already declining as the climate warms. Mountain snowpack in western North America is a key component of the hydrologic cycle, storing water from the winter (when most precipitation falls) and releasing it in spring and early summer, when economic, environmental, and recreational demands for water throughout the West are frequently greatest. In most river basins of the West, especially in Washington, Oregon, and California, snow (rather than man-made reservoirs) is the largest component of water storage; hence, the West is (to varying degrees) vulnerable to climatic variations and changes that influence spring snowpack.