Abstract

In western North America, most of the annual precipitation falls during the cool half of the year and is stored as snowpack in the mountains. Springtime warming melts this snow starting at low elevations, and the melt continues through the summer at some of the coldest locations. Such meltwater provides the majority of water resources during the region’s dry summers, watering millions of acres of farmland and providing other economic, environmental, and recreational benefits.

Snow is thus a key aspect of the region’s economy. Evidence is mounting that winter and spring temperature have increased in western North America. Such evidence includes direct meteorological observations (Folland et al., 2001), declines in snow cover (Groisman et al., 1994), earlier spring melt peak in most streams (Cayan et al. 2001) and earlier occurrence of key phonological indicators in several species (Cayan et al. 2001). Recently, a study of springtime mountain snowpack in the Pacific Northwest (Mote, 2003) showed widespread declines in snowpack since 1950 at most locations with largest declines at lower elevations indicating temperature effects.

This study expands the geographic scope of the earlier study to encompass all snow courses in the western U.S. and British Columbia.