Snowpack in the Western US is a critical component of the annual water supply. Most precipitation in this region falls in the cold season and is temporarily stored as mountain snow, which melts in spring to recharge reservoirs which hold water for human consumption through the remainder of the year, including the high-demand summer months when very little precipitation falls.
Snowpack has shown a steady decline in the last 50 years, which is a source of considerable concern for the region's water managers (Service, 2004). Peak snowmelt in much of the region is 5 to more than 20 days earlier than 50 years ago, and large areas have spring snowpack reduced more than 60% over this time period.
Consequences of this change in timing of snowmelt are significant for western agriculture, much of which depends on irrigation. Forests are more exposed to drying conditions, which start earlier due to earlier snow loss. Declining stream flows will negatively impact riparian ecosystems and fish populations. Excessive streamflow due to more rapid snowmelt might also lead to more springtime flooding.
Building of large new dams, widely considered inadvisable due to environmental impacts, is being reconsidered to cope with expected continuation of these trends.
Reference
Service, R.S., 2004: As the West goes dry. Science, 303, 1124-1127.