Snowpack Variability and Trends across the San Juan Mountains of Southwestern Colorado from Snow Telemetry and Snowcourse Stations

Abstract:

The world’s mountains provide a crucial water source for one-sixth of the world’s population and in the Western United States (U.S.) 70– 80% of the annual discharge originates from snowmelt in the mountain watershed. Mountain snowpacks are recognized as a sensitive bellwether of global and regional change. The United States Department of Agriculture (USDA) has been collecting snow data across the Western United States at manual (snowcourse) stations since the 1930s and at automated (snow telemetry) stations since the 1970s. These USDA data have been used to investigate change across the Western U.S., and many stations have seen significant decreases in their snowpack.

Daily data from 34 SNOTEL stations and monthly data from 25 snowcourse stations across the San Juan Mountains of southwestern Colorado were used to evaluate the variability and trends in snow water equivalent (SWE) for the selected periods to assess if there has been a systematic change in the San Juan snowpack. April 1st and peak SWE decreased at almost all of the stations, with a significant decrease being observed at about half of the stations. Decreases were over the entire period of record, with large declines in the 1980s through the year 2000, but there tended to be no decrease in the past 15 years (2001 to 2015). On average the snow accumulation has been less in recent years (2001 to 2015) than over previous periods; at stations with a deeper snowpack these decreases have been much greater and illustrate a possible shift in winter climate occurring in the early 2000s.

The Center for Snow and Avalanche Studies (CSAS) in Silverton Colorado has been collecting comprehensive higher elevation meteorological and snowpack data since this possible climatic shift occurred. If the current snowpack regime represents a new normal, then existing and new data collected by CSAS will assist in interpreting changes within this regime.