The Importance of Snowpack

by Mike Kolian

In the United States, changes in snowpack currently represent one of the best documented hydrological signs of climate change. Snowpack is a key indicator and plays a vitally important role both in the environment and to society.

Snowpack accounts for a majority of water supply in many parts of the West as it stores vast amounts of water that is slowly released as temperatures rise in the spring and summer. Snowpack keeps the ground and soil moist by covering it longer into spring and summer which influences the onset of the fire season as well as the prevalence and severity of wildfires. In addition, hydro-electric power generation in the West is heavily reliant on water supplied by melting snowpack.

A very serious story is unfolding out West. This year, snowpack in the western U.S. is at record lows in the Sierra Nevada and Cascades of California, Oregon, and Washington, confirmed by the recent April 1st snowpack measurements. In fact, some snowpack sites in California and Washington were observed to be snow-free this spring for the first time since observations began.

Snowpack is measured in snow-water equivalent, which reflects the amount of water contained in the snowpack at a location (if the entire snowpack were to melt). This indicator is based on data from over 700 measurements sites across 11 western states and shows long-term rates of change for the month of April, which could reflect changes in winter snowfall as well as the timing of spring snowmelt.

map chart titled "Trends in April Snowpack in the Western United States 1955-2015." Charts shows mostly percentage reductions of snowpack over all mountains areas, ranging from 0 to -80 percent. Very few areas show small increases.

Over the last 60 years, there have been widespread temperature-related reductions in snowpack in the West, with the largest reductions occurring in lower elevation mountains in the Northwest and California. From 1955 to 2015, April snowpack declined at over 90 percent of the sites measured (see map). The average change across all sites amounts to about a 14 percent decline. Observations also indicate a decrease in total snowfall and a transition to more rain and less snow in both the West and Northeast in the last 50 years.

photo of a resevoir with water levels dropped way below usual level

Long-term trends in snowpack provide important evidence that climate-related shifts are underway, and highlight the seriousness of water-resource and drought issues that Western states such as California currently face.

Less snowpack means less water and less water means more serious impacts.

Explore more:

See this and other Snow and Ice indicators

Open the map in Google Earth (KMZ) (100K, Download Google Earth): http://www.epa.gov/climatechange/images/indicator_downloads/snowpack_april1.kmz

About the author: Mike Kolian is an environmental scientist with EPA’s Office of Atmospheric Programs, Climate Change Division. His deep roots managing long-term environmental monitoring programs form the basis of his appreciation for the important role they and their data play in scientifically based decision making.

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