Last updated October 15, 2021
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Western US Snow Drought Winter 2018

United States

Snow melt provides a sustained source of water for over one billion people globally and is a critically important resource in the western US and in California where the Sierra Nevada snowpack supplies one-third of the state's water supply.[1] In recent years, snow water equivalent (SWE)—the amount of water stored in the snowpack—in the western US has significantly diminished.[2]

Long-term climate warming is strongly correlated with declining snow water equivalent. And shifts in stream flow throughout the American West have been driven by decreased spring accumulation and/or increased spring melt.[3] The fingerprint of warming temperatures has been found in these trends at both broad scale[4][5][6][7] and in California in particular.[8][4][9][10]

SWE is measured on approximately the first of each month in the mountains of the western US during the winter season and reaches its basin-wide maximum on approximately April. These measurements indicate the condition of water resources. By February 2018, water resources in several states were a fraction of the historical average.

Many western states including California, Utah, Oregon, Washington, and Colorado are in the midst of a warm, dry winter.[11] In January, almost all of the open resorts in New Mexico, Arizona, Colorado, Utah, Nevada, and California were relying on man-made snow to operate.[11] These states have also experienced worsening drought in recent months.[12]

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Photo: Denver Post via Getty Images
Greenhouse Gas Emissions
Global Warming
Land Surface Temperature Increase
Air Mass Temperature Increase
Large Scale Global Circulation Change
Snowpack Melting Earlier and/or Faster
Precipitation Falls as Rain Instead of Snow
Atmospheric Blocking Increase
Snowpack Decline
Southwestern US Precipitation Decrease
Extreme Heat and Heat Waves
Drought Risk Increase
Western US Snow Drought Winter 2018