Scientists project earlier spring snowmelt in Washington State

Using models that include both climate and surface hydrology, scientists have created simulations of future April 1 snowpack in Washington State. The simulations project that by the 2020s, there will be 27-29% less snow on the ground on April 1 than the long-term historical average.  By the 2040s, the projected reduction is 37-44%, and by the 2080s, 53-65%.[[Elsner, Marketa M. et. al. “Implications of 21st Century Climate Change for the Hydrolody of Washington State.” (PDF) The Washington Climate Change Impacts Assessment: Evaluating Washington’s Future in a Changing Climate (2009): 69-106.]] These reductions are a consequence of the higher average temperatures projected by climate models for the Pacific Northwest — roughly 1.5 to 7 degrees F by 2050, and 3 to nearly 10 degrees F by 2100, depending importantly on the amount of greenhouse gases added to the atmosphere over the century.[[Mote, Phillip W., and Eric P. Salathe Jr. “Future Climate in the Pacific Northwest.” (PDF) The Washington Climate Change Impacts Assessment: Evaluating Washington’s Future in a Changing Climate (2009): 21-43.]]

The analysis also shows a median projection of a few percent increase in precipitation by 2100, with a large range of uncertainty that spans roughly a 15% decrease to an increase of nearly 30%.

An independent analysis recently estimated that even without any changes in precipitation, snowpack in the Cascades should decrease by 20% per 1.8 degrees F of warming.[[Casola, Joseph H., et. al. “Assessing the Impacts of Global Warming on Snowpack in the Washington Cascades.” (Abstract) Journal of Climate 22, no. 10 (May 2009): 2758-2772.]]

These trends continue and amplify the earlier average snowmelt that is already taking place across the American West.[[Stewart, I. T., D. R. Cayan, and M. D. Dettinger. “Changes in snowmelt runoff timing in western North America under a ‘business as usual' climate change scenario.” (PDF) Climatic Change 62, no. 1 (2004): 217-232. PDF]]