Western snowpack could plummet this century

The snow-capped mountains of the American West are more than just picturesque: Ecosystems as well as farms and towns across the region depend on snowpack accumulation for their water supply. But over the next few decades, much of the snow falling on lower-elevation peaks is going to be replaced with rain, according to new projections for the western U.S., which could throw water planning way off balance.

A University of Idaho team studied the rain-snow transition zone — a place where a mostly rainy region bumps up against a snow-dominated one. The transition zone naturally moves up and down a mountain with the passing of the seasons, but the team wanted to see if climate change was affecting the position of this zone, and thus the extent of winter snowfall. The researchers combined historic observations with climate modeling of future temperatures and precipitation to map out the rain-snow transition zone across the West for the late 1970s through the middle of this century.

Their projections indicate an average 30 percent decrease in the extent of land area with temperatures conducive to snowfall by the mid-21st century. And the length of the snowy season across the mountainous regions will be cut short by roughly two months. Instead of November through March, expect fresh powder from Thanksgiving through Valentines’ Day, with a mix of rain and snow to bookend those months. The effect will be severest on shorter, mid-elevation ranges such as the Northern Rockies, North Cascades, and Blue Mountains.

Parts of the Southwest saw near-record lows in snowfall this year. These new predictions of more rain but less snow during the winter could add to western water woes: Instead of a steady water supply driven by snowmelt in warmer months, rainwater rushing downstream would produce summer droughts and winter floods. — Janet Fang | 26 June 2014

Source: Klos, P.Z., Link, T.E. & Abatzoglou, J.T. Extent of the rain-snow transition zone in the western U.S. under historic and projected climate, Geophysical Research Letters (2014). doi:10.1002/2014GL060500

Image: bl0ndie | shutterstock.com