@ClimateCentral: Western Water Crunch Has Climate Change Fingerprints, Scientists Find

SNOTEL Site via the Natural Resources Conservation Service

From Climate Central (Bob Berwyn):

The American West has already lost between 10 and 20 percent of its mountain snowpack since the early 1980s, and climate change is partly to blame, new research shows. If greenhouse gas emissions are not curtailed, the region could lose 30 percent of the snowpack the region relies on for irrigation and drinking water—and potentially as much as 60 percent—over the next 30 years, the authors write.

The loss can’t be explained by natural climate variations alone, however it is consistent with model simulations that include both natural and human-caused changes, the study says.

“These results add to the evidence of a human influence on climate that will have severe impacts on our water supply,” said Benjamin Santer, a Lawrence Livermore National Laboratory climate scientist and a co-author of the paper, published last week in Nature Communications.

Less snowpack is more than just a blow to the skiing and snowboarding industries. The snow that falls in winter, and melts slowly during spring and summer, fills regional reservoirs and is used for irrigation, hydropower and drinking water. The Western snowpack, spread across thousands of miles of high-elevation terrain, holds far more water than all the reservoirs in the region combined.

“A 60 percent loss would be a huge concern to farmers, ranchers and water managers,” said lead author John Fyfe, a senior research scientist with Environment Canada, who did some of the earliest studies on global warming impacts to western water supplies.

The findings are based on data collected between 1982 and 2016 from 354 snow measuring stations across 11 states, from the Cascades of Washington and Oregon through California’s Sierra Nevada and the Rocky Mountains in Idaho, Wyoming, Montana, Colorado and New Mexico. The stations measure the amount of water in the snow, a critical metric for calculating downstream water supplies.

The maximum amount of water in the snowpack declined at 307 (87 percent) of the sites between 1982 and 2016 at a rate of about 9.5 percent per decade. Projecting ahead, the models show a range of potential losses over the next 30 years reaching as high as 60 percent under a high-emissions scenario but likely closer to 30 percent, the authors write.

Fyfe said the models his team used to project the snowpack decline are similar to those used for attributing the man-made global warming to single climate events like heatwaves or droughts. The models reproduce many possible climate outcomes from a single starting point in 1950. Running the models with and without the effects of greenhouse gas forcing factored in enables the scientists to separate the effects of natural cycles like El Niño from the effects of heat-trapping gases.

Douglas Kenney, director of the Western Water Policy Project at the University of Colorado, Boulder, said the projections reinforce the need for immediate actions to avert water shortages in the West, including massive conservation efforts, more efficient agricultural irrigation and rethinking how water from the region’s major rivers is allocated.

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