The snow pack in the Rocky Mountains provides far more than excellent skiing. Melted snow from the Rocky Mountains supplies drinking water for about 70 million Americans, but a study by the U.S. Geological Survey warns that warmer springs have reduced snow cover in the mountains by 20 percent since 1980.

The decline in snow cover was most extreme in the north. Snow cover was also significantly reduced in the low and middle latitudes.

Reductions in snow cover and changes in the timing of the annual melt also threaten electricity production from hydroelectric dams as well as irrigation water. The changes may also alter the risks of fire and flood in the American West.

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“Each year we looked at temperature and precipitation variations and the amount of water contained within the snow pack as of April,” said lead author and USGS scientist Greg Pederson in a press release. “From 1980 on, warmer spring temperatures melted snow pack throughout the Rockies early, regardless of winter precipitation. The model in turn shows temperature as the major driving factor in snow pack declines over the past thirty years.”

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A model created by USGS scientists used monthly temperature and precipitation data from 1895 to 2011 to paint a picture of the variations in Rocky Mountain snow cover. This allowed them to separate natural variations, such as El Niño cycle influences, from those related to human-caused climate change. The results were recently published in Geophysical Research Letters.

“Regardless of the ultimate causes, continuation of present snow pack trends in the Rocky Mountains will pose difficult challenges for watershed management and conventional water planning in the American West,” said co-author Greg McCabe of the USGS in a press release.

IMAGE: The Colorado Rocky Mountains (T. H. Painter, Snow Optics Laboratory, JPL/Caltech, NASA)