There’s more bad news for water watchers in the Rocky Mountain West, where record snowpack from last winter has led to a dangerous runoff in some places, including Colorado’s Western Slope. The bad news is this season is apparently a statistical blip in a 30-year historical decline in Rocky Mountain snowpack, which provide between 60 and 80 percent of the water supply for the 70 million people living in the western United States.According to a study released late last week by the U.S. Geological Survey (USGS), steady declines in Rocky Mountain snowpack over the past three decades are highly unusual when compared to previous centuries. USGS scientists teamed up with scientists at the University of Arizona, University of Washington, University of Wyoming and the University of Western Ontario to produce a study entitled “The Unusual Nature of Recent Snowpack Declines in the North American Cordillera,” which is available online at Science Magazine.
The report relied on snowpack reconstructions produced by studying 66 tree-ring chronologies dating back from 500 to more than 1,000 years. With the exception of the mid-14th and early 15th centuries, the snowpack reconstructions revealed that the northern Rockies saw larger snowpacks when the southern Rockies saw smaller ones, and vice versa. But over the last 30 years there were simultaneous declines in both the south and the north, with unusually big declines in the north.
“Over most of the 20th century, and especially since the 1980s, the northern Rockies have borne the brunt of the snowpack losses,” said USGS scientist Gregory Pederson, the lead author of the study. “Most of the land and snow in the northern Rockies sits at lower and warmer elevations than the southern Rockies, making the snowpack more sensitive to seemingly small increases in temperature. Also, winter storm tracks were displaced to the south in the early 20th century and post-1980s. Forest fires were larger, more frequent and harder to fight, while Glacier National Park lost 125 of its 150 glaciers.”
U.S. Interior Secretary Ken Salazar, a former Colorado senator, issued this statement on the USGS report:
“This scientific work is critical to understanding how climate change is affecting western water supplies,” Salazar said. “It helps land managers adapt to changing conditions on the ground, assists water managers with planning for the future, and gives all of us a better understanding of the real impacts that carbon pollution is having on our resources and our way of life.”
The news is apparently nearly as bad in the southern Rockies. A separate report recently produced by the U.S. Bureau of Reclamation in conjunction with seven states that rely on the Colorado River Basin (including Colorado), found water supplies in the basin may decline by up to 20 percent by the middle of this century. That’s produced a lot of hand wringing by water policymakers over the future of the 1922 Colorado River Compact, as chronicled today by veteran water reporter Allen Best of Mountain Town News.