Felicity Barringer: Snowmelt in the Rockies Just Isn’t the Same

Snowmelt in the Rockies Just Isn’t the Same

by Felicity Barringer, Green, The New York Times, June 10, 2011

(Jack Affleck/Associated Press) A new study by the geological survey confirms that Rocky Mountain snows, like these in the Ten Mile Range, consistently melted sooner over the last 30 years than they had in centuries past.

The summary of the new United States Geological Survey paper in Science was blunt. “Over the past millennium, late-20th-century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains,” it said.


The authors of the study, which was based on an analysis of 66 tree-ring studies, some of which gave a glimpse into conditions 800 or more years ago, added, “The increasing role of warming on large-scale snowpack variability and trends foreshadows fundamental impacts on stream flow and water supplies across the western United States.”


On the one hand, the underlying narrative was depressingly familiar, synchronizing with other studies or predictions involving California’s Sierra, the Himalayas and other spots around the world. What drew my attention is the reminder that snowmelt in the Rockies feeds three huge river systems — the Colorado, the Columbia and the Missouri — on which 70 million Americans depend for water.

Not that everyone living along — or flooded out of the communities along — the Missouri River or its swollen tributaries would consider these findings intuitive. But the U.S.G.S. scientists who led the study point out that climate in the Rocky Mountains has for centuries been an either-or proposition.


It works like this. Draw a hypothetical line in your mind from Denver to Salt Lake City to Sacramento. If there is heavy snow to the north of this line, chances are there will be a drought to the south of it. And vice versa. Or, as an Interior Department press release said, “With a few exceptions (the mid-14th and early 15th centuries), the snowpack reconstructions show that the northern Rocky Mountains experience large snowpacks when the southern Rockies experience meager ones, and vice versa.”


This year’s experience fits in with that trend, but in terms of the recent past, it’s an anomaly.
The press release quoted Gregory Pererson, the study’s lead author, as saying, ““Most of the land and snow in the northern Rockies sits at lower and warmer elevations than the southern Rockies, making the snow pack more sensitive to seemingly small increases in temperature.”
As a result, the pattern of north-wet-south-dry, south-wet-north-dry was disrupted in the last 30 years: while the northern Rockies got much warmer, the southern Rockies warmed as well. Snowpack declined in both sectors. This year’s snowy abundance, the press release said, represents no more than a “blip” in the long-term trend.


http://green.blogs.nytimes.com/2011/06/10/snowmelt-in-the-rockies-just-isnt-the-same/