USGS Study Finds Recent Snowpack Declines in the Rocky Mountains Unusual Compared to Past Few Centuries

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From The Colorado Springs Gazette (R. Scott Rappold):

Researchers examined tree rings to look at moisture trends going back 500 to 1,000 years, in the first study to examine historic snowpack in this manner. While the northern Rockies have seen the most dramatic loss – less snow, earlier melt-offs – the southern Rockies, including Colorado, have experienced similar trends since the 1980s. That bucks the historical trend, that when the northern Rockies have more snow, the south has less, and vice versa. The recent drops are across the board, 30 to 60 percent of the snowpack.

The study comes at a time of heavy lingering snowpack in Colorado, 248 percent of the average for mid-June. But, said lead author Gregory Pederson, the average is based on recent years; the long view shows this winter may not be as out-of-whack as it seems. “There’s nothing unusual per se about this year, just that it comes in the midst of a lot of low-snowpack years,” he said.

He said the study, along with other research that has shown Western snowpack declines, should be a warning for water suppliers. The only similar periods occurred in the 1350s and 1400s, he said, and these were followed by colder, snowier eras. But, because of the impact of greenhouse gasses, Pederson does not believe that will occur again. “With increased warming, we may now be seeing this temperature impact on the snowpack, more of the precipitation falling as rain rather than snow,” he said…

[Colorado Springs Utilities Water supply planning supervisor Abby Ortega] said the fact the city’s water comes from three different basins insulates it from some of the problems of erratic snowpack. This year, for example, the Arkansas basin has less than half the snowpack of the other side of the Continental Divide, and Pikes Peak has been exceptionally dry.

More coverage from Dan Vergano Sci-Tech Today. From the article:

The historical snowpack reconstruction results, dating to the year 1200 and released by the journal Science, suggest that global warming has broken the normal seesaw pattern of snowpack in the region, in which a down year in the northern Rockies will be offset by a higher snow year in the southern Rockies. Overall, the average yearly snowpack across the northern Rockies directly known from snow records to have dropped 30% to 60% in the past 50 years has fallen more sharply in that time than for any period in the past 800 years, the study shows. “Temperature is the driver here,” says study lead author Greg Pederson of the U.S. Geological Survey’s Northern Rocky Mountain Science Center in Bozeman, Mont. “It doesn’t take a rocket scientist to know that if temperatures get warmer, snow and ice melt sooner.”[…]

The Northern Rockies stretch from Washington state to Montana. The study records show two-decade-long drops in snowpack across the northern Rockies in the 1300s and 1500s that resemble the decline seen in the 20th century, but those declines lasted for shorter periods of time and came when far fewer people were dependent on the snowpack. “Water demand, as much as supply, is the problem,” Pederson says. “We have a lot of fisheries and hydropower relying on this water as well.”

More Colorado River basin coverage here.

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