A new study released by the U.S. Geological Survey last week reports that snowpack in the Rocky Mountains has declined by unusual levels over the past three decades.
Moreover, projections indicate further warming in the region and more severe snowpack declines are expected throughout the 21st century.
Snowpack has been disappearing from areas already plagued by droughts, like the Colorado, Columbia, and Missouri River Basins, as warmer temperatures continue to melt more snow than accumulates annually through precipitation.
Unusually warmer springs have triggered earlier snowmelts, and also led to more rainfall than snowfall in the region.
Because the runoff from the Rockies’ winter snowpack provides 60 to 80 per cent of the annual water supply for more than 70 million people in the U.S. West, researchers are anticipating a strain on the local water supply if winter snow accumulation continues to decline.
Data from the USGS study “may signal a fundamental shift from precipitation to temperature as the dominant influence on western snowpack,” according to Gregory Pederson, lead author of the study.
USGS scientists and researchers from several western universities drew their conclusions largely from the analysis of various tree ring patterns.
Sixty-six tree ring chronologies examined from a “network of sites” were used to reconstruct snowpack levels dating back 500 to 1,000 years.
As Tasha Eichenseher of National Geographic News explained, “narrow rings indicate years of slow growth and meager water supply. Based on the predominance of narrow rings more recently, ‘the last 20 to 30 years were more intense than the last 800’ in terms of snowpack loss.”
The trees studied were chosen “strategically to characterize the range of natural snowpack variability over the long term, and from north to south in the Rocky Mountains.”
The snowpack reconstructions showed that historically when the northern Rockies accumulated larger snowpacks, the southern range had “meager” accumulations. The converse was also evident.
Since the 1980s, however, simultaneous declines in snowpacks were evident in both the northern and southern ranges, with unusually severe declines in the north.
The USGS study corroborates findings from other research that shows that as much as 60 per cent of the decline in snowpacks has been attributed to greenhouse gas emissions.
By the mid-21st century, the “average yield of the Colorado River could be reduced by 10 to 20 per cent due to climate change,” reported David Williams of The Colorado Independent.
“Meanwhile, the Basin States include some of the fastest growing urban and industrial areas in the United States. Increasing demands coupled with decreasing supplies will exacerbate imbalances throughout the Basin in the future.”
The U.S. Bureau of Reclamation is expected to publish a report by July 2012 with various approaches outlined for collaborative solutions to “inevitable conflicts” over a more limited water supply between affected Western states and user groups, from residents to industrial farmers and more.
Denver Water, a public water supply agency, has yet to detect an overall decrease in their water supply, however, “they are already dealing with the undeniable fact that snowpack is melting earlier,” reports National Geographic.
Marc Waage, a manager of resource planning at the agency, said that earlier spring melts are not as dire as an overall decrease in water supply since methods are available for capturing snow melt.
Waage did say, according to Eichenseher, that the USGS findings could serve as “an impetus” to plan with foresight for probably future droughts.
Photo credit: flickr.com/photos/jeffk/26156467/sizes/m/in/photostream/