An 800-year history of the layers of snow, or snowpack, across the northern Rocky Mountains reveals that this particular snowpack has been decreasing at an almost unprecedented rate for the last 50 years. And, since runoff from the snowpack feeds the Colorado, Columbia and Missouri Rivers — the primary water sources of more than 70 million people — the discovery raises questions about how global warming might affect both water supply and water security in the future.
Gregory Pederson and colleagues used a network of 66 different tree-ring chronologies to reconstruct the growth and shrinkage of the northern Rocky Mountains snowpack over the past eight centuries. They found that the snowpack shrunk more during the late 20th century than during any other period of time since 1200 AD. The researchers also note that the see-saw-like behavior of the snowpacks in both the northern and southern Rockies, which used to balance the level of snowpack between the regions, became uncoupled sometime during the 1980s.
In light of their findings, the researchers say that temperature has probably replaced precipitation as the dominant influence on snowpack in the Rocky Mountains over the last few decades. If this proves to be true, the researchers say it could have significant implications for future water supplies across the warming, western United States. This research appears in the 09 June 2011 issue of Science Express.
Source: American Association for the Advancement of Science
