Rocky Mountain snow decline raises water shortage fears

Thursday 18th Aug 2011 by theWeather Cub

While stories and images of water shortage issues generally arrive on our screens from the tropical latitudes, recent figures show that the problem is not limited to these parts of the world, and ironically enough can be caused - amongst other reasons - by increased rainfall. A new study released by the United States Geological Survey (USGS) shows that the recent decline of the Rocky Mountains snow-pack witnessed since the 1980s is unusual when measured against the long term trend. Studies previously released by the USGS and other institutions have attributed this decline to several factors including unusual springtime warming, more precipitation falling onto the mountains as rain rather than snow, and an earlier snow melt.

The figures are of real concern as between 60-80% of the annual water supply for around 70 million people in the western US comes directly from winter snow-pack melting. With the decline in the snow-pack projected to worsen over the course of this century, scientists are beginning to worry about the amount of water that will one day be available.

“This scientific work is critical to understanding how climate change is affecting western water supplies,” US Secretary of the Interior Ken 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.”

In partnership with the Universities of Arizona, Washington, Wyoming and Western Ontario, the USGS led a study evaluating the recent declines in the snow-pack by investigating 66 tree-ring chronologies which looked back over 1,000 years. Throughout that time, with a few exceptions in the mid-14th and early 15th centuries, the snow-pack reconstructions showed that the northern Rocky Mountains generally experiences large snow-packs when the southern Rocky Mountains experience smaller ones, and vice versa.

However, since the 1980s there have been simultaneous declines along the entire length of the Rocky Mountains, with unusually dramatic declines in the north. “Over most of the 20th century, and especially since the 1980s, the northern Rockies have borne the brunt of the snow-pack 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 snow-pack 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.”

“The difference in snow-pack along the north and south changed in the 1980s, as the unprecedented warming in the springtime began to overwhelm the precipitation effect, causing snow-pack to decline simultaneously in the north and south,” explains USGS scientist and co-author Julio Betancourt. “Throughout the West, springtime tends to be warmer during El Niño than La Niña years, but the warming prior to the 1980s was usually not enough to offset the strong influence of precipitation on snow-pack.”

It is a sobering reminder of the complexity of our dependence on the climate, and the importance of further study so we have a clearer idea where climate change effects may appear in the future.