Low Elevation Watersheds will be Affected by Global Warming, Researchers Say

New research suggests that by the middle of the century, the McKenzie River watershed in Oregon's Cascade Mountains will lose more than half of the water stored in packed snow on the mountains.

The researchers point to global warming as the main factor is the watershed loss and suggest that similar impacts may be seen on low-elevation maritime snow packs around the world.

Oregon State University researchers project a 3.6 degree Fahrenheit temperature increase, which they report will bring special risks to many low-elevation mountain regions where the difference between precipitation as snow or rain is only the matter of few degrees in temperature.

If precipitation falls as rain rather than snow, it will not be stored on the mountains in snow pack, which the OSU researchers report may lead to "significant impacts" on a variety of components within the region, including natural ecosystems, agriculture, hydropower, municipal water supply and summertime recreation.

"In Oregon we have a water-rich environment, but even here we will have to manage our water resources differently in the future," said Eric Sproles, who led this study as a doctoral student at OSU.

"In the Willamette River, for instance, between 60-80 percent of summer stream flow comes from seasonal snow above 4,000 feet," he said. "As more precipitation falls as rain, there will more chance of winter flooding as well as summer drought in the same season. More than 70 percent of Oregon's population lives in the Willamette Valley, with the economy and ecosystems depending heavily on this river."

Annual precipitation in the future could be higher or lower than current norms, the researchers said, noting that it could change as much as 10 percent in either direction. But the OSU study pinpoints temperature as the driving force behind snowpack, far more than precipitation.

As temperatures rise the watershed is projected to lose more than 80 days of snow cover in an average year at certain elevations, the researchers report.

Their evaluation of the Oregon watershed can be applied to similar regions around the world.

"This is not an issue that will just affect Oregon," said Anne Nolin, a professor in the College of Earth, Ocean, and Atmospheric Sciences, and co-author of the study. "You may see similar impacts almost anywhere around the world that has low-elevation snow in mountains, such as in Japan, New Zealand, Northern California, the Andes Mountains, a lot of Eastern Europe and the lower-elevation Alps."

The study is said to be one of the most precise of its type done on an entire watershed. It is published in the journal Hydrology and Earth System Sciences, with support from the National Science Foundation.