September 10, 2009

Pacific Northwest: Dry years getting drier

The U.S. Forest Service says it has determined the Pacific Northwest's dry years are becoming drier as a result of climate change.

Forest Service researchers Charlie Luce and Z.A. Holden said most recent studies of annual streamflow in the Pacific Northwest have looked at mean or median streamflows and have found little or no change during recent decades. But Luce and Holden say it's important to know the severity of dry spells -- a subject that has not been studied as thoroughly.

The researchers analyzed 1948-2006 runoff data from 43 Forest Service stations in the Pacific Northwest and found that while few stations had significant declines in median or mean streamflow, most stations recorded significant declines in streamflow during the driest 25 percent of the years.

The scientists conclude dry years have been getting substantially drier and water managers who must cope with water scarcity and its ecological consequences will face increasing challenges as the trends continue.

The study is reported in the journal Geophysical Research Letters.