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Study: Northwest Endured Worse Droughts

February 15, 2005

SEATTLE (AP) — The low snowpack in the Cascade Range is raising the specter of water shortages this summer, but a new study of tree-ring data indicates the Northwest has endured far worse droughts over the past 250 years – and is likely to again.

The study, published in the Journal of the American Water Resources Association, said the region endured six multiyear droughts between 1750 and 1950, including one that started in the 1840s and lasted for 12 years.

The authors – Dave Peterson of the U.S. Agriculture Department, Ze’ev Gedalof of the University of Guelph in Ontario, and Nate Mantua of the University of Washington’s Climate Impacts Group – said the evidence shows a need for better drought planning in the Northwest.

“We’ve built most of our infrastructure in the last half-century or so, but we haven’t had any major multiyear droughts during that time,” said Peterson, who also teaches at the UW’s College of Forest Resources. “The water has been overallocated. What do we do when we get into a five-year drought and everybody’s competing for water? We haven’t had to face that but we probably will.”

Farmers and hydroelectric facilities depend heavily on the water flow in the Columbia River, and enough water needs to remain in the river basin to provide habitat for salmon.

The three conducted the study by coring out samples of tree trunks from around the region, sanding them down and digitizing the information left by the tree rings – enabling them to see how much the trees grew each year. By comparing that to known information about the Columbia River’s flow since 1878, they were able to extrapolate how the level of the Columbia – essentially, how much rain and snow fell in a year – compared to tree growth.

They saw serious multiyear droughts in the 1840s and the 1930s – the latter a drought that, along with poor agriculture practices, caused the Dust Bowl.

“One of the things we have noted is that drought causes all kinds of conflict over limited water supplies,” Mantua said. “We still haven’t come up with a great collection of drought response plans in not just the Pacific Northwest, but throughout the West.”

The Northwest’s most recent drought was in 2001, but a more serious one – one that led to water restrictions even in rainy Western Washington – came in 1993. This year’s snowpack is far below average so far, but scientists are holding out hope for snow in March and April.




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