Historical droughts in the Columbia River Basin were more severe than anything in recent memory, including the drought of 1992-93, scientists said Monday.
A study of tree rings found four droughts between 1750 and 1950 that were "much more severe than anything in recent memory" because they persisted for years.
One drought that started in the 1840s lasted 12 years. Flows on the Columbia River were at least 20 percent below long-term averages and might have been much lower, said lead author Ze'ev Gedalof of the University of Guelph in Ontario. Reliable river flow records go back only about 75 years. But tree-ring data reveals how much trees grow each year, a reflection of climate.
"Imagine what a drought lasting that long would do to the resources and economy of the region today," says Dave Peterson of the U.S. Forest Service and the University of Washington's College of Forest Resources.
Five other multiyear droughts were identified, around 1775, 1805, 1890, 1925, and one in the 1930s coinciding with the Dust Bowl era.
The study was published recently in the Journal of the American Water Resources Association.
The study is a microcosmic look at one drainage. But other research has reached similar conclusions.
A much broader study covering the western United States and going back 2,000 years suggests that droughts in recent memory are indeed relatively minor.
That work, also based on tree-ring data and published in October, revealed that an ongoing drought in much of the Southwest has not achieved the level of aridness revealed in history. The current drought "pales in comparison with some of the earlier droughts we see from the tree-ring record," said David Meko, a University of Arizona researcher. "What would really put a stress on society is decade-long drought."
A 2003 report from UCLA found that Canada's Saskatchewan River system "may be prone to more prolonged and severe droughts than previously thought," based on tree rings dating back 1,000 years.
"Past droughts and corresponding declines in river flow have been worse than anything we've seen for the past 100 years," said UCLA researcher Roslyn Case.
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