Climate Change Could Reduce River Flows

Photo Courtesy of Koree Tate

CORVALLIS, Ore. — A new study of river basins in the western U.S. suggests that climate change will have the greatest impact on summer stream flows.

The study concludes that Oregon’s major rivers, such as the Willamette, McKenzie, Deschutes, Klamath and Rogue may be among the most sensitive to climate change.

“These are big rivers fed by snow that enters deep groundwater systems with highly permeable geology,” said Mohammad Safeeq, a post-doctoral researcher at Oregon State University.

Safeeq says that the average summer flows of Cascade streams are two centimeters lower, or about a 36 percent decline.

Gordon Grant, a research hydrologist with the Pacific Northwest Research Station of the U.S.D.A. Forest Service says research managers shouldn’t panic.

“Oregon will continue to have plenty of water in the future,” Grant said. “But, it is important to acknowledge that even these big, bountiful rivers will be affected by climate change and that may have an impact on everything from power generation, to irrigation and fish survival.”

Researchers studied the daily stream flow of 81 watersheds across the western U.S. from 1950 to 2010. They focused on the drainage efficiency of rain-driven and snow-driven systems.

Areas with steep slopes and relatively impermeable rocks, such as the Coast Range or older Cascades, causes rain to rapidly run off the land. This results in high flows in winter and very little water in summer. Researchers say climate change won’t affect summer stream flows much because they’re already more or less dry in the summer.

In snow-driven systems such as volcanic areas of the high Cascades, the heavy snowfall melts, seeps into the porous underlying rock and slowly moves into major river systems. In a warming climate, where there will be less snow and earlier melt in the spring, the slow journey would cause the rivers to drop for longer periods and result in lower late-summer flows.

“Slow-draining, snow-driven river systems may appear to be less affected by climate change, but they are in fact most sensitive to change,” said Safeeq.

Grant says the geology of the landscape and its effect on how fast water moves is just as important as knowing how much snow and rain will fall.

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