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Missing mountain water

Date: August 13, 2015

Declining precipitation and streamflow in northwestern U.S. mountains and forests may be related to changes in westerly winds


Scientists previously attributed earlier and lower streamflows solely to warming temperatures. A recent scientific study on high-elevation climate trends over a 60-year period in the mountains of the Pacific Northwest suggests that an alternative mechanism – decreases in mountain precipitation driven by decreases in winter winds across the region – may compound expected declines in streamflow. Warming related to an increased atmospheric CO2 may have contributed to the changed atmospheric pressure patterns that result in reduced wind speeds.

Understanding mechanisms that result in lower streamflows are important because mountains are a primary water source in the Pacific Northwest. Less precipitation leads to reduced runoff for communities, industry and agriculture. Decreased precipitation also exacerbates early snowmelt tied to warming temperatures. Acknowledging the effects of decreasing precipitation requires changes in how resource specialists approach climate change adaptation for water resources and forest management compared to preparing for increased temperature alone. This may present important implications for changes in mountain precipitation and future water availability for other regions as well. 

Precipitation declines in mountains, associated with declines in winter westerly winds, are a primary driver of declining runoff and streamflow in mountain rivers over the last half-century (Photo by Charles Luce).
Precipitation declines in mountains, associated with declines in winter westerly winds, are a primary driver of declining runoff and streamflow in mountain rivers over the last half-century (Photo by Charles Luce).

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Principal Investigators: 
Forest Service Partners: 
Zachary Holden, Northern Region
External Partners: 
John Abatzoglou, University of Idaho, Department of Geography