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BOR Climate Impact Assessment For Columbia Basin: Runoff To Increase In Winter, Decline In Summer
Posted on Friday, April 01, 2016 (PST)

The Bureau of Reclamation, which operates Grand Coulee and Hungry Horse dams among others in the Northwest, released its Columbia River Basin Climate Impact Assessment last week. The report projects climate change impacts on water resources in Oregon, Washington, Idaho and Montana.


The study ( found that the basin will continue to experience warming temperatures throughout the basin and that precipitation timing will change significantly, although not necessarily the mean annual precipitation, the BOR said. In the future, there will be more precipitation during the winters and less during the summers.


"This climate impact assessment for the Columbia River Basin will give water managers new information to plan for sustainable water supplies now and into the future," said Estevan López, Reclamation commissioner. "This impact assessment is only the starting point – an initial analysis of conditions. This serves to establish a foundation for in-depth studies that will include more detailed climate adaptation strategies."


The report was released last week in conjunction with the first White House Summit on Water in observance of World Water Day. During the summit, the administration announced new efforts and commitments from the federal government and more than 100 external institutions to enhance the sustainability of water in the United States.




The assessment used five climate scenarios to simulate temperature, precipitation and runoff over four decades, the 2020s, 2040s, 2060s and 2080s. The five climate scenarios were less warming and wetter, less warming and drier, median, more warming and wetter, and more warming and drier.


Future climate change inflow data was calculated at 157 locations across the basin.


“With the warming temperatures and increased precipitation in the winter, runoff is expected to increase in the winter and decline in the summer,” according to the BOR.


Three areas were specifically studied, the Columbia River above The Dalles, the Snake River at Brownlee Dam and the Yakima River at Parker. At these three points the mean snow water equivalent is projected to decline at all locations. The assessment projected a trend that indicated there would be an increase in runoff from December to March and a decrease in runoff (in most projections) from April to July.


Some of the findings in the study include:


-- Changes in precipitation varied more widely than those for temperature, but mostly agreed in their simulation of increased precipitation during the cool season and decreased precipitation during the warm season.


-- As compared to temperature changes projected for the other subbasins considered in this Assessment, the Upper Snake River Basin exhibited the largest increases in temperature and followed the pattern seen in the other subbasins with the largest increases occurring during the summer months.


-- Almost all scenarios project increased precipitation during the winter.


-- Projected conditions for the remainder of the year (May through October) were more varied, but generally indicate drier conditions (decreased precipitation) during those months. Only the Less Warming/Wet scenario corresponded to year-round increases in precipitation.


-- Changes in temperature and precipitation will have important and varied consequences for water resources across the region, with hydrologic response (for example, timing and magnitude of runoff) depending upon the dominant form of precipitation in the basin and other local characteristics such as elevation, aspect, geology, vegetation, and changing land use.


The findings are not a surprise to people tracking climate trends worldwide and in the Northwest.


According to the report, earlier climate investigations have estimated that the basin’s average mean-annual temperature has increased by approximately 2 °F since the late 1800s.


“Also, while trends in precipitation have not been detected, the Columbia River Basin has experienced a general decline in spring snowpack since the mid-20th century due to more precipitation occurring as rain (rather than snow) and earlier snowmelt runoff,” the report said.


The Columbia River Basin Climate Impact Assessment is a part of a more comprehensive assessment known as the West-wide Climate Risk Assessments and is a complementary activity with the Basin Studies and the Landscape Conservation Cooperatives within the WaterSMART Initiative. Also studied were the Sacramento and San Joaquin river basins and the upper Rio Grande.

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