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 (http://www.usbr.gov/watersmart/wcra/docs/cbia/ColumbiaBasinImpactAssessment.pdf)
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
"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
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
-- 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
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.