COLUMBIA RIVER — The Columbia Basin is possibly looking at a summer with progressively diminishing water supplies, because of similar conditions that developed last year across the basin.
Mountain snowpacks were at or near average by mid-April in Washington, Oregon, Idaho, and Montana, but warm temperatures — in some cases record highs — fueled an early snowpack runoff that peaked on some waterways weeks ahead of historic expectations.
The Natural Resource Conservation Service issued reports for the four states in June that indicate similar outlooks for the rest of the summer.
The Oregon NRCS report states: “Current streamflow forecasts are calling for below-normal to well-below normal streamflow volumes across the state, which may signal water supply shortages for those water users who do not have access to reservoir storage.”
The report goes on to say, however, that the early runoff boosted reservoirs throughout the state.
“This brings a much better water supply story than compared to this time last year … Even so, if summer is hot and demand for reservoir water is high, water users drawing from reservoir sources could still experience tight water supplies near summer’s end.”
Most streamflow forecasts in Oregon from June through September range from 55 percent of historic averages to 85 percent of average. The outliers are the 36 percent of average forecast for the Silvies River near Burns, and 95 percent of average on the Deschutes River in central Oregon.
The Montana NRCS water supply forecast for drainages feeding the Columbia Basin, June through July are 70 percent of historic averages, but 143 percent of average compared to last year.
In Washington, the NRCS shows below average streamflows from May through September. Western Washington streams will be in the 90 to 99 percent of average range. Forecasts for eastern Washington streams are in the 75 to 90 percent range of historic averages.
The Idaho NRCS report from May predicts streamflow forecasts ranging from 70 to 90 percent of historic averages across most of the state, citing similar weather conditions discussed in reports from the three other states in the Columbia Basin.
(Editor’s Note: The Idaho and Washington Natural Resource Conservation Service forecasts are based on reports from May. Montana and Oregon are based on June reports.)