Columbia basin water supply drops again

The most recent water supply reports for the Columbia River Basin showed a continuing trend of deteriorating conditions due to warmer-than-average temperatures, below-average precipitation through much of the basin and a rapid, early runoff from mountain snowpack across the region.

“Things have definitely slipped downward since Jan. 1,” said Taylor Dixon of the Northwest River Forecast Center in Portland during a May 7 teleconference.

Dixon said the “big story” of the current water year are temperatures in Washington and Oregon that have deviated from 3 to 6 degrees above historic averages— and in some areas above 6 degrees — during the last few months.

“The temperatures are driving the volume forecasts this year,” Dixon said, adding that there has been more rain than snow through most of the basin, particularly in the lower basin, less snowpack accumulation, and a high and early runoff.

What has resulted are record-low streamflow forecasts for April through September in multiple watersheds: 44 percent of average for the Spokane River at Spokane; 35 percent of average for the Yakima River; 25 percent of average for the John Day River; 17 percent of average for the Grand Ronde River. The forecasts for all other rivers in the basin are considerably below average, but not at record lows. Forecasts for the Snake River at three locations, for instance, range from 55 to 67 percent of average.

West of the Cascades, there are widespread record-low forecasts through September: 64 percent of average for the Skagit River; 37 percent for the Dungeness River; 49 percent for the Cowlitz River; 43 percent for the Lewis River; 56 percent for the McKenzie River; 46 percent for the South Santiam River and the North Santiam River; 47 percent for the Willamette River; and 50 percent for the Clackamas River.

The combined effect of conditions in Columbia River tributaries is a forecast of flows being at 72 percent of average at The Dalles Dam on the main stem Columbia River, considered to be a choke-point barometer for basin-wide flows.

That is a substantial downgrade from a water supply forecast for The Dalles that was issued on April 9, predicting that flows would be at 82 percent of average through September.

On May 6, the Northwest Power and Conservation Council was briefed on the basin-wide water supply picture.

Jim Ruff, manager of main stem passage and river operations, also referenced the high temperatures, low snowpack and early runoff conditions.

Ruff told the council during its meeting in Portland that 76 percent of the automated snow measuring sites in Oregon recorded measurements that were the lowest on record over the winter. The only bright spots, he said, were at Snotel sites in the upper Columbia Basin in British Columbia and Montana, where snowpack measurements were near average.

Ruff said official droughts have been declared in eight Idaho counties, seven Oregon counties and 16 water resource areas in Washington.

He said there are officials who believe water supply conditions in the basin are related to an “extreme sea surface temperature anomaly” that has set up in Pacific Ocean waters off the West Coast. It has been referred to as a “blob” of warmer-than-usual water, and it is believed to be having adverse effects on marine life that could affect future salmon returns in the Columbia Basin.

For Ruff’s complete report to the Council, “Hydrologic conditions, water supply forecasts and drought declarations for the Columbia River” go to http://www.nwcouncil.org/media/7149197/6.pdf .

For more details on Northwest water supply outlooks for your area see the Northwest River Forecast Center at http://www.nwrfc.noaa.gov/rfc/ .