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June-August Driest and Warmest in Washington, Idaho by CBB Staff Columbia Basin Bulletin, September 19, 2003

An abnormally hot and dry summer that has parched soils and plants has Columbia Basin water users praying for rain, rain, rain -- followed by a heavy mounding of mountain snow.

The bulk of the moisture that moves fish and commerce up and down the Columbia/Snake River basin, feeds agricultural crops and fuels hydroelectric turbines is accumulated over the winter. But a June-August period that was calculated to be the driest on record in Washington state and warmest ever in Idaho has served to sap the basin landscape.

Precipitation across Washington (recorded at 32 stations) averaged only 1.09 inches of rain for the three-month period. The next driest summer was way back in 1919 when only 1.43 inches fell. The average for the period (1971-2001) is 4.05 inches.

"We're talking about losing a couple of inches of rain. That's just a few days (of normal precipitation in western Washington) in December," said Philip Mote, the state climatologist. But it has had its effects, reducing streamflows to levels even lower than their normal low September levels. Other evidence of a relatively parched landscape is a state department of Natural Resources assessment that the moisture content in the state's forests is as low as it has ever been in 20 years of monitoring.

"We dodged a bullet there," Mote said of what has been a relatively mild wildfire season to-date.

The weather pattern has pretty much gripped the entire region. Calculations done by Mote indicate that both Idaho and Oregon precipitation totals this year are likely among the 10 lowest on record.

Evaporation from the soils and water bodies were higher than normal because of higher than average summer temperatures. Washington's average was 2.2 degrees higher than normal for the summer period, making it the sixth highest average on record. Mote said an average of Idaho, Oregon and Washington temperatures for June through August would be "the second warmest ever in the 100-plus years of record keeping." The combined precipitation average would be the third lowest behind 1919 and 1910.

"Southern B.C. was also quite dry," Mote said of the Canadian region from which the Columbia flows.

Precipitation, as recorded at about 50 Columbia River basin sites above the Dalles Dam, was the lowest in a 26-year record during July, as well as the lowest on record for either the June-July or July August periods, according to Nancy Stephan, supervisory meteorologist for the Bonneville Power Administration.

The region came out of the winter, and a relatively wet spring, with a water supply of slightly below average. The Northwest River Forecast Center's June 9 "final" runoff forecast for the January-July period was 89.3 million acre feet, about 83 percent of the average or "normal" outpouring of 103.8 MAF. The actual 2003 runoff for the period was 87.7 MAF, down in large part because of rainfall above The Dalles that was within .01 of an inch of matching the record low for June.

The August runoff into the Columbia system was the fourth lowest in a 74-year record, Stephan said. A few minor storm systems have rumbled through the region in early September but those rains have had little effect on streamflows.

"The soil conditions are so dry" any rainfall is immediately being absorbed, Stephan said.

Lingering drought conditions, and heat, have made water an even more precious commodity than normal in Idaho, particularly in the eastern and southeastern parts of the state.

A federal biological opinion calls for 427,000 acre feet of water to be released from Bureau of Reclamation irrigation storage facilities on the upper Snake River annually to augment in-stream flows for migrating salmon and steelhead. A dozen Columbia/Snake basin stocks are listed under the Endangered Species Act. The transactions are done on a willing seller basis with water rights holders shifting unneeded water into a rental pool for flow augmentation.

This year, the Bureau managed to find only about 268,000 acre feet. Most of came from the Boise and Payette systems, which had summer runoff at about 80 and 90 percent of average, respectively, said Bill Ondrechen, a hydrologist with the Idaho Department of Water Resources. Areas above Twin Falls, and Idaho Fall were not so lucky, with 70 percent or less of average runoff.

"They pretty much will use up all of the water this year," Ondrechen said of irrigators in those areas, who normally contribute about 200,000 of the salmon flows. "It was a minimally adequate year."

Those regions have remained in a moisture deficit since the severe drought of 2001. Runoff for the three-year period at Heise, which is below Palisades Reservoir and above most of the irrigation diversions, has been lower than any three-year period on record, Ondrechen said.

The summer's searing heat as wrung soils dry. Boise set a record both for total number of days above 100 degrees and consecutive says above 100 degrees.

The heat prompted above normal water consumption for crops, further taxing the system. Ondrechen used as an example a monitored alfalfa cop near Pocatello that required nearly 7 more inches or irrigation water (36.8 inches as compared to an average of 30) than normal.

Rains are sorely needed this fall before weather cools and the snows begins. The upper Snake has essentially received only three years worth of average precipitation over the past four years.

"We're still not catching up. We're still in deficit," Ondrechen said. "We're going to take more than one year to bounce back to normal, unless it's an exceptional year.

The summer was warm and dry, said Oregon climatologist George Taylor. But then summers are always warm and dry. He expects that surface soil moisture contents and reservoir will be renewed, as is normally the case, during the rainy, snowy winter season.

He has forecast normal to above normal precipitation for his state during the coming fall and winter.

Related Sites:
Flow Augmentation on Lower Snake River, 1987-2002 Idaho Department Water Resources
Sending Water Downstream for Fish, by Jennifer Sandmann, Times-News 9/6/3