Yakima reservoirs defy drought, stay high

September 3, 2021
Yakima reservoirs defy drought, stay high

Yakima River Basin reservoirs in south-central Washington have held up during this year’s drought and heat and still contain more water than usual for this time of year, Bureau of Reclamation officials said Thursday.

Bumping, Cle Elum, Kachess, Keechelus and Rimrock reservoirs were at 48% of capacity Sept. 1, or 109% of normal. The reservoirs haven’t held that much water at the start of September since 2017.

The reservoirs should retain enough water to bode well for 2022, especially if a La Nina forms as expected and makes the upcoming winter cold and wet, officials said.

“It shows how important the snowpack and the reservoir storage is for the basin,” said Chris Lynch, the bureau’s river operations manager.

The reservoirs supply water to irrigate about 464,000 acres, according to the bureau. The Yakima basin was hit hard by the “snowpack drought” in 2015. Some irrigators were cut back by more than 50%.

This year, irrigators have had full water allotments, even though the U.S. Drought Monitor judges this year’s drought worse for the state as a whole.

Like the rest of Eastern Washington, the Yakima basin has been dry for months. The basin received 53% of normal rainfall from March through August.

The reservoirs, however, filled in the spring, fed by a larger than normal snowpack. Although the spring was dry, temperatures were mostly moderate, preventing the snow from melting too fast.

“That really was the saving grace of this season,” Lynch said.

The reservoirs peaked at nearly full on June 30, relatively late — and later is better for irrigators. Since then more water has been flowing out than in. Reservoir levels have remained relatively high, even though irrigation demand surged during high heat.

In late August, temperatures dropped closer to normal, Lynch said. “That really did help moderate the demand on the system and releases from the reservoirs,” he said.

“We were running around 115 to 120% of average releases from the reservoirs during that really hot stretch and now we’re back down near normal, even below normal at times,” Lynch said.

Lynch said he expects the reservoirs to hold roughly 315,000 acre-feet at the end of October, about the long-term average.

The odds favor a La Nina prevailing next winter, according to the National Oceanic and Atmospheric Administration. During a La Nina, Washington’s winters are usually cold and wet, building up snow in the mountains to melt into reservoirs in the spring.

“Combined with a healthy start in storage (in the reservoirs), it looks good,” Bureau of Reclamation hydrologist Mik Lewicki said.

The U.S. Drought Monitor on Thursday reported the 38% of Washington — all east of the Cascades — was in “exceptional drought,” the worst category.

This is the first year any part of the state has been classified in “exceptional” drought since the Drought Monitor began releasing weekly reports in 2000.

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