Drought effects on hydro generation differ across the West

Western region not a monolith of renewable energy generation

In 2021 drought affected much of the western United States, reducing consumer water supply and lowering hydropower generation in the Pacific Northwest and California.

Last year power generation from California’s hydropower plants was 48% below the 10-year average (2011–2020). In Washington, Oregon, Montana, and Idaho, hydropower generation was 14% below the 10-year average.

Precipitation, specifically rain and snowfall, that accumulate during the winter and early spring months impact the region’s water supply. On April 1, 2021 the California Department of Water Resources conducted a snow survey, reporting that snowpack in the Sierra Nevada mountain range was 41% below normal. The date is significant because it marks the time of year when the snowpack holds the greatest amount of water. In contrast, snowpack levels in the Pacific Northwest were close to normal, according to the National Weather Service (NWS) Northwestern River Forecast Center.

Extreme temperatures and heat waves also affected drought conditions in the western states in 2021.

The two largest reservoirs in California, Shasta Lake and Oroville Lake, supply water to two hydropower plants. The Shasta hydropower generating plant, California’s largest hydroelectric facility, was 46% lower in 2021 compared with the 10-year average.

Historic low water levels at Lake Oroville caused the Edward Hyatt hydropower plant to go offline for the first time in its 54-year history. Electricity generation in 2021 from the plant adjacent to Oroville dam was 81% lower than the 10-year average.

In the Pacific Northwest, electricity generation at the Columbia River’s Grand Coulee power plant, the largest hydroelectric facility in the U.S., was 12% below the 10-year average. Electricity generation at The Dalles hydropower plant, also on the Columbia, was 14% lower in 2021 compared with its 10-year average.

timeseries or graph of monthly hydropower generation (2016-2021) in million megawatthours | source: United States Energy Information Administration, Electric Power Monthly

source: U.S. Energy Information Administration, Electric Power Monthly