Drought Impacts on Hydroelectric Power Generation in the Western United States

Researchers at Pacific Northwest National Laboratory (PNNL) are examining the historical hydroelectric generation data to understand the resilience of the western hydropower fleet during extreme drought. A new report details their findings based on more than two decades of data recorded at over 600 hydroelectric power plants across 11 states.

Drier conditions, such as those pictured here at Hoover Dam, could affect future hydroelectric power generation in the region.

(Photo by Katarzyna Przygodzka | Shutterstock.com)

Key report findings:

Figure 1. Drought in 2021	Diversity in weather conditions across the West makes for a resilient hydropower fleet Drought rarely affects all major hydropower regions of western United States at the same time. As a result, the overall western hydropower fleet sustains about four fifths of the average power generation during severe droughts. That translates to approximately 140 TWh of electricity in a severe drought year, which is commensurate with the combined electricity output from all other renewable resources in the West.
Figure 2. Drought in 2022	Western hydropower is set to rebound in 2022 Despite continued drought, the total hydropower generation in the West will increase in 2022 compared to 2021. The rebound is driven by healthy water resources in the Northwest. California and the Southwest remain in severe drought.
Figure 3. Drought in 2001	The drought beginning in 2020 impaired western hydropower generation, but prior droughts had a greater impact Drought beginning in 2020 and continuing through 2021 led to the second worst year for total hydropower generation in western United States this century. The year 2001 remains the worst year for western hydropower this century, owing to the extremely dry conditions in the Northwest, where about half of the western hydropower capacity is located. The drought of 1977 is the most severe hydropower drought of the last century. If a drought of that magnitude were to occur again, such an event could result in the loss of about one-quarter of the average annual western hydropower generation.
Figure 4. Drought in 2015	Drought affects hydropower generation differently across the many climatic regions in the western United States Identified in the report are eight distinct hydropower climate regions in the West. The analysis revealed that the worst hydropower drought years varied by region. Six different years were identified as the worst hydropower drought years for specific regions in the West (see Figure 5).

Figures 1-4. All images depict drought in the western United States, with darker colors indicating increased drought severity. Data are from the U.S. Drought Monitor. (Figures by Sean Turner | Pacific Northwest National Laboratory).