After reaching a 20-year low for the 2020–21 water year, hydropower production in the western United States increased slightly during the 2021-22 water year, rising 13% to reach 161 million megawatt-hours (MWh).
Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming, California, Oregon, and Washington produced 82% of the nation’s hydroelectricity last water year according to the U.S. Energy Information Administration (EIA).
However the three largest hydropower-producing states in the region — Washington, Oregon, and California — are credited for producing 61% last year. Data from the NOAA NWS Northwest River Forecast Center and the California Department of Water Resources (DWR) show that increased precipitation in the 2021–22 water year fueled the increased electricity generation in these states.
Hydropower generation in Montana, Idaho, and Colorado was relatively unchanged; however, “well-below-normal flow rates in the Lower Colorado River reduced generation in Arizona and Nevada” according to EIA. The Hoover Dam generated 10% less hydroelectricity than it did in the previous water year because of the historic low water level of Lake Mead.
Western hydroelectric generation can vary significantly year over year because it depends on rain and snowfall. A water year covers the 12-month period from October 1 through September 30. The water year follows the water cycle; precipitation in the fall or early winter does not affect stream and river flows until the following spring and summer.