In its latest Short-Term Energy Outlook (STEO), the U.S. Energy Information Administration (EIA) forecast that electricity generation from U.S. hydropower plants in 2024 will be 13% less than the 10-year average, the least amount of electricity generated from hydropower since 2001.
“Extreme and exceptional” drought conditions have been affecting different parts of the United States, particularly the Pacific Northwest, which hosts the majority of U.S. hydropower capacity. By the end of September, 72.6% of the continental United States was experiencing dryer-than-normal to exceptional drought conditions, according to the U.S. Drought Monitor. By the end of October, this value increased to 87.2%.
Multiple regions are affected by drought conditions, but the effects on hydropower generation are more obvious in the Pacific Northwest, EIA notices. A recent study conducted by the University of Alabama found that hydropower generation in Washington is amongst the most susceptible to droughts in the country, ranking right below California based on data from 2003 to 2020.
As early as April of this year, the Washington State Department of Ecology declared most counties in the state to be under drought. The department takes this step when the water supply in the state is less than 75% of normal. In Oregon, two counties declared a drought emergency this summer, first in June in Jefferson County and then in September in Lake County.
The Dalles Dam located between Oregon and Washington, with a total net summer capacity of 1.8 GW, is generally considered an indicator of water supply conditions in the upper Columbia River. At the end of September, its water supply was at 74% of the 30-year normal for the summer months, according to the Northwestern River Forecast Center.
According to the U.S. Department of Agriculture’s Basin Outlook Reports, reservoir storage at the end of September was 48% of capacity in Oregon, 67% of capacity in Washington, 76% in Montana, and 60% in Idaho.
On a monthly basis in 2023, across Washington, Oregon, Idaho, and Montana, hydropower generation has been close to or below the lower end of the 10-year range, except for a brief spike in May due to a heatwave. In Washington and Oregon, hydropower generation in 2024 was mostly higher than in 2023, especially during the summer months. In Idaho and Montana, hydropower generation in 2024 was below 2023 levels from April through August.
In the STEO, the EIA forecasts electricity generation for electricity market regions instead of state geographical boundaries. It expects hydropower generation in the Northwest electricity region, which includes the Columbia River Basin and parts of other Rocky Mountain states, to total 101.8 billion kilowatt hours (kWh) in 2024, a 23% decrease from the 10-year average of 132.8 billion kWh and a 1% decrease from 2023.
Last month, the U.S. Army Corps of Engineers announced that September runoff in the upper Missouri River Basin was well below average, continuing the trend of below-average runoff in 2024. The six mainstem hydropower plants on the Missouri River generated 878 million kWh of electricity in September. Typical energy generation for September is 901 million kWh. The power plants are projected to generate 8.1 billion kWh of electricity this year, compared to the long-term average of 9.4 billion kWh.
Except for central Montana, which received greater than 150% of normal precipitation in a few days during late September, widespread areas of the upper Missouri River Basin received less than 25% of normal precipitation. According to the Sept. 24 drought monitor, over 81% of the Missouri River Basin is under abnormally dry or drought conditions. As a result, September runoff was 0.8 million acre-feet (MAF), 66% of the average above Sioux City. The updated 2024 calendar year forecast for the upper basin above Sioux City is 23.5 MAF, 91% of average, and 18.3 MAF above Gavins Point Dam, 79% of average. The average annual runoff for the upper basin above Sioux City is 25.7 MAF.
Outside the U.S., in its 2023-24 annual report, Manitoba Hydro reported a consolidated net loss of $157 million for the fiscal year ended March 31, 2024, compared to a consolidated net income of $638 million the previous year. The utility attributed this result to a drop in hydro generation due to drought conditions. About 97% of Manitoba’s electricity is generated from clean hydro, with most of the remaining 3% coming from wind generation.
