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July 8, 2020

Mixed water supply conditions affect summer 2020 hydropower outlook in Pacific Northwest

Columbia River Basin water supply forecast by monitoring station
Source: U.S. Energy Information Administration, based on National Oceanic and Atmospheric Administration, Northwest River Forecast Center

On June 4, the National Oceanic and Atmospheric Administration’s Northwest River Forecast Center (NWRFC) released its final Pacific Northwest water supply projection for the 2020 water year, which runs from October 2019 to September 2020. The forecast shows above-average water supply in the northern half of the Columbia River Basin and below-average supply in the southern half, the opposite of last year’s forecast. The below-average supply in the southern half could reduce electricity available from hydropower in the lower Columbia River Basin this summer.

More than one-third of the nation’s hydroelectric capacity is located in the Pacific Northwest. Grand Coulee, the largest hydropower facility in both the Columbia River Basin and the United States, generates enough electricity to power 4.2 million households. Because of hydropower’s significance and variability, the water supply forecasts for this region are closely monitored. Changes in water supply, and subsequently hydroelectric generation, in the Pacific Northwest can have implications for the use of other electricity-generating fuels in the region and electricity trade with neighboring areas.

Snowpack and seasonal precipitation levels are the main factors in the water supply forecast. Snowpack, or accumulated winter snowfall, can indicate how much water will be available to power hydroelectric generators throughout the year as meltwater flows through the river basins.

In addition to precipitation and winter temperatures, soil moisture in the months preceding snowfall contributes to water supply. In September 2019, the month preceding the start of the 2020 water year, the majority of reporting stations in the Columbia River Basin recorded precipitation levels at more than 130% higher than the 30-year normal. The wet September drove up soil moisture levels, contributing to the preservation of the region’s snowpack in the following months.

Columbia River Basin precipitation

Seasonal precipitation levels drive the NWRFC forecast. To date, seasonal precipitation in the northern half of the Columbia River Basin is approaching near-normal levels, following strong storms at the beginning of the year. In January, atmospheric rivers, which are long, narrow bands in the sky that move large amounts of water vapor, drenched parts of the northern Columbia River Basin with rain and snow, which increased water supply.

Conversely, the southern half of the Columbia River Basin is experiencing below-normal seasonal precipitation levels, and most of the reporting stations in Oregon were lower than 70% of normal. These differences in seasonal precipitation are reflected in the regional differences in the water supply forecast for April through September.

The Dalles Dam is a run-of-river hydroelectric plant located near the mouth of the Columbia River. Because of its location, hydro operators consider water flow at The Dalles an indicator for the entire upstream Columbia River system. Although water flow at The Dalles is often used to represent water supply in the basin as a whole, it does not capture regional variation in water supply across the basin. As of June 4, the NWRFC projects The Dalles Dam water supply forecast for April through September to be 100.1 million acre-feet, approximately 8% higher than the 30-year normal (1981–2010).

Because water supply and the subsequent hydroelectric generation can vary widely from year to year, water supply forecasts are closely monitored and used as inputs to the U.S. Energy Information Administration’s Short-Term Energy Outlook (STEO). The July 2020 STEO forecasts that hydroelectric generators will provide 285 million megawatthours in 2020. About half of that total comes from hydro plants in the Northwest. Overall, hydroelectricity is expected to account for 8% of U.S. electricity generation in 2020.

monthly hydropower electricity generation by region
Source: U.S. Energy Information Administration, Short-Term Energy Outlook, June 2020

Principal contributor: Michelle Bowman