Record-breaking rain and snow in parts of the western United States have contributed to the US Energy Information Administration’s forecast 71% rise in hydropower generation in California this year compared with 2022, according to EIA’s latest Short Term Energy Outlook (STEO). However, below-normal precipitation and a mixed water supply outlook in the Pacific Northwest, which generates a significant portion of the country's hydropower, partly offset the forecast increase in hydropower generation in California.
The Pacific Northwest houses more than one third of US hydropower capacity and produces about half of the country’s total hydropower, on average. As a result, changes in hydroelectric supply in the Northwest can affect the region’s power markets, leading to changes in natural gas consumption and electricity trade with neighbouring states.
On 4 May, the National Oceanic and Atmospheric Administration’s Northwest River Forecast Centre (NWRFC) released its latest water supply forecast for the rest of the 2023 water year, which ends on September 30. The NWRFC forecasts normal to below-normal water supply for most of the Columbia River Basin and above-normal water supply in the southern part of the region around the Snake River Basin. NWRFC forecasts remain uncertain because more precipitation may fall in May and because warmer-than-normal temperatures may trigger snowmelt.
Seasonal precipitation and snowpack accumulation are the two main factors that predict water supply. The 2023 water year (1 October 2022 – 30 September 2023) followed a warm, dry summer in the Pacific Northwest. Extreme heat waves across Washington, Oregon, and Idaho left the region with dry soils and low runoff. The precipitation seen this past autumn and winter was mostly below normal, especially in Washington and northern Idaho.
However, some parts of the region have received significant precipitation. Atmospheric rivers that brought record levels of precipitation to California also arrived in southern Oregon and southern Idaho. This precipitation fell in the form of snow, even at lower elevations, because of colder-than-normal temperatures.
The NWRFC water supply forecast for The Dalles dam on the border between Washington and Oregon is 93% of normal, reflecting conditions in the upstream Columbia River system.
The NWRFC’s water supply outlook contributes to EIA’s May forecast in STEO of 14% less electricity generation in the Northwest from hydropower this calendar year compared with 2022. It expects that US hydropower plants will generate 260 million MWh of electricity this year, or 6.4% of total electricity generation.