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Today in Energy

December 4, 2015

Pacific Northwest electricity mix influenced by weather conditions, El Niño

graph of net monthly electric power generation from hydropower and natural gas in Washington and Oregon, as explained in the article text
Source: U.S. Energy Information Administration, Electric Power Monthly

In the summer of 2015, hydroelectric generation in Washington and Oregon, which provides the largest share of electricity generation in the Pacific Northwest, was lower than normal, causing an increased reliance on natural gas and other fossil generation to meet electricity demand. A forecasted El Niño cycle may further complicate weather impacts on electricity generation during the coming months by extending the pattern of warmer, dryer weather.

Hydroelectric generation in the Pacific Northwest fluctuates throughout the year, typically peaking during the spring, as the melting snowpack (winter accumulation) fuels hydroelectric plants. However, last winter, much of the region experienced higher-than-average winter temperatures, causing more precipitation to fall as rain instead of snow. This change in the type of precipitation prevented snowpack from forming. By May 2015, Washington's and Oregon's snowpack had dropped to just 16% and 11% of their 30-year average, respectively. Instead of peaking in the spring, hydroelectric generation peaked in the winter and fell in the spring. Hydroelectric generation remained low throughout the summer, about 32% lower than the average of the previous five summers (2010–14).

Natural gas was among the fuels used to make up for the shortfall in hydroelectric generation. In May 2015, power generated by natural gas exceeded the range from the previous five years, and in July reached 3,307 thousand megawatthours—a 53% increase over July 2014.

This cycle of earlier-than-anticipated hydroelectric generation followed by increased natural gas generation may be repeated this winter. The National Oceanic and Atmospheric Administration (NOAA) is projecting that El Niño conditions may continue the warmer, dryer weather pattern in the Pacific Northwest into 2016. NOAA's three-month seasonal outlook for December 2015 through February 2016 indicates a high probability of above-average temperatures in the Pacific Northwest and coastal regions of California. Above-average temperatures are expected overall, but with a slightly lower probability, in other West Coast regions. The outlook indicates a high probability that Southern California will experience above-average precipitation and a slightly lower probability that the Pacific Northwest will experience below-average precipitation.

NOAA's winter outlook has mixed implications for overall West Coast hydroelectric generation. For hydroelectric generation to rise, increased precipitation must occur in watersheds feeding into hydroelectric facility reservoirs. The Columbia River Basin, which feeds many of the hydroelectric dams in Washington and Oregon, largely falls in a higher-temperature, lower-precipitation outlook area. Greater precipitation may be expected in Southern California, but fewer than half of California's reservoirs are located in the southern part of the state. More information on the location of major hydroelectric and other generation plants is available on EIA's U.S. Energy Mapping System.

maps of three-month outlook for temperature and precipitation, as explained in the article text

Principal contributors: Michelle Bowman, Danielle Lowenthal-Savy, Scott Bradley