Decreased precipitation, increased evapotranspiration, and increased temperatures associated with climate change may decrease energy production in some regions. Production of electricity from fossil fuels, nuclear power, and hydropower requires adequate supplies of water. For generation methods that require steam, it takes about 25 gallons of water to generate 1 kWh of electricity. Water withdrawals for power plants represent the largest demand for fresh water in the United States, accounting for up to 41 percent of withdrawals in some regions. If water supplies are limited, the supply of electricity will be as well.
Hydroelectric power also requires sufficient water: reservoir levels must be high enough to provide the hydraulic head (liquid pressure) that drives turbines to generate electricity. Models suggest that a one percent decrease in precipitation would decrease water supplies enough to decrease hydropower generation by three percent. Changes in streamflow during different seasons may also reduce generation of electricity in the West because the hydropower process relies on seasonal snowmelt to provide steady outputs throughout the year.
Climate change is expected to result in decreased precipitation in at least one season for the Northwest, Southwest, Southeast, Midwest, and Great Plains, resulting in more frequent drought conditions and smaller volumes of water in streams and reservoirs. In the Northwest and Southwest, expected decreases in the portion of precipitation that falls as snow in the winter as well as drier conditions in the summer may decrease summer stream flows. In all regions, increased temperatures will increase the rate of evapotranspiration, leading to a decrease in surface water supplies in rivers and reservoirs.
In a warmer climate, increased water and air temperatures would also reduce the efficiency of electricity production. For thermoelectric power plants, a lack of cold water would decrease cooling efficiency, reducing capacity for electricity production. Increased water temperatures could reduce efficiency at these plants by one percent: this translates to a national decrease of 25 billion kWh each year that would need to be replaced by other sources. Elevated air temperatures can also affect certain types of electricity generation systems. For instance, a 10°F increase in air temperature can decrease efficiency of gas turbine electricity generation by three to four percent. Electricity generation by air-cooled geothermal energy sources may also be affected by higher air temperatures.
This section is excerpted and abridged from the report Climate Change Impacts in the United States: The Third National Climate Assessment (Chapter 2: Our Changing Climate, Chapter 3: Water Resources, and Chapter 4: Energy Supply and Use) and the report Effects of Climate Change on Energy Production and Use in the United States (PDF).