Hydropower is a key contributor to the nation’s renewable energy portfolio because of the diverse benefits it provides to the electric power system. Ensuring the sustainable operation of existing hydropower facilities is therefore of great importance to the United States. As directed by Congress in Section 9505 of the SECURE Water Act of 2009 (Public Law 111-11), the US Department of Energy—in consultation with the federal power marketing administrations and other federal agencies—is conducting a series of assessments examining the potential effects of climate change on water available for hydropower at federal facilities and on the marketing of power from these federal facilities.
To evaluate potential climate change effects on 132 federal hydropower plants in the United States, a spatially consistent assessment approach was designed to enable interregional comparisons. This approach uses a series of models and methods with different spatial resolutions to gradually downscale the global climate change signals into watershed-scale hydrologic projections to support hydropower impact assessments. A variety of historic meteorologic and hydrologic observations, hydropower facility characteristics, and geospatial data sets are collected to support model development, calibration, and verification. The second assessment now provides future seasonal and monthly hydropower projections to support long-term hydropower marketing planning.
The US Department of Energy’s Oak Ridge National Laboratory conducted the first round of 9505 Climate Change Impact Assessments from 2010 to 2012, and the second round from 2013 to 2017. The third round of 9505 assessments is currently underway and covers 2018 to 2022, with a targeted report to Congress in late 2022. The assessments will be further extended to nonfederal fleets from 2021 to 2023 to understand the climate change impacts on US hydropower generation at the national scale.
Among most of the federal hydropower plants throughout the United States, the most important climate change effect on hydrology is likely to be the trend toward earlier snowmelt and change in runoff seasonality. Under the projections of increasing winter–spring runoff and decreasing summer–fall runoff, water resource managers may need to consider different water use allocations. Given that most US federal hydropower reservoirs contain relatively large storage capacities, the system will likely be able to absorb part of the runoff variability and thus may continue to provide stable annual hydropower generation in the projected near-term and mid-term future periods. Nevertheless, the findings are based on the assumption that there is no significant change in future installed capacity and operation. The issues of aging infrastructures, competing water demands, and environmental requirements may reduce the system’s ability to mitigate runoff variability and increase the difficulty of future operation. These issues are not quantitatively analyzed in this study.
This study presents a regional assessment at each of the 18 power marketing administration study areas. This generalized approach allows for spatial consistency, enabling policymakers to evaluate potential climate change impacts across the entire federal hydropower fleet. This effort promotes a better understanding of the sensitivity of federal power plants to water availability and provides a basis for planning future actions that will enable adaptation to climate variability and change. Furthermore, the downscaled hydroclimate projection data set has also been used by multiple researchers and water resource planners to explore various aspects of climate change impacts on water and energy resources in the United States. The future hydroclimate projection data set can be obtained by contacting the Oak Ridge National Laboratory HydroSource Team.