Effects of Climate Change on Hydropower — The Second 9505 Assessment
Hydropower is a key contributor to the US renewable energy portfolio due to the diverse benefits it provides to the electric power system. Ensuring the sustainable operation of existing hydropower facilities is of great importance to the US renewable energy portfolio and the reliability of the electricity grid. As directed by Congress in Section 9505 of the SECURE Water Act (SWA) of 2009 (Public Law 111-11), the US Department of Energy (DOE), in consultation with the federal Power Marketing Administrations (PMAs) and other federal agencies, has conducted a second 5-year assessment examining the effects of climate change on water available for hydropower at federal facilities and on the marketing of power from these federal facilities. This Oak Ridge National Laboratory Technical Memorandum, referred to as the “9505 assessment,” describes the technical basis for the report to Congress that was called for in SWA.
To evaluate climate change effects on the 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 is collected to support model development, calibration, and verification. 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.
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 will need to allocate water use more cautiously. 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 hence may continue to provide stable annual hydropower generation in the projected near-term and midterm 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 PMA study areas. This generalized approach allows for spatial consistency, enabling policy makers to evaluate potential climate change impacts across the entire federal hydropower fleet. This effort is expected to promote 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.
Public release of the report is pending delivery of the companion DOE report to Congress