Effects of Climate Change on Hydropower — The Second 9505 Assessment

Lead Investigator
Shih-Chieh Kao

Participating Staff
Moetasim Ashfaq
Rocio Uría Martínez

Bonneville Power Administration
Southwestern Power Administration
Southeastern Power Administration
Western Area Power Administration

Water Power Technologies Office, US Department of Energy (DOE)

Start Date: 2013

End Date: 2016

Background and Objective
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, have conducted a second 5-year assessment 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. This Oak Ridge National Laboratory Technical Memorandum - "The Second Assessment of the Effects of Climate Change on Federal Hydropower," referred to as the second “9505 assessment,” describes the technical basis for the DOE Report to Congress "Effects of Climate Change on Federal Hydropower" that was called for in SWA.

To evaluate potential 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 are collected to support model development, calibration, and verification. Extending from the framework established in the first 9505 assessment, this second assessment now provides future seasonal and monthly hydropower projections to support long-term hydropower marketing planning.

Major Findings
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 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.

Use of the 9505 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. In addition, 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. This data set can be obtained by contacting the ORNL NHAAP Team.


DOE Report to Congress: US Department of Energy (2017), Effects of Climate Change on Federal Hydropower - The Second Report to Congress, US Department of Energy, Washington, DC.

9505 Technical Assessment: Kao, S.-C., M. Ashfaq, B. S. Naz, R. Uría Martínez, D. Rastogi, R. Mei, Y. Jager, N. M. Samu, and M. J. Sale (2016), The Second Assessment of the Effects of Climate Change on Federal Hydropower, ORNL/SR-2015/357, Oak Ridge National Laboratory, Oak Ridge, TN.

Dynamical Downscaling: Ashfaq, M., D. Rastogi, R. Mei, S.-C. Kao, S. Gangrade, B. S. Naz, and D. Touma (2016), High-resolution Ensemble Projections of Near-term Regional Climate over the Continental United States, J. Geophys. Res., 121, 9943–9963, doi:10.1002/2016JD025285.

Hydrologic Modeling: Naz, B. S., S.-C. Kao, M. Ashfaq, D. Rastogi, R. Mei, and L. C. Bowling (2016), Regional Hydrologic Response to Climate Change in the Conterminous United States Using High-resolution Hydroclimate Simulations, Global Planet. Change, 143, 100–117, doi:10.1016/j.gloplacha.2016.06.003.

Other Studies Using 9505 Hydro-climate Projections:
Mani, A., F. T.-C. Tsai, S.-C. Kao, B. S. Naz, M. Ashfaq, and D. Rastogi (2016), Conjunctive Management of Surface and Groundwater Resources under Projected Future Climate Change Scenarios, J. Hydrol., 560, 397–411, doi:10.1016/j.jhydrol.2016.06.021.

Pagán, B., M. Ashfaq, D. Rastogi, D. Kendall, S.-C. Kao, N. S. Naz, R. Mei, and J. S. Pal (2016), Extreme Hydrological Changes in the Southwestern U.S. Drive Reductions in Water Supply to Southern California by Mid Century, Environ. Res. Lett., 11(9), 094026, doi:10.1088/1748-9326/11/9/094026.

Schubel, J., J. A. Lentz, F. Qader, A. Kishaba, D. Bader, L. Perkins, E. Yam, A. Kaneda, L. Brown, B. R. Pagán, J. S. Pal, C. Gao, J. Reichenberger, D. R. Kendall, M. Ashfaq, D. Rastogi, S.-C. Kao, B. S. Naz, and D. Otto (2015), City of Long Beach Climate Resiliency Assessment Report, prepared by the Aquarium of the Pacific (AOP), for the City of Long Beach, CA.