Skip to main content

Effects of Climate Change on Hydropower

9505 Assessment
Shasta Dam and Lake in California (credit: U.S. Bureau of Reclamation)


Hydropower is a key contributor to the nation’s renewable energy portfolio, helping to fill in the gaps between traditional sources of electricity and intermittent renewable sources such as wind and solar. However, as climate change results in more extreme weather events across the United States — particularly droughts in the west — it is crucial to better understand and predict the conditions that impact sustainable hydropower electricity generation and what operational changes can be made to mitigate these impacts.

The latest information about how these trends are evolving can be found in a Congressional report recently released by the U.S. Department of Energy’s Oak Ridge National Laboratory, which details its findings from its third climate change impact assessment for hydropower. The report is part of a series produced during a multi-year study directed by the SECURE Water Act of 2009 Section 9505.

In consultation with the federal power marketing administrations and other federal agencies, ORNL led a series of assessments for 132 federal hydropower plants across the United States to examine the potential effects of climate change on water available for hydropower generation and on the marketing of power from these federal facilities.

A spatially consistent assessment approach was designed to enable interregional comparisons. This approach used a series of models and methods with different spatial resolutions to gradually downscale global climate change signals into watershed-scale hydrologic projections to support hydropower impact assessments. In the first of three assessments, a variety of historic meteorologic and hydrologic observations, hydropower facility characteristics and geospatial data sets were collected to support model development, calibration and verification. The second assessment provided future seasonal and monthly hydropower projections to support long-term hydropower marketing planning. Finally, the third assessment adopted a multimodel assessment framework to better reveal the uncertainties in future hydrologic and hydropower projections. During each assessment, the latest climate projection information from the Coupled Model Intercomparison Project was used to support the modeling and analysis.

ORNL conducted the first 9505 Climate Change Impact Assessment from 2010 to 2012, and the second assessment from 2013 to 2017. The third assessment was conducted from 2018 to 2022.


Several potential risks that may impact the resilience of future federal hydropower generation were identified:

  • Hydrologic extremes continue to intensify. The intensification of future hydrologic cycle and extreme events was found to be one of the most critical issues threatening the resilience of power systems and infrastructure. Both historical observations and model projections suggest the intensity, frequency and magnitude of extreme rainfall events will continue to increase, which will likely challenge conventional reservoir management practices. Furthermore, the duration and severity of extreme drought events are also projected to increase in many parts of the United States. The ongoing megadrought in the western United States resulted in an unprecedented disruption to the water supply and hydropower generation, demonstrating the dire impacts of drought.
  • The timing of available supply and peak demand is increasingly coming into conflict. Temperature-driven early snowmelt is projected in most of the western United States, suggesting the bulk of runoff may arrive earlier in the spring. However, as informed by the energy demand analysis, more temperature-driven water and energy demand is expected to shift from winter to summer, which creates a conflict. Although, ideally, one may expect to mitigate this conflict through reservoir management, the intensified hydrologic extremes combined with all other competing water management objectives will limit the ability and flexibility to store more water resources to meet peak demand. Furthermore, in arid regions, the enhanced reservoir evaporation may result in a sizable reduction in storage and further exacerbate the nexus of electricity demand and water availability.

Overall, the results suggest that maintaining operational flexibility remains a key challenge for federal hydropower reservoirs. Although long-term average annual runoff and hydropower generation are projected to slightly increase across the United States, the uncertainty in the projections is large and suggests less runoff and generation in some seasons and regions. Increasing operational and marketing flexibilities would be highly valuable for all PMAs, if operational directives allow.


This study presents a regional assessment at each of the 18 PMA 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 may be used by 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 from ORNL’s HydroSource.

Next Steps

Continued, more in-depth studies and data support are underway. DOE issued a Request for Information to understand climate data and research needs to support nonfederal hydropower stakeholders and particularly small utilities that may not have sufficient resources to model and evaluate climate risks. Additional workshops and stakeholder engagement meetings will be organized to discuss future research and development initiatives.

Reports and Data