Environmental

PNNL determines U.S. hydropower generation should rise, but climate change brings uncertainty

PNNL determines U.S. hydropower generation should rise, but climate change brings uncertainty

In a study assessing how climate change might alter hydropower generation across the continental U.S., researchers with Pacific Northwest National Laboratory showed that except for some parts of the Southwest, generation is expected to rise in the future.

The analysis also shows that in the Pacific Northwest, less water will be stored in the mountains as winter snowpack as warmer temperatures bring more rain. This seasonal shift will challenge water managers and grid operators to rebalance how and when to produce electricity.

“We know the climate is changing and we know that’ll affect how much water will be available to produce hydropower,” said Daniel Broman, a hydro-climatologist at PNNL and lead author on the new paper. “Our research provides a consistent look across the country, so even if water and energy planners are only looking ahead regionally, our data can provide a broader outlook.”

How climate change affects hydropower

Water flows through 2,250 hydropower facilities across the U.S., contributing 6% of the country’s electricity. Dam operations don’t just consider power but also consider flood control, transportation routes, and water for irrigation and to support fisheries and natural ecosystems. Understanding how water availability will change is important for water managers when planning for their various resource needs.

To support this planning, the U.S. Department of Energy periodically the 9505 Assessment (referring to Section 9505 of the SECURE Water Act). The report provides a detailed assessment of climate change’s effects on hydropower facilities. The third of these reports was delivered to Congress in December 2023.

But that report only includes 132 facilities, all federally owned. The power they generate makes up 46% of the nation’s hydropower capacity, said study coauthor Nathalie Voisin, chief scientist for water-energy dynamics at PNNL. To better understand effects across the entire continental U.S., the researchers added streamflow and hydropower generation data from an additional 1,412 non-federal facilities.

They teamed up with colleagues at Oak Ridge National Laboratory, who have developed models that show how climate change might alter the timing and volume of water flow in streams and rivers. The PNNL team then ran that water flow data through models that captured the multiple uses of water and calculated hydropower generation for two time periods 2020 to 2039 and 2040 to 2059.

The team found that hydropower production generally increases about 5% in the near term and 10% in the mid term. This could be because climate models generally show an increase in precipitation as Earth warms.

Only one part of the country saw an average decrease in hydropower generation: in some parts of the Southwest, which is facing drought, the models project a decrease in hydropower production of 3% to 6% in the near term.

Broman stressed that because the future of climate change is uncertain, the range of possible outcomes for hydropower generation is large. For example, between 2020 and 2039, hydropower generation could change between –5 and 21%, while in later years it could change –4 to 28%.

Hydropower changes by season

Seasonal changes could also have big implications for how water is managed, Broman said.

In the winter, the team found that hydropower generation may rise 12% in the near term and 18% in the mid term. Similarly, increased rainfall during the fall may lead to a near-term 5 to 20% rise in hydropower production in the Southeast, as well as smaller increases in the Northeast and Midwest.

But some of the biggest hydropower generation changes may occur in the summer. Hydropower generation may decrease 1 to 5% in the western region of the country, while higher precipitation may increase hydropower generation in the eastern areas by 1 to 5%, both in the near-term.

Historically, mountain snowpack in the West has stored water until the late spring and summer. Now, less snow accumulates on mountains and melts earlier in the year. The early snowmelt and shift toward rain in the winter means hydropower generates more electricity during the winter and less in the spring and summer.

The future of hydropower

Voisin stressed that hydropower generation still offers a reliable source of energy for the power grid. Hydropower can be dispatched as needed and provide stability to the grid as a whole — highlighting its flexibility as a renewable energy source.

Broman and Voisin hope that power system operators and water managers can use the new consistent multiscale assessment and the accompanying data to inform water-energy tradeoffs discussions, such as hydropower flexibility needs amid other societal benefits of water uses.

This work was supported by DOE’s Office of Energy Efficiency & Renewable Energy’s Water Power Technologies Office as a part of the SECURE Water Act Section 9505 Assessment. PNNL is operated by Battelle for DOE’s Office of Science.