Hydropower can ‘drive up CO2 emissions’

Climate change is driven by CO2 emissions and so non-emitting energy sources such as hydropower are seen as much preferred alternatives to coal-fired power plants. Yet hydropower dams, too, can drive up CO2 emissions significantly during times of drought when they cannot operate efficiently or at all, explains a team of scientists at Stanford University in the United States.

In the states of California, Idaho, Oregon and Washington, the scientists say in a study, droughts between 2001 and 2015 resulted in about a tenth of average CO2 emissions annually from power generation.

“Water is used in electricity generation, both directly for hydropower and indirectly for cooling in thermoelectric power plants,” notes climate scientist Noah Diffenbaugh, a professor at Stanford’s School of Earth, Energy & Environmental Sciences who was the senior author. “We find that in a number of western states where hydropower plays a key role in the clean energy portfolio, droughts cause an increase in emissions as natural gas or coal-fired power plants are brought online to pick up the slack when water for hydropower comes up short,” he added.

Diffenbaugh and his colleagues discovered that droughts, which put hydropower dams out of action, caused an extra 100 million tons of carbon dioxide to be releases across 11 states in the western part of the U.S. between 2001 and 2015. California, which seeks to become a carbon-free state, alone contributed around 51 million tons. That 100 million tons is a vast amount that equals adding 1.4 million vehicles each year to the region’s roadways, they observe.

“For California, Oregon and Washington, which generate a lot of hydropower, the drought-induced increases in carbon dioxide emissions represent substantial fractions of their Clean Power Plan targets,” says Julio Herrera-Estrada, a said postdoctoral researcher who was lead author of the study.

Troublingly, droughts are set to become increasingly more common in western states in the United States as a result of climate change, making hydroelectric power less of an appealing option locally. In recent years there have been several prolonged droughts in the area, which indicates that policymakers should start diversifying local low-carbon energy generation options by relying more on solar, wind and nuclear energy.

“To have reliable and clean electricity, you have to make sure you have an energy portfolio that’s diverse, such that low-emissions electricity sources are able to kick in during a drought when hydropower cannot fully operate,” Herrera-Estrada explains.