At the turn of the 20th century, as the United States developed the West, the federal government built hundreds of hydroelectric dams on major rivers in the region. These dams destroyed river ecosystems and flooded Indigenous land, but they also provided a cheap and abundant source of renewable energy for tens of millions of people. Hydropower today meets around a quarter of the region’s energy needs.

But the hydroelectric fleet in the West has taken a beating over the past 20 years as a series of devastating droughts have battered the area. When major rivers dry up, less water flows through hydroelectric dam turbines — and dams produce less electricity as a result. At the same time, the heat waves that often accompany dry periods lead to more demand for power as people crank up their air-conditioning. That’s bad news for grid operators, who have to find an alternate source of electricity just as dams are falling short.

This decline in hydropower leads to a significant surge in fossil fuel emissions, according to a new study published last week in the Proceedings of the National Academy of Sciences, a leading scientific journal. After looking at power generation across the West between 2001 and 2021, the authors of the study found that coal and gas plants ramped up their activity during dry months to replace lost hydropower, leading to more carbon emissions and more local air pollution. While that finding was expected, the scale of the increase in fossil fuel emissions surprised the researchers.

“The effect on the power mix is actually pretty large,” said Minghao Qiu, a postdoctoral scholar at Stanford University who is the lead author of the study.

Read the full article about hydropower loss in Western states by Jake Bittle at Grist.