After water levels at a California dam fell to historic lows this summer, the main hydropower plant it feeds was shut down. At the Hoover Dam in Nevada — one of the country’s biggest hydropower generators — production is down by 25%. If extreme drought persists, federal officials say a dam in Arizona could stop producing electricity in coming years.

Severe drought across the West drained reservoirs this year, slashing hydropower production and further stressing the region’s power grids. And as extreme weather becomes more common with climate change, grid operators are adapting to swings in hydropower generation.