Minghao Qiu , Nathan Ratledge, Ines Azevedo, Noah S Diffenbaugh, Marshall Burke

The western United States has experienced severe drought in recent decades, and climate models project increased drought risk in the future. This increased drying could have important implications for the region's interconnected, hydropower-dependent electricity systems. Using power-plant level generation and emissions data from 2001-2021, we quantify the impacts of drought on the operation of fossil fuel plants and the associated impacts on greenhouse gas emissions, air quality, and human health. We find that under extreme drought, electricity generation from individual fossil fuel plants can increase up to 65% relative to average conditions, mainly due to the need to substitute for reduced hydropower. Over 54% of this drought-induced generation is trans-boundary, with drought in one electricity region leading to net-imports of electricity and thus increased pollutant emissions from power plants in other regions. These drought-induced emissions increases have detectable impacts on local air quality, as measured by proximate pollution monitors. We estimate that the monetized costs of excess mortality and greenhouse gas emissions from drought-induced fossil generation are 1.2-2.5x the reported direct economic costs from lost hydro production and increased demand. Combining climate model estimates of future drying with stylized energy-transition scenarios suggests that these drought-induced impacts are likely to remain large even under aggressive renewables expansion, suggesting that more ambitious and targeted measures are needed to mitigate the emissions and health burden from electricity sector during drought.