Mortality Attributable to Drought, Wildfire Smoke, and Their Concurrent Added Effects in the Contiguous United States

Climate change has led to more frequent individual and concurrent drought and wildfire smoke events in the U.S., yet whether their concurrence adds to health burden remains understudied. We assessed the frequency of these events, developed a Two-Step Individual and Added Effect Estimation (TIAE) Model to evaluate their effects, and estimated the attributable mortality across 3,103 U.S. counties from 2007 to 2023. We identified annual averages of 3,630 county-months (∼110,342 county-days) of drought, 14,049 county-days of wildfire smoke, and 980 county-days of concurrent exposure. Both individual events were significantly associated with increased all-cause mortality, with a significant added effect observed during concurrent days. We estimated 6,576 (95% CI: 3,990, 9,155), 10,465 (95% CI: 6,642, 14,261), and 469 (95% CI: 256, 682) annual deaths attributable to drought, wildfire smoke, and their added effect, respectively, with a higher burden in counties with higher overall social vulnerability index. These findings call for targeted measures to address the burden from drought, wildfire smoke, and their concurrence.