A two-decade study of wildfire activity across the western United States has found that heat waves — defined as three or more consecutive days of extreme heat — account for 42% of all land burned by wildfires, despite making up only 12–15% of warm-season days. Researchers found that daily burned area was more than 50% larger during heat waves than in the days preceding them, with some regions seeing increases of up to 300%, driven by rapidly drying vegetation, reduced nighttime humidity, and a rise in dry lightning ignitions. The findings carry growing urgency: heat wave days across western US forests have nearly doubled since 2001, and the authors estimate that without this increase, cumulative burned forest area over that period would have been 37% smaller.