Report: Fire Weather

Climate change is worsening wildfires across forested land and lengthening wildfire seasons in the Western United States. Warming from heat-trapping pollution is drying out forests, grasslands and other landscapes, increasing the likelihood that destructive fires will erupt and spread. And warming is also affecting day-to-day weather in ways that this analysis shows are increasing the frequency of fire weather days.

To explore changes in weather conditions that increase the spread of fire, Climate Central analyzed data from weather stations in 225 locations across 17 states going back to 1973. This review of historical trends in fire weather—a combination of high heat, low humidity, and strong winds—aims to investigate how climate change is affecting wildfire risk throughout the American West.

Long-term warming trends lead to accelerated evaporation from soils and plants, creating drier conditions. Our analysis of the U.S. West shows that this drying has been driving increases in the frequency of fire weather days, affecting states from the Pacific Coast to the western Great Plains and from the Canadian to the Mexican borders. In addition to increasing the risk of fire to communities throughout these states, these extreme conditions are also causing problems even when fires don’t ignite. In response to high-risk fire weather conditions, and in the hopes of avoiding equipment- related ignitions, power companies are shutting off electricity to millions of people, creating health risks to those who depend on power for refrigeration of medications and to stay cool during heat waves.

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