The Potential Impact of Regional Climate Change on Fire Weather in the United States

Climate change is expected to alter the frequency and severity of atmospheric conditions conducive for wildfires. In this study, we assess potential changes in fire weather conditions for the contiguous United States using the Haines Index (HI), a fire weather index that has been employed operationally to detect atmospheric conditions favorable for large and erratic fire behavior. The index summarizes lower atmosphere stability and dryness into an integer value with higher values indicting more fire-prone conditions. We use simulations produced by the North American Regional Climate Change Assessment Program (NARCCAP) from multiple regional climate models (RCMs) driven by multiple general circulation models (GCMs) to examine changes by midcentury in the seasonal percentage of days and the consecutive number of days with high (values ≥ 5) HI across the United States. Despite differences among the six RCM–GCM combinations in the magnitude and location of the projected changes, the results consistently suggest an increase in the number of days with high HI values over most of the United States during the summer season, with the dryness factor of the HI contributing more than the stability parameter to the projected changes. In addition, the consecutive number of days with high HI is projected to increase in summer. Together, these results suggest that future summers might be more conducive to large and dangerous fires. The projections for other seasons are inconsistent among the model combinations.