Impacts of changing fire weather conditions on reconstructed trends in U.S. wildland fire activity from 1979 to 2014

One component of climate‐fire interactions is the relationship between weather conditions concurrent with burning (i.e., fire danger) and the magnitude of fire activity. Here daily environmental conditions are associated with daily observations of fire activity within ecoregions across the continental United States (CONUS) by aligning the latter 12 years of a 36 year gridded fire danger climatology with the Moderate Resolution Imaging Spectroradiometer fire products. Results reveal that although modern relationships (2003–2014) vary regionally, fires across the majority of CONUS are more likely to be present and burning more vigorously as fire danger increases. Applying modern relationships to the entire climatology (1979–2014) indicates that in the absence of other influences, changes in fire danger have significantly increased the number of days per year that fires are burning across 42–49% of CONUS (by area) while also significantly increasing daily fire growth and daily heat release across 37–45% of CONUS. Increases in the fire activity season length coupled with an intensification of daily burning characteristics resulted in a CONUS‐wide +0.02 Mha yr −1 trend in burned area, a 10.6 g m −2  yr −1 trend in the amount of fuel consumed per unit burned area, and ultimately a +0.51 Tg yr −1 trend in dry matter consumption. Overall, the results demonstrate regional variations in the response of fires to changes in fire danger and that weather conditions concurrent with burning have a three‐pronged impact on the magnitude of fire activity by affecting the seasonal duration, spatial extent, and combustion intensity.