Impact of anthropogenic climate change on wildfire across western US forests
The authors quantified the contribution of past anthropogenic climate change to increases in area burned based on observed increases in fuel aridity metrics from 1979 to 2015, including temperature and vapor pressure deficit.
The interannual variation of each of the eight fuel aridity metrics, reference potential evapotranspiration (ETo), VPD, climatic water deficit (CWD), Palmer drought severity index (PDSI), fire weather index (FWI) from the Canadian forest fire danger rating system, energy release component (ERC) from the US national fire danger rating system, McArthur forest fire danger index (FFDI), and the Keetch–Byram drought index (KBDI), were all significantly correlated to annual area burned of forested lands from 1984-2015.
Increasing trends toward aridity were found for all eight of the climate metrics used in the study. The authors found that anthropogenic climate change had the strongest signal tied to VPD and evapotranspiration, which are highly dependent on temperature. The anthropogenic climate change signal was weak for PDSI and ERC, whose values are driven primarily by precipitation. When the fuel aridity metrics were averaged, anthropogenic climate change accounted for 55% of the increasing trend from 1979 – 2015. Furthermore, the authors observed a 3.3-fold difference in the area burned between 1984 to 1999 and 2000 to 2015. Finally, the authors found an increase in the fire season length of 17 days of high fire potential since 1979 of which anthropogenic climate change accounts for ~45% of the increase. The authors state that the influence of anthropogenic climate change will continue to increase areas burned due to project increases in aridity unless fuel become limiting.