Led by Fa, a recent publication in PNAS Nexus titled “Exacerbating risk in human-ignited large fires over western United States” sheds light on the significant role human activities play in intensifying wildfire risks across the western U.S. The study reveals that large fires ignited by humans occur under conditions with lower flammability thresholds and experience way more flammable days compared to those ignited by lightning.
These findings underscore the need for targeted fire management strategies that address human-induced ignition sources. By understanding the distinct characteristics of human-ignited fires, policymakers and land managers can develop more effective prevention and mitigation approaches to reduce the frequency and severity of wildfires in vulnerable regions.
For a comprehensive understanding of the study’s methodology and implications, the full article is accessible here: PNAS Nexus Article.
Lower VPD thresholds and more flammable days for human-ignited large fires. The spatial distribution of the ecoregions in the western United States a), the differences in the constraints of VPD on the probability of human- and lightning-ignited large fires in each ecoregion b), and the mean annual number of flammable days from 1979 to 2020 c). In b), lines of the same color represent the response curves of large fire probability to VPD within the same ecoregion for human-ignited (dashed lines) and lightning-ignited fires (solid lines). Shaded ribbons in b) denote the 90% credible intervals for the probability of large fires limited by VPD. The inset within b) displays the VPD thresholds at the 90% probability level of the VPD–large fire logistic function (see Materials and methods). Each point in c) signifies the mean annual number of flammable days (when VPD > VPDt) in a grid cell (0.25°). The whiskers in c) represent the 5th and 95th quantiles, with boundaries indicating the 25th, 50th, and 75th quartiles.