Compilation and re-analysis of post-wildfire soil hydraulic properties across climate zones of the western United States

Abstract:

Under our changing climate, wildfires are increasing in size and frequency in regions where they have historically been less common or severe. These areas are also experiencing increased risk, and in some cases, new exposure to, post-wildfire hazards such as runoff-initiated debris flows. One such region is the coastal Pacific Northwest, where fire severity has increased over the last two decades and the first runoff-initiated debris flow was reported in 2018 (Wall et al., 2020). Hence, there is a need for additional study into climate effects on post-wildfire soil hydrology and associated hazards. Rainfall infiltration is a key factor in both landscape development and generation of rainfall-runoff hazards. In many arid to semi-arid landscapes, rates of infiltration can be reduced significantly by moderate to high severity burning, which in turn enhances run-off and contributes to debris flow hazard. However, it is currently unknown if these documented post-fire perturbations apply uniformly across climate zones. We hypothesize that the difference in regional climate manifests as a difference in post-wildfire infiltration behavior. We have compiled and re-analyzed new and existing post-wildfire soil hydraulic property datasets from different climate zones across the western United States. We examined these re-processed datasets in conjunction with both established climate zones and a variety of precipitation metrics known to influence post-wildfire hazards, including rainfall intensity at several timescales. Results from this work will help incorporate newly fire-prone areas into future post-wildfire modeling efforts.