The role of drought in the persistence of post-fire hydrologic hazards

Drought influences both the susceptibility of landscapes to wildfire and how post-fire landscapes recover. In erodible steeplands, the post-fire environment creates the potential for hydrologic hazards including flash floods, debris flows, and shallow landslides. Recent work has shown that the rate of landscape recovery governs the probability of these hazards in the years following fire. However, how drought influences recovery rates remains an open question. To evaluate how various drought characteristics influence post-fire recovery in 12 burn areas spanning three Southwestern mountain regions, we utilize four-day 500 m resolution MODIS-based leaf area index (LAI) in tandem with daily estimates of precipitation, reference evapotranspiration, and standard multiscalar drought indicators such as the standardized precipitation-evaporation index to evaluate recovery trajectories across a range of post-fire weather and climate conditions. We then use temporal variations in LAI to parameterize temporal changes in hydrologic model parameters to quantify how different recovery trajectories influence the persistence of hydrologic hazards. We find that while recovery to pre-fire LAI may not occur within 10 years, burn areas experience varied rates of recovery within the first five years following fire. The rates can either be independent of, or well-correlated to, single to multi-year year drought metrics depending on the timing and magnitude of precipitation delivery. To address this complexity, we propose a framework to continuously monitor recovery rates at subseasonal timescales and utilize simulation-based approaches to rapidly assess how post-fire hazard probabilities evolve through time.