A laboratory-scale simulation framework for analysing wildfire hydrologic and water quality effects

Background Wildfires can significantly impact water quality and supply. However logistical difficulties and high variability in in situ data collection have limited previous analyses. Aims We simulated wildfire and rainfall effects at varying terrain slopes in a controlled setting to isolate driver-response relationships. Methods Custom-designed laboratory-scale burn and rainfall simulators were applied to 154 soil samples, measuring subsequent runoff and constituent responses. Simulated conditions included low, moderate, and high burn intensities (~100–600°C); 10-, 200-, and 1000-year storm events (~14–51 mm/h); and 10–29° terrain slopes. Key results Simulators can control key drivers, with burn intensities highly correlated (R2 = 0.64) with heat treatment durations. Increasing burn intensity treatments generally saw significant (α = 0.05) increases in responses, with runoff and sedimentation increasing by ~30–70% with each intensity increment. Carbon and nitrogen peaked at moderate intensities (~250°C), however, with concentrations ~200–250% of unburned samples. Conclusions Distinct responses at each burn intensity indicate nuanced changes in soil physical and chemical composition with increased heating, exacerbating driving mechanisms of runoff and sedimentation while reducing carbon and nitrogen through volatilisation. Implications This work furthers our understanding of interactions between complex geographic features and the mosaic of burn intensities which exist in wildfire-affected landscapes.