Stability Analysis of Unsaturated Slopes Stricken by Wildfires

Climate change has led to more severe and frequent droughts, creating more fuel to sparkle more wildfires worldwide. Wildfires are now occurring more frequently, at higher severity, and higher elevations. Adverse impacts of wildfires accumulate by post-fire geohazards, such as shallow landslides that may occur due to fire-induced changes in soil and land cover. This study aims to develop an analytical framework to evaluate the stability of wildfire-stricken slopes subjected to heavy rainfalls. An analytical framework for transient infinite slope stability analysis of variably saturated soils is developed by employing a closed-form solution of the Richards equation to capture water flow in slopes while considering the transpiration effect. The proposed model captures the effects of initial soil conditions, time-varying rainfall intensity, and wildfire-induced changes in soil mechanical and hydraulic properties, root reinforcement, and transpiration rate. The model is used in a set of parametric studies to examine the effect of soil type, burn severity, slope angle, and soil thickness. It is demonstrated that fire could decrease the factor of safety to rainfall- triggered landslides by up to 20%. The proposed model uses measurable landscape characteristics and hydro-mechanical properties of soils and can be used in developing landslide hazard maps for wildfire-prone areas.