Wildfire Effects on the Geotechnical Properties of Soils: A State-of-the-Art Review

Wildfires are becoming increasingly common in most parts of the world, posing significant risks to both the natural and built environment. Evidence also suggests that climate change is intensifying the frequency and severity of these events. While the ecological and environmental impacts of wildfires have been thoroughly discussed, there is currently a lack of literature pertaining to their effects on the geotechnical properties and behaviors of soil, despite increasing evidence of their significance. This paper seeks to address this gap by presenting a state-of-the-art review of wildfire impacts and characterization methods, with particular emphasis on their implications in geotechnical engineering. Key concepts in wildfire characterization such as fire intensity and burn severity are discussed and the distinction between the two is highlighted. Various methods to assess burn severity are compared and the lack of standardization across approaches is raised. The review then discusses wildfire-induced changes in some key soil properties such as cohesion, internal friction angle, grain-size distribution, hydraulic conductivity, and hydrophobicity. Inconsistent trends in changes of these properties due to variability in pre-burn conditions, soil types, and fire characteristics are highlighted and the reasons for these inconsistencies are theorized. Furthermore, we identify key knowledge gaps in the existing literature and suggest potential avenues for future studies. We highlight the need to develop a burn severity criterion for geotechnical engineering applications as well as further investigations into wildfire-induced subsequent natural hazards such as landslides and erosion.