The Impact of a Wildfire on a Vegetated Topsoil: Field Monitoring and Numerical Modeling

Wildfires are generally believed to be detrimental to slope stability by damaging vegetation and altering the thermo-hydro-mechanical properties of soil due to thermal stress and burning. However, the extent to which wildfires may impact on state of the vegetation and soil state is still an open issue, as it depends on several factors such as the fire intensity and persistence, as well as the soil and vegetation state and type. This research focused on a wildfire event that was monitored and back-analyzed using thermal finite element modeling by using Plaxis 2D to understand the impact on the soil post-wildfire state. The study was conducted at a field test site located at the toe area of the Pisciolo hillslope, where selected vegetation had been seeded and farmed to investigate the soil–vegetation–-atmosphere (SVA) interaction. The test site was the location of a wildfire in September 2023, which burnt most of the vegetation. The results show that the heat flux due to the wildfire is in the range between 100 and 150 kW/m² with a duration of 5–10 min. Field monitoring revealed that significant wildfire-induced temperature variations were confined to the near-surface soil layer, up to a depth of 20 cm of soil, with only slight changes in the soil properties.