Wildfires and slope instability

Many natural hazards such as earthquakes and cyclonic storms have distinct damaging effects and can serve as a trigger to landslide occurrence. The occurrence of damaging effects and landslides take place, more or less, contemporaneously. Wildfires are a natural hazard that causes an immediate damage by burning vegetation and flammable parts of the built environment. Rather than directly triggering landslides, wildfires alter the short-term susceptibility of slopes to gravity-related phenomena making debris flows more likely during later storm events. The papers presented in the “Wildfires and Slope Instability” session centered on two themes reflecting the difference in how and when slope instability is altered by wildfire occurrence. The first theme was assessing wildfire effects to forecast the likelihood of landslides, especially debris flows. The keynote address, “Characterizing the immediate and subsequent hazards caused by wildfire occurrence” examined recent advances in wildfire suppression and forecasting of debris flows. Wildfire suppression has improved through earlier detection using aerial and satellite-based systems and modeling which identifies times of greater wildfire likelihood and how active wildfires will advance. Similar advances exist for wildfire-related debris flows, especially the use of modeling to forecast debris flow potential, likely volumes to occur and probable paths where damage would occur. Another paper on this theme was “Remote sensing and geospatial support to burned area emergency response (BAER) teams in assessing wildfire effects to hillslopes”. The rapid identification of the varied impact of a wildfire to vegetation across the burned landscape is a key tool for determining potential secondary impacts including debris flow occurrence. Soil burn severity maps are quickly created through interpretation of spectral reflectance in satellite imagery and on-the-ground examination of soil in representative locations. The resulting GIS-based product is readily integrated with other geospatial data and models used to assess wildfire effects.