An integrated framework for wildfire emergency response and post-fire debris flow prediction: a case study from the wildfire event on 20 April 2021 in Mianning, Sichuan, China

Wildfires in forests pose a growing threat to ecosystems, human security and infrastructure. Wildfires can increase surface runoff and erosion processes under short-term intense rainfall, which can transport large amounts of solid material downstream to form debris flows in mountainous areas. To improve the speed of wildfire emergency response and reduce the risk of post-fire debris flows to residents and infrastructure in impacted areas, it is critical to rapidly and accurately identify wildfire dynamics, assess burn severity, and predict debris flows following a wildfire. Based on multi-source data and numerical modeling, we proposed an integrated framework for wildfire emergency response that enables pre-disaster, active-disaster, and post-disaster emergency management. First, we identified the distribution of wildfire rescue elements and wildfire spread dynamics based on high-resolution remote sensing and time-series brightness temperature data. Subsequently, we evaluated the burn severity of the 2021 Mianning wildfire based on the difference in normalized burn ratio (dNBR). Finally, we proposed a susceptibility model to evaluate the occurrence probability of debris flows in the burned mountains, which considered five influence factors: percentage of area with high and moderate severity burns in the catchment, sediment supply length ratio along the main channel, gradient of the main channel, catchment area, and mean slope of the burning zone. Moreover, we predicted the movement processes and hazard ranges of post-fire debris flows under the rainfall scenario of a 100 year return period using the OpenLISEM software. We observed that the total area of the burned area was 11.8 km2, and the high, medium and low burned severity areas accounted for 35.7%, 50.8% and 12.2%, respectively. We predicted that 53.6% of the catchments were characterized as being of moderate or higher debris flow susceptibility. A positive correlation was found between the intensity of post-fire debris flow activity and the burn severity of the catchment.