WILDFIRES AND POST-FIRE DEBRIS FLOWS IN WEST CHINA

Abstract:

Wildfires, common in mountainous regions of the western China, damage riparian farmlands and infrastructures, endanger lives and property, as can the destructive debris flows that often occur in the aftermath of the fires. This study aims to develop an empirical tool to identify and quantify the potential hazards posed by post-fire debris flows in the Sichuan Province, West China. Data in the study watersheds, including soil types and attribute, topology, land use, NDVI, and rainfall intensity have been collected and statistically related to the wildfire indicator, i.e., the differenced normalized burn ratio (dNBR). The results suggest that post-fire debris flows are particularly hazardous since they can exert great impulsive loads, up to three orders of magnitude greater than sediment yields in unburned basin. Besides, we found the rainfall threshold for initiating debris flows has been significantly reduced in burned area. The mechanistic explanations, besides root decay and increase of soil erodibility, also lie in the fact that wildfires potentially result in the increase of overland flow and decrease of the repose angle of vulnerable hillslopes accompanied by the combustion of their organic matter.