Debris flow susceptibility assessment based on topo-hydrological factors at different unit scales: a case study of Mentougou district, Beijing

Debris flows are a widespread and dangerous geological disaster that cause severe damage to residents, buildings and roads in the Mentougou mountain belt, Beijing. According to existing reports and field investigation results, previous records tend to be of the areas affected by debris flow, not the process area where the debris flow occurred. This study selected eight topo-hydrological factors related to debris flow initiation and hydrological processes to explore the susceptibility of debris flow in the source area. The weights of the factors are determined by the analytic hierarchy process (AHP) and the principal component analysis (PCA) method, and the final evaluation result is calculated based on the information content model (ICM). For different hydrological response units, the evaluation results are quite different. The reason for this is that the information content of topo-hydrological factors varies with the unit size. Based on the verification results of the receiver operating characteristic curve (ROC) and Kappa coefficient, the evaluation model with a hydrological response unit of group A(2) performs better, and nearly half (48%) of the results are with high susceptibility or extremely high susceptibility. Therefore, satisfactory evaluation of the debris flow susceptibility can be achieved based on the application of topo-hydrological factors. The established model is especially suitable for exploring the initiation and migration process of debris flow in Mentougou mountain area and places with similar topography background.