Evaluation of geological hazards susceptibility based on watershed units：A case study of the Changdu City，Tibet

As a natural disaster prone to occur in mountainous areas, geological hazards cause serious economic losses to China every year. In order to reveal the factors influencing of geological hazards susceptibility in typical mountain valley, this paper takes Changdu City as the study area.Firstly, we analyze the spatial distribution of geological hazards, and then divides it into three major watersheds based on the differences of disaster-inducing environments in the study area, selects 10 indicators such as elevation, slope and terrain relief to build a evaluation index system of geological hazard susceptibility , and the weights of index determined based on the Random Forest. The spatial distribution of geological hazards in each watershed of Changdu City is obtained by overlaying with GIS, and it is found that: (1) The types of geological hazards in Changdu City are mainly small disasters, while the distribution of large disasters is relatively small but the hazards are huge and the danger level is high. (2) In general, the factors influencing geological hazards are more or less the same in each basin, but there are still some differences, with the factor of medium altitude and road being more prominent in the Jinsha River basin, the factor of density of settlements being more prominent in the Lancang River basin, and the factor of road being more prominent in the Nujiang River basin.(3) The Jinsha River basin has the largest area of low susceptibility, and the Lancang and Nujiang River basins have the largest area of medium susceptibility; all three basins have the smallest area of high susceptibility, but they are distributed in the whole basin, and mainly in areas with strong human activities and soft lithology.