Susceptibility zoning of different types of mountain torrent disasters in the Yangtze River Basin of sourthern China

The Yangtze River Basin has become the most intensive area of mountain torrent disasters in China because of its complex geological topography and climatic conditions. Susceptibility zoning of the mountain torrent disasters is of significance to the integrated disaster prevention system. The study on the susceptibility of mountain torrent disasters in view of the large-scale(inter-provincial) region of the Yangtze River Basin can provide scientific basis for the study of planning, deployment and implementation of mountain torrent disaster prevention in the Yangtze River Basin and similar areas. The assessment indices were established for the susceptibility evaluation of three kinds of mountain torrent disasters in the Yangtze River Basin, based on the affecting mechanism of natural geographical factors on the formation of the mountain torrent with county as assessment unit. The susceptible indicators for three kinds of mountain torrent disasters were calculated based on the method of analytic hierarchy process (AHP) using Matlab. The Yangtze River Basin was classified into four susceptibility degrees of areas for three kinds of the mountain torrent disasters, i.e. highly-susceptible area, medium-susceptible area, lowly-susceptible area and insusceptible area, using classification scheme by ArcGIS natural spacing. The river flood disaster showed a tendency to decrease gradually from east to west, and centered in the middle and eastern basin. The highly-susceptible area of landslide disaster is mainly in the middle of the basin and certain areas like northern Yunnan and the mountains of Longnan, southern Gansu in the upstream of the river, with the most concentrated area in the east of Sichuan Basin. The highly-susceptible area of debris flow disaster is mainly in the west of the basin, and happened most frequently on fault zones in the first and second ladder transition districts. The results showed obvious differences in the distribution of different mountain torrent disasters in the basin. Over 80% of historical disasters were located in the assessed highly-susceptibility area for all three types of mountain torrent disasters. The assessment results can well indicate the regional distributions of different types of mountain torrents.