A GIS Based Regional Torrent Risk Zonation
基于GIS的山洪灾害风险区划

This paper explores the methodology for compiling the torrent hazard and risk zonation map by means of GIS technique for the Red River basin in Yunnan province of China, where is vulnerable to torrent floods. Based on a 1:250,000 scale digital map, six factors including the number slope angle, rainstorm days, buffer of river channels, maximum runoff discharge of standard area, debris flow distribution density and flood disaster history were analyzed and superimposed to create the torrent hazard risk evaluation map. Population density, farmland percentage, house property, and GDP as indexes accounting for torrent hazards were analyzed in terms of vulnerability mapping. Torrent risk zonation by means of GIS automatically was overlaid on the two data layers of hazard and vulnerability. Then each grid unit with a resolution of 500 m × 500 m was divided into four categories of the risk: extremely high, high, medium and low. Finally the same level risk was combined into a confirmed zone, which represents torrent risk of the study area. The risk evaluation result in the upper Red River basin shows that the extremely high risk area takes up 17.9% of the total inundated area of 13 150 km2, the high risk area is 45.9% of 33 783 km2, the medium is 25.2% of 18 563 km2 and the low risk is 11.0% of 8115 km2.