GIS-based landslide hazard predicting system and its real-time test during a typhoon, Zhejiang Province, Southeast China

Yongjia County, Zhejiang Province, is located in southeast China. Statistics and previous reports have shown that 62% of study area has experienced various forms of slope instabilities, including debris flows and landslides. The geological buildup promotes the occurrence of landslides, since most part of the area is covered by clayey sandstones, volcanic tuffs and other types of pyroclastic rocks. A GIS-based system is established to assess and visualize landslide hazards. The information layers in the MAPGIS system are generated by using 11,397 regular grids with size of 5 mm ∗ 5 mm. At first, Information–Matter-Element Model is adopted to compile landslide susceptibility map by using input parameters such as lithology, structural geology, slope morphology and angle, surface waters and human induced geomorphological changes. Rainfall data, quantity of rainfall and rainfall intensity are obtained to calculate the Effective Rainfall Model. Past landslide frequency with the combination of effective rainfall is used to determine rainfall threshold values and to generate a rainfall threshold map. A warning map is compiled including five-steps of warning levels by overlaying landslide hazard maps and rainfall threshold maps. Above the third level the population is noticed, while at level five immediate evacuation takes place. During “Yunna” typhoon in August 2004, a real-time warning was realized based on the landslide hazard susceptibility map and the real rainfall information. The GIS-based system proved to be satisfactory in predicting areas of landslides, marking nine critical localities during this catastrophic event.