Quantitative risk analysis for landslides: the case of the Three Gorges area, China

The purpose of this study was the analysis of life and property risks due to landslides in the Three Gorges area, China. A landslide susceptibility map was created using rough set theory and a support vector machine model. A scenario based on the past landslide frequency and magnitude was used to convert the susceptibility into quantitative hazard maps. The vulnerability was defined quantitatively as a function of landslide intensity and the resistance of at-risk elements. The elements at risk (population, buildings, lifeline engineering, and land resources) were extracted from color aerial photographs, and detailed information regarding these elements was collected via fieldwork. Reconstruction-cost and market-cost approaches were used to estimate the value of property. Quantitative risk maps were developed by integrating the value of the at-risk elements with the vulnerability and landslide hazard datasets. The resulting maps are presented on a continuous scale in which the numerical values indicate the distribution of risk, including the probability of expected economic losses in renminbi (RMB) and loss of lives per map unit for property and residents, respectively. Based on the final risk maps, it is clear that high-risk areas are located in Badong County and other towns and with transportation networks and urbanized areas with dense populations and high property values. Areas of moderate risk were primarily distributed in rural areas and cultivated lands. In addition, the maps show the low-level probability of expected losses in areas where landslide hazard control measures are present or where human activity is sparse, such as unutilized areas and forests. The resulting risk values involve uncertainties and are not precise predictions of future losses, but they may nevertheless help in identifying areas where damage is likely to be greater and where mitigation measures are warranted.