An FAHP-based Quantitative Method for Risk Assessment of Debris-flow Hazards Using Different Fuzzy Numbers

This paper presents the fuzzy analytic hierarchy process (FAHP) for risk assessment of debris-flow occurrence using three different fuzzy numbers. Three layers are involved in the structure of the FAHP: the goal layer, the criteria layer, and the sub-criteria layer. In the criteria and sub-criteria layers, nine major influence factors are grouped into three categories: (1) topological and geological conditions, which includes the influence factors of slope angle, type of deposit, grain size distribution, and surface plants; (2) watershed conditions, which includes effective watershed area and quantity of outflow of sediment; and (3) rainfall conditions, which includes rainfall intensity, duration, and accumulated rainfall. Judgment regarding the relative influence of these factors is based on a nine-level scale used to form the fuzzy reciprocal judgment matrices for evaluating the weighting vectors for each layer. Two cases of debris-flow disasters that occurred in eastern Taiwan were tested using the FAHP; one was a debris flow, and the other a mudslide. The results showed that the proposed FAHP models using the three kinds of fuzzy numbers as well as the associated influence factors and criteria can successfully predict the risk of debris-flow hazard occurrence. Furthermore, the predicted overall risk indices obtained from the FAHP using the three kinds of fuzzy numbers were smaller than those obtained from AHP, but more practical due to consideration of the uncertainty and vagueness involved in natural hazards.