Uncertainty analysis on zonation maps of debris flow hazard in Yunnan Province, China

Different researchers select different factors and use different methods to assess the regional hazard degrees of debris flow. Consequently, even for the same region, there are often different hazard zonation maps, and there must be some uncertainty in the zonations. Thus the certainty analysis of zonation maps becomes obviously important. For debris flow hazard, those zonation maps with a certainty analysis could provide most valuable information for land users, hazard managers and policy makers. By comparison of three researchers’ findings in Yunnan Province, this paper shows that seven to nine influential factors are chosen for the zonation maps. Spatial density of debris flow ravines, regional average rock-weathering coefficient, yearly precipitation, days of ≥ 50 mm daily rainfall, and proportion of sloping land with slope ≥ 25° to the total land are the most acceptable factors. Mathematical methods of maximum-minimum values, upper-lower limit values and Fuzzy values are used to quantify the factors. Step-by-step methodology is commonly used for the zonation maps. Research results show that maximum uncertainty is 66.6% and minimum uncertainty is 35.7% in debris flow hazard maps of Zhaotong Prefecture and Yunnan Province. Therefore there is still much work for us to improve the zonation methodology. Foundation item: Supported by the Education Bureau of the Chinese Academy of Sciences. Biography: LIU Xi-lin (1963–), male, a native of Hunan Province, is a research professor. His research interests include debris flow assessment and geomorphology.