Risk Assessment And Scenario Analysis Of Flood Disaster In Chaohu Lake Basin

Geographic Information System (GIS) has provided technical support for multi-criteria decision analysis of flood disaster risk based on its powerful ability of spatial data management and spatial analysis function. However, the current multi-criteria evaluation of flood disaster risk based on GIS lack of consideration of the risk of decision-making, so that it can’t reflect the preference or decision attitude of decision makers, lacking of flexibility and being not beneficial to the comprehensive analysis of various decision-making strategies. In this paper, the ordered weighted averaging (OWA) multi-criteria decision method has been applied to the flood disaster risk assessment in Chaohu basin based on GIS, compensating for the deficiency of traditional flood disaster risk multi-criteria evaluation in multi-criteria decision-making for complex space problem, which can generate more diverse and flexible evaluation results. Main contents have been summarized as follows:(1) Rainfall, terrain, water system, runoff, influence of the Yangtze river, land use, population density, GDP and gross industrial output value have been choosed as evaluation indexes to construct evaluation index system of flood disaster risk in Chaohu lake basin from the view of the mechanism of flood hazard.(2) Various evaluation indicators have been obtained, then been dimensionless and classified with the support of ArcMap9.3.(3) Index weights have been calculated by AHP method and order weights have been calculated by fuzzy quantitative method;(4) Evaluation indexes have been combined with corresponding criterion weights and order weights by the application of OWA module of IDRISI14.0to realize flood disaster risk assessment of Chaohu basin. Than analyse evaluation results under different decision-making risk, and compared them to the result calculated by traditional weighted linear combination. What the results show are as follows:The evaluation results under7kinds of decision risk, more flexible and varied, have been arrived based on OWA-GIS method by changing the decision-making risk coefficients (0.0001,0.0001,0.0001,1,2,10,1000have been choosed). Flood disaster risk levels throughout the whole study area are the highest under the greatest risk of decision-making when α=0, decreasing with the increasing of decision-making risk coefficient a and than being the lowest under the minimum risk of decision-making until a tends to infinity., The evaluation result by OWA method When α=1has turned out to be very similar to the result by traditional WLC method, so that WLC evaluation method can be regarded as one stuation of the OWA multi-criteria evaluation method when α=1. Regions in the southeast plain along the Yangtze River, including the most part of Wuwei, Lujiang and the south of Chaohu, Hanshan, Hexian, experience the highest risk of flood. The conclusion has been verified then by summing up flood occurrences in Chaohu basin over the years.Flood disaster risk situation in the future will change as the influencing factors change since flood disaster system is a dynamical system, while risk scenario analysis technology makes it possible to research the change of flood disaster risk in the future. In this paper, the scenario analysis technology has been applied to realize scenario-driven risk assessment of flood disaster in Chaohu lake basin in the future.Main contents have been summarized as follows:(1) Precipitation, land use, population and economic factors are considered to be main driving factors causing the change of flood disaster risk in the future by the analysis of the mechanism of flood hazard.(2) Thus several disaster scenarios, in which precipitation of30years return period,50years return period and100years return period occur respectively, have been constructed, and than land use, economic and population conditions in2020have been simulated.(3)Annual precipitation of different return periods have been obtained by the use of Pearson-III frequency curve mothed, and CA-Markov model has been applied to predict the land use situation in2020based on existing land use maps of2000,2005and2010, while the population values and GDP values have been forecasted by using simple regression analysis.(4)Annual rainfall, topography, river systems, and the distance from the Yangtze River have been selected as evaluation indexes reflecting flood hazard in2020, while land use types, population density and GDP density being served as assessment indexes of vulnerability.(5) Assessment indexes processing have been down in ArcMap, and weights of assessment indexes have been calculated by AHP. Distribution maps of flood hazard, flood vulnerability and flood disaster risk in cases of occurrence of rainfall of different return years in Chaohu basin in2020are obtained by a weight linear combination of assessment indexes in ArcMap.What the result show are as follows:Southeast plain areas along the Yangtze River face highest flood hazard, that is, these areas are proned to occur flood, while Hefei and Wuwei show higher vulnerability to flood, and areas with the highest comprehensive flood disaster risk all over the study area are the southeast. In addition, flood hazard levels and integrated flood disaster risk levels throughout the region increase as the return period increases, indicating that the greater the precipitation intensity is the higher flood disaster risk is. Throughout results of flood disaster risk assessment in Chaohu lake basin now and in the future, it turns out to be that southeast plain areas along the Yangtze River are the most serious areas among the entire study area facing flood disaster risk either now or in the future. Therefore, the government and policy-making departments should strengthen the work to guard against flood.