Application of a Flood Risk Assessment Model Combining Analytic Hierarchy Process Modified by Trapezoidal Fuzzy Number and Variable Fuzzy Set Theory: A Case Study in Zhejiang Province, China.

The scientific evaluation of regional flood risk is particularly important for flood management. Past studies build a hierarchy evaluation index system with two factors and ten sub-factors to assess flood hazard risk, each factor contains five sub-factors. The weights of the sub-factors in their respective evaluation systems are (0.065, 0.129, 0.210, 0.215, 0.378) and (0.399, 0.152, 0.155, 0.180, 0.109) respectively, from expert scoring results optimized by Analytic Hierarchy Process (AHP) modified by Trapezoidal Fuzzy Number (TFN). Variable Fuzzy Set Theory (VFST) is adopted to calculate the risk values of the two factors, the weighted average of two factors risk values is used as flood disaster risk value. Based on above steps, a flood disaster evaluation model is established and applied to evaluate regional flood risks in Zhejiang Province. Extremely low risk, low risk, moderate risk, high risk, extremely high risk areas are 51017 km2,10090 km2,10112 km2,13428 km2 and 19153 km2, respectively occupy with 49.15%, 9.72%, 9.74%, 12.94%, and 18.45% of study region. TFN-modified AHP calculates the weights of sub-factors, considering the subjective cognition of experts and the objective response of factors, which makes the results more representative and scientific. Application of VFST decreases the randomness and uncertainty of flood risk assessment, which improves the stability of evaluation process and reliability of evaluation results. Meanwhile, 30×30m basic evaluation unit adopted in this study accurately and objectively represent the spatial distribution of flood hazard in Zhejiang Province, China. The evaluation results of the model are validated to be consistent with the actual situation of flood disaster.

A Novel Method in Surface Water Quality Assessment Based on Improved Variable Fuzzy Set Pair Analysis

In the case of surface water pollution, it is important and necessary to accurately assess the level of contaminated water and ensure the safety of drinking water for people in disaster areas during floods. However, for the assessment of the strict requirements of drinking water, traditional assessment methods still have some limitations, such as low precision and rationality. In order to overcome these limitations, in the light of the theory of set pair analysis and variable fuzzy set, we propose an improved variable fuzzy set pair analysis method (IVFSPA), which combines the analysis framework of variable fuzzy set and set pair analysis, and has made some improvements to the fusion architecture. Firstly, we present a novel game theory comprehensive weighting method, in which the objective entropy method and the subjective analytic hierarchy process(AHP) method employed to obtain the reasonable weight. Then, based on the Nemerow index method, we improve the arithmetic form of “ P i ” (Equation P) to replace the fuzzy comprehensive evaluation method. Furthermore, we design a double judgment mode of combining the principle of maximum membership degree with the positive and negative relationship between the standard value and the measured value, which can accurately judge the evaluation level of surface water quality. Finally, to validate and verify the effectiveness of the proposed method, experiments was conducted at the representative river collection sections of Nanking, China, employing water quality data of 14 sampling sections in their rivers in Nanking during the 2017 flood. In terms of performance metcrics of precision and rationality, based on the values of “TP”, “NH3-N”, “Pb”, “AS” and “KMnO4” of “Ch-lh section/Chuhe gate” are 0.415, 3.77, 0.07, 0.23 and 7.12, respectively, the level of Ch-lh section/Chuhe gate is that the IVFSPA is Class V and the rest are class IV. Results of experiments show that our IVFSPA method can achieve a good performance, compared with other traditional methods.