Resilience evaluation of sponge city based on relative difference function

Aiming at the comprehensive evaluation of sponge city water system, based on the concept of engineering elasticity, we construct a resilient index system with 17 factors from four dimensions: ecological, engineering, natural and social resilience. Based on the fuzzy variable evaluation model of the relative difference function, the five levels (very strong, strong, medium, weak and very weak) of the resilience thresholds corresponding to the 17 indicators are explained and defined. We take Kaifeng as the research example to evaluate and calculate, and the result shows: the water system resilience classified as Ⅴ in 2013, 2014 and 2015 suggests that Kaifeng water system has a very weak resilience; that as Ⅳ in 2016 and 2017 shows a medium resilience. In addition, the change trend of relative membership coverage of 17 indicators in 2013 and 2017 was analyzed and compared with the construction effect of Kaifeng sponge city, showing that the evaluation results are highly concordant with the actual situation, thus an obvious resilient enhancement process was found. Through the example verification, we have established a reasonable evaluation system and elastic threshold, aiming at the evaluation area of mesoscale, to determine the corresponding relative membership degree through the index information, so as to obtain accurate evaluation results, and provide reliable data support and theoretical basis for the sponge city to improve the resilience of its water system.