Evaluation of urban flood resilience and its Space-Time Evolution: A case study of Zhejiang Province, China

Urban floods have become increasingly frequent in recent years, highlighting the need for resilience evaluation and the identification of strategies to improve urban flood resilience. In this study, a system of resilience evaluation indicators is proposed to quantitatively evaluate the level of urban flood resilience. The entropy method used to calculate the resilience index and the space–time permutation scan method used to analyze the space–time aggregation characteristics of urban resilience levels are combined to establish a methodology for evaluating urban flood resilience. An evaluation indicator system for urban flood resilience is proposed, encompassing aspects of natural, economy, society, and infrastructure. This system attuned to the local needs of urban flood resilience evaluation, tests the applicability of the Guide for Safety Resilient City Evaluation (GB/T 40947–2021) in this study. Moreover, it incorporates key common indicators extracted from prior studies on urban flood resilience evaluation. Zhejiang Province, a flood-prone area in China, is selected as the study area, and the proposed evaluation indicator system is used to evaluate the urban flood resilience levels in Zhejiang and their space–time trends from 2011 to 2020. The results show that resilience levels have improved in the natural, economic, and infrastructure aspects, while the resilience levels of social aspect remain high. From 2011 to 2014, two distinct aggregation patterns emerged, delineated as inland-type and coastal-type aggregation areas. An analysis of both patterns was conducted, considering an array of influencing indicators, such as green coverage rate in built-up areas, population age structure index, gross domestic product, density of resident population in built-up areas, and per capita disposable income. The period from 2014 to 2020, however, did not reveal any significant aggregation characteristics. This study provides a reference for establishing an urban flood resilience evaluation indicator system and an in-depth understanding of urban flood resilience, and targeted recommendations to bolster urban flood resilience in the study area.