Climate resilience of urban water systems: A case study of sponge cities in China

Resilience is an important aim of climate adaptation in urban development planning. Since 2015, sponge city (SC) pilot projects in China have highlighted the importance of urban water system (UWS), but have paid insufficient attention to extreme and long-term climate change risks. This paper aims to provide a new method for evaluating the urban water system climate resilience (UWSCR), classify China cities in combination with climate hazards, and conduct case studies on SC pilots, proposing ways to improve UWSCR in SCs. Firstly, Taking heavy rain and drought as hazards, an evaluation index system of UWSCR was established, including engineering resilience (ENR), ecological resilience (ECR) and evolutionary resilience (EVR). A combination model based on the analytic hierarchy process (AHP) and entropy weight (EW) method was used to measure UWSCR of 27 SC pilot cities and 253 non-pilot cities at or above the prefecture level in China. Secondly, coordinating Hazard index and UWSCR index, cities are divided into four types. It is found that the ENR and EVR of SC pilots was significantly improved from 2010 to 2020 and are greater than those of non-pilots. Among the four types, Resilient Cities and Low Risk Cities are of high climate resilience (CR) and are mainly distributed in the eastern and central regions of China. High Risk Cities and Vulnerable Cities are of low CR and are mostly distributed in the central and western regions. Among the cities of high CR, SC pilots accounting for 60.7% of the pilot samples, while non-pilot cities only account for 26.5% of the non-pilot samples. Finally, this paper analyzes the typical cases of pilot cities, and puts forward some suggestions, such as considering UWSCR systematically and holistically, improving ECR, making medium and long term adaptation planning and providing differentiated policy support. The originality of this work is to identify four types of cities from the perspective of UWSCR and provide reference for improving CR of SCs.