Construction and application of sponge city resilience evaluation system: A case study in Xi 'an, China

Abstract

Urban vulnerability is evident when highly complex flood risks overlap with diverse cities, and it is important to enhance the resilience of cities to flood shocks. In this study, a sponge city resilience assessment system is established considering engineering, environmental and social indicators, and the grey relational analysis method(GRA) is used to quantify sponge city resilience. At the same time, a multi-objective optimization model is established based on the three dimensions of water ecological environment, drainage safety, and waterlogging safety. The optimal configuration of grey-green infrastructure is weighed by combining the ideal point method, aiming to ensure that cities effectively reduce flood risk through the optimal configuration scheme. Taking the Xiaozhai area in Xi'an as the study area, the evaluation results show that the grey relational degree(GRD)of the resilience indexes of the original scheme is between 0.390–0.661 under the seven different return periods. While the optimization scheme ranges from 0.648–0.765, with the best sponge city resilience at a return period of 2a. Compared with the original scheme, the optimized sponge city resilience level increases from level II to nearly level I under the low return period and from level IV to level II in the high return period, indicating that city's ability to cope with waterlogging and pollution is enhanced significantly. Besides, the main factor affecting the sponge city resilience is the runoff control rate, followed by pollutant load reduction rate, which can provide a methodological framework for the assessment and improvement of sponge city resilience.

Research on the problems and strategies of sponge city construction in China

“…According to the Jiaozuo Sponge City Standard Construction Three-Year Implementation Plan, the sponge city construction of Jiaozuo involves 151 projects in 7 categories, with a total investment of 4.233 billion yuan. After the sponge city was built, according to the water quality test results, the water quality of the original 10 black and smelly water bodies in Jiancheng District of Jiaozuo City basically reached the standard after treatment, and there was no black and smelly water [11]. Moreover, the public opinion poll showed that the surrounding residents were satisfied with the water bodies' treatment outcomes, and there was no event that led to a complaint being filed.…”

“…Moreover, the public opinion poll showed that the surrounding residents were satisfied with the water bodies' treatment outcomes, and there was no event that led to a complaint being filed. There has been varied degrees of improvement in each of the four areas of water ecology, water resources, water environment, and water security [11].…”

“…Under the guidance of national policies, the academic circle has gradually shifted the focus of sponge city research from concept and connotation to method system, providing the groundwork for the development of a rigorous and effective evaluation methodology for the effect of sponge city construction. The sponge city evaluation model constructed by many scholars covers environmental performance, market demand, public participation and other aspects, which can reflect the key issues of sponge city project construction in a more comprehensive way [11]. Meanwhile, residents say that sponge cities are of great help in reducing urban floods and easing traffic [12].…”

“…For planning new areas, the idea of building sponge cities should be implemented in the planning stage, and the original rivers, lakes, wetlands, pits and so on should be protected to the maximum extent. On this basis, the total annual runoff control rate is taken as a control index for construction, to give great consideration to the rain's ability to absorb, hold, and slowly release water by low-impact development facilities, and to lessen the negative effects of construction and urban development on the environment [11].…”

“…Figure 2. The regional distribution[11]. According to the Ministry of Housing and Urban-Rural Development, sponge cities should cover at least 20 percent of China's urbanized areas by 2020, and at least 80 percent by 2030.…”