Research On Comprehensive Benefits Of Sponge City Construction And Its Monetization Method

To alleviate frequent urban waterlogging,worsening water pollution,and degradation of urban water ecosystems caused by traditional urbanization,China has proposed a rainwater management model suitable for Chinese cities called "Sponge City." The pilot construction of sponge cities began in 2015,and in 2021,the construction of sponge cities was promoted nationwide.The construction results of the pilot cities have shown significant economic,social,and ecological benefits of sponge city development in China.However,there is a lack of quantitative research on the benefits and value of sponge city construction.The indicator system and methods for monetizing these benefits are not sufficiently well-developed,which hampers the progress of comprehensive sponge city construction efforts.Therefore,this study conducted a comparative and systematic research on the comprehensive benefits of sponge city construction and its monetization methods,including identifying the benefits of sponge city construction and improving the evaluation index system for sponge city construction effects.It also developed monetization methods for these benefits and applied them to the planning of Low Impact Development(LID)measures,followed by a case analysis.The research findings can provide theoretical and technical support for the quantitative evaluation of the benefits of sponge city construction and promote the development of sponge cities in China.The main research and achievements of this study are as follows:(1)Identified the benefits of sponge city construction and improved the evaluation index system for the comprehensive effects of sponge city construction.This was done by analyzing the differences between sponge cities and traditional cities in terms of rainwater management at both the city and watershed scales.It analyzed the changes in water resource benefits in various water-use sectors and economic losses due to urban waterlogging in different land-use sectors.The study identified the potential benefits within each sector and constructed a comprehensive benefit evaluation index system for sponge cities.It also constructed a sub-item benefit evaluation index system for sponge cities based on the goals of sponge city construction and the content and indicators of the "Performance Evaluation and Assessment Measures for Sponge City Construction(Trial)" and the "Evaluation Standards for Sponge City Construction."(2)Developed a monetization method called the comprehensive analysis method and applied it to case studies in the pilot areas of the Xixian New Area and Guyuan City sponge city projects.This method considers the overall impact of changes in urban water resources and waterlogging on various sectors.It integrates the identification approach of the comprehensive benefit evaluation system and is based on theories such as "water footprint theory," "water resource shadow price," and the theory of economic losses due to waterlogging.The method comprehensively analyzes and monetizes the ecological,water resource,water environment,and water safety benefits of sponge cities.The calculation results of the case studies show that the benefits in the pilot areas of Xixian New Area range from 10,578 to 13,762 million RMB per year,while in the pilot areas of Guyuan City,the benefits range from 7,814 to 10,205 million RMB per year.The comprehensive analysis method is characterized by simplicity of calculation and a low number of required parameters,making it suitable for quickly estimating the benefits of an entire region.(3)Developed a monetization method called the sub-item aggregation method and applied it to case studies in the pilot areas of the Xixian New Area and Guyuan City sponge city projects,as well as a residential community in Guyuan City.This method is based on the evaluation index system for sub-item benefits of sponge city construction.It uses theories from environmental economics,water economics,and other disciplines to monetize the benefits of each sub-item.The method sums up the benefits of each sub-item to obtain the comprehensive benefits of sponge city construction.The case study results in the pilot areas show that the comprehensive benefits in the Xixian New Area are approximately 88.983 million yuan per year,with ecological benefits,environmental benefits,economic benefits,and social benefits accounting for 25.1%,6.3%,32.9%,and 36.8%of the total benefits,respectively.In the pilot areas of Guyuan City,the comprehensive benefits are approximately 75.116 million yuan per year,with ecological benefits,environmental benefits,economic benefits,and social benefits accounting for 18.2%,2.8%,45.0%,and 33.9%of the total benefits,respectively.The results from the watershed-scale application show that the total runoff control benefits in the Meiyuan Residential Area of Guyuan City are 152,900 RMB/year,with the annual average benefits of each LID facility being 383.3 RMB/bucket for rainwater barrels,73.4 RMB/m2 for sunken green spaces,110.0 RMB/m2 for rain gardens,117.4 RMB/m3 for rainwater ponds,and 17.4 RMB/m2 for permeable pavements.The sub-item aggregation method can be used to evaluate the benefits of sponge city construction at both the city scale and the watershed scale.It requires more parameters and computational work but is suitable for detailed analysis of the composition and proportions of sponge city benefits.(4)Explored the application of the monetization method for sponge city benefits in the planning of LID measures.The benefit-to-cost ratio(i.e.,cost-benefit ratio)was adopted as one of the sub-objectives of the comprehensive goals of sponge city development.By establishing a functional relationship between the deployment ratio of LID measures and the cost-benefit ratio,the monetization method was applied to the planning of LID measures.Taking the pilot area of Guyuan City as an example,a multi-objective optimization function,including the annual runoff control rate,pollution reduction rate,and cost-benefit ratio,was constructed based on the SWMM model and multi-objective optimization theory.Two planning scenarios were set,with Scenario 1 incorporating the cost-benefit ratio function and Scenario 2 incorporating the cost function.By solving the objective function and conducting SWMM simulations,the deployment ratios and effects of LID measures were obtained.A comparison of the two scenarios in terms of engineering construction,runoff control,pollutant reduction,and network overload showed that Scenario 1 outperformed Scenario 2.Therefore,applying the monetization method for sponge city benefits to LID planning helps optimize the deployment of LID measures.