Evaluation Of Urban Ecosystem Services Excess Demand From The Perspective Of Green Infrastructure

The change of land cover and the concentration of population are two typical characteristics of urbanization,and also the primary causes of the imbalance between supply and demand of urban ecosystem services(ES).In order to cope with the crisis and challenges brought about by urbanization,Green Infrastructure(GI),which provides comprehensive ES benefits,is regarded as an important strategy for sustainable urban development.Compared with the traditional method of relying on ES supply potential for GI planning,it is more practical to identify the ES supply and demand mismatch area as the planning idea of GI site selection priority evaluation.However,the current research of ES supply and demand mismatch mainly focuses on regional,national and even global scales,and lacks relevant research at the city scale.Therefore,it is urgent to quantify and mapping urban-scale ES supply and demand mismatch.After an in-depth analysis of the current research of ES supply and demand mismatch,it is considered that the method proposed by Baro et al.(2015)to evaluate ES excess demand by directly using environmental quality standards is especially applicable to identify the mismatch between ES supply and demand in urban scale.The method has been extended as follows:(1)not only regulation services,but cultural services(the recreation service)are include in this evaluation;(2)introducing a spatially explicit mapping method to map the spatial distribution pattern of ES excess demand in a city scale;(3)improving the quantification methods and indicators from the perspective of environmental disaster risk;(4)utilizing multi-criteria decision analysis method to evaluate the trade-off and synergy of ES excess demand.Finally,this paper proposes a framework of urban ES excess demand assessment from the perspective of GI,and takes the central area of Wuhan as an example to test and demonstrate the framework.First,four ES types were identified,including air purification,stormwater regulation,heat regulation,and recreation services.Then select the appropriate quantitative indicators and excess demand thresholds to quantify and map the individual ES demand.Then ES excess demand trade-off and synergy was analyzed by using Pearson correlation analysis method.And the weight of each ES demand was calculaed by entropy-based weight method.Then we calculated the ES aggregated excess demand based on the weight.Finally,this paper analyzes the correlation between the evaluation results and the current GI ratio to verify the accuracy of the assessment results.In addition,by comparing the evaluation results(2015)with the GI project of Wuhan Central area in 2016,we evaluated whether the GI project matches the ES evaluation results from both the overall and local aspects.The final evaluation results suggest that:(1)There is an excess demand for air purification services in the entire study area,and its spatial distribution has obvious northsouth differentiation characteristics,and the high excess demand areas are mainly concentrated in the northern part of the city.The areas with high flood regulation excess demand are mainly distributed in the areas of Qikou distract,Jianghan distract and Jiang'an distract.The area with high temperature regulation excess demand is mainly concentrated in the urban center,and has a certain gradient distribution trend,that is,the demand decreases from the center to the outside.The area with high recreation services excess demand is mainly located at the edge of the central city,and the demand in the internal central city is low.The weight values of four service demands,such as flood regulation,recreation service,temperature regulation and air purification,are 0.328,0.274,0.269 and 0.129,respectively.The areas with high ES aggregated excess demand values are all concentrated in the Hankou area,mainly at the junction of Qiaokou District and Jianghan District,showing a significant aggregation distribution.(2)There is a significant negative correlation between recreational service and other services,including air purification,flood regulation and temperature regulation,indicating that there is a trade-off between the excess demand for recreation service with the others.Temperature regulation,flood regulation and air purification are positively correlated with each other,and the correlation between flood regulation and air purification is the strongest,and the correlation coefficient reaches 0.634,which indicates that there is a clear synergy between the three ES excess demands.(3)There is a significant negative correlation between the current GI ratio and the ES aggregated excess demand.The correlation coefficient is-0.67 and the significance level is 0.01,indicating the certain accuracy of the evaluation results.The overall evaluation results show that planned GI project is not significantly related to ES aggregated excess demand,temperature regulation,air purification,sa well as flood regulation,and positively related to the recreation service.The local evaluation results indicate that although Hanxing Street does have the highest level of demand for air purification services,but it also completely ignores the high demand for recreation service.This indicates that,regardless of the overall or local view,the current planned GI project in the central area of Wuhan does not match the evaluation results of ES excess demand.Therefore,in order to providing optimal GI site selection and type decision,in the future,a comprehensive GI strategic for a variety of ES demand in Central area of Wuhan is urgent to plan.