Socio-economic And Environmental Evaluation Of Green Versus Grey Infrastructure

Green infrastructure(GI)emerges as a holistic stormwater management strategy,which can offer multispectral benefits as well.Strong proof of project success can help make green infrastructure appeal more efficient for various sectors and open up the door to a range of broad opportunities.However,it is difficult to thoroughly evaluate the performance of such natural systems.Green roofs,bioretention and permeable pavements reduce water,grey infrastructure and energy consumption costs and therefore generate economic benefits.Also providing climate change and air pollution reduction benefits,and they also bring social benefits,such as improving lifestyle,urban greenery,and improving public health and education.This study creates a framework to quantify life cycle values for the socio-economic and environmental benefits as well as for the benefit of the green infrastructure net life cycle.In order to provide more dynamic assessment,this research covers more than single aspect of cost-effectiveness;capital costs,operation and maintenance costs and life cycle analysis of green infrastructure vs conventional practices.Although quantification and valuation methods are limited for bioretention systems,especially for permeable pavement.Due to their complex nature and less scientific researches published on benefit quantification and the scarcity of data are two main reasons of such limitations but these two green infrastructure practices cannot be left out since they are widely applied for bio infiltration,water quality,runoff reduction and habitat improvement.In this Research,Yuelai district in Chongqing is selected as case study.The 25-year environmental and economic benefits of overall GI project are 0.161 million RMB and0.156 million RMB respectively.The social benefits are 996.267 million RMB based on1%private willingness-to-pay,Public willingness-to-pay 198.841 RMB and an average of 4223 domestically owned transactions.Subtracting the 25-year present value of cost from the present value of benefits at an inflation rate of 2.28%and discount rate of 4.35%,the net benefits are 47.382 million RMB or an annual unit value of 1.931 RMB/m~2.The unit cost of green roofs,bioretention systems,and permeable pavements 300 RMB/m~2,520 RMB/m~2 and 300 RMB/m~2 respectively,and the 25-year operation and maintenance cost of 109 RMB/m~2,252 RMB/m~2 and 304 RMB/m~2 respectively.Permeable pavement,green roof and bioretention system contribution in total present value costs is 99.84%,0.145%and 0.015%respectively.Overall,the survey offers a framework in which green infrastructure practices quantify and evaluate the cost and benefits of their life cycles.The framework in the context can be changed on the basis of local information and used worldwide in many other cities.