| The intensification of extreme rainfall caused by climate change and the increase of impervious area caused by urbanization lead to the increase of rainwater runoff,which poses a challenge to the traditional urban drainage system.Low impact development(LID)facilities can effectively control runoff,and have the characteristics of sustainability,flexibility and dispersion,which have been widely studied and applied.Increasing the layout area and the thickness of some structural layers of LID facilities can enhance the runoff reduction effect,but also increase carbon emissions.Only taking runoff reduction as the goal is easy to ignore China's current policy demand for reducing carbon emissions,so it is necessary to coordinate between the two to achieve comprehensive optimization.The performance of lid facilities generally declines under climate change and is likely to face uncertain hydrological risks.It needs to be evaluated under climate change conditions to avoid losses.This paper studies the optimization of runoff and carbon emission control of lid facilities under climate change.Climate change rainfall is designed according to RF(reference period),RCP 4.5(medium carbon emission)and RCP8.5(high carbon emission)scenarios in the rainstorm intensity formula of Guangzhou from 2029 to 2050.According to the characteristics of the study area,rainwater garden,green roof and permeable pavement are selected for scheme design.The runoff reduction effect and carbon emission of the three facilities are calculated by SWMM model of the study area and life cycle assessment(LCA)method by Gabi software.The optimal layout scheme of lid facilities with high runoff reduction rate and low carbon emission under different climate scenarios is obtained by using genetic algorithm coupling objectives,which provides support for decision-makers to select lid facilities according to carbon emission and data reference for the performance of lid facilities under climate change.Through the LCA method,it is calculated that the unit carbon emission of rainwater garden,green roof and permeable pavement is very different.The carbon emission of permeable pavement is about 20 times that of green roof and 2 times that of rainwater garden.The main carbon emission comes from permeable concrete materials;The main carbon emission of rainwater garden and green roof comes from plastic products such as PVC pipe,concave convex drainage board,geotextile and the transportation process of planting soil.Through the optimization algorithm,the layout schemes of lid facilities corresponding to different climate scenarios are calculated.The stronger the climate change is,the higher the carbon emission is.Under the three scenarios,there is an obvious decline in the marginal benefit of "carbon emission-runoff reduction benefit",which is an efficient range when the runoff reduction rate is less than 75%.After that,the increase of carbon emission can only lead to a small increase in runoff reduction rate.By selecting 12 schemes with runoff reduction rates of 60%,65%,70% and 75% respectively under three climate scenarios,it is found that under the same runoff control effect,rcp4.5 requires 19-22% more area than RF scenario and 20-25% more carbon emissions;RCP8.5 scenario needs more than RCP 4.5,the area of lid facilities will be increased by 12-16%,and the carbon emission will be increased by 19-20%.With the aggravation of climate change,the area proportion of permeable pavement in lid facilities is increasing,and the comprehensive benefit is higher under climate change;The rainwater garden has the highest average density among all schemes and is the most important lid facility in the site.It is in RCP8.5.In the scenario of strong climate change,increasing substrate thickness is a more effective choice than increasing area;The runoff capacity of green roof under climate change is relatively limited,the area in each scheme is relatively stable,and the substrate thickness is reduced. |
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