Evaluating Green Roof Stormwater Regulation

With the rapid development of urbanization construction in China,the original natural ecological spaces within the urban areas are decreasing while urban impervious surfaces are increasing.The original natural drainage system and water circulation system has been destroyed,leading to increase the risk of flooding in the city.This not only brings the double hidden dangers of life and property to urban residents,but also seriously hinders the healthy development of the city.As an important method in the new urban stormwater management solution,the green roof plays an important role in the increase of urban green space and permeable surface area,mitigating the risk from flood disasters effectively.Therefore,quantitative analysis of the stormwater regulation effect and cost-effective of the green roof on the building scale and basin scale is of great significance,it can provide a basis and reference for the planning and construction of the sponge city.This study takes the real green roof of Jinling Primary School and the Jiuxiang River sub-basin as the study area.High-precision observation instruments are used to observe the rainfall and runoff data for a long time.Through long-term observation,the runoff control capability of the green roof was analyzed at first,and the main influencing factors were identified.Secondly,the cost-effectiveness of the green roof in the 30-year life cycle was evaluated.At the basin scale,this study first evaluated the potential of the building houses in the study area according to the green roof construction criteria,and verified the SWMM model based on the measured runoff;Then,based on the SWMM model,the stormwater regulation ability and its variation characteristics of the green roof in three different construction scenarios(status S0,50%roof greening scenario S1,100%roof greening scenario S2)and three different distribution patterns(actual distribution pattern L0,near watershed outlet distribution pattern L1,away from the watershed outlet distribution pattern L2)were simulated under different rainfall scenarios.Finally,the stormwater regulation benefits of green roofs under different scenarios were evaluated,the results are expected to provide decision-making reference for the promotion and popularization of green roof in urban areas.The main conclusions of this study are as follows:1)Analysis of the stormwater regulation ability of green roof at the building scale shows:a)The green roof at the building scale shows good stormwater regulation ability.The range of runoff control ability varies greatly in different rainfall events.Decision tree classification results show that the main factors affecting the retention ability of green roof are total rainfall,rainfall intensity and growth substrate soil water content.b)From the perspective of runoff reduction,the cost efficiency and return on investment ratio of the green roof in the 30-year life cycle are 12.98 yuan/m3 and 5/12(0.41),respectively.This proves the construction potential and value of the green roof.2)The construction potential and the analysis of the stormwater regulation ability of green roof at the basin scale show that:a)The green roof construction potential in the study area is relatively high.The total area of green roof suitable for construction is 27.49ha,accounting for 64.99%of the total roof area of the building.b)The difference in green roof construction area and spatial distribution pattern on the basin scale has a significant impact on stormwater regulation capacity.In terms of four rainfalls,the green roof stormwater regulation ability in the construction scenario S2 is better than the construction scenario S1,and both are better than the current situation S0;The distribution pattern L0 and the distribution pattern L1 have similar stormwater regulation effects,and both are better than the distribution pattern L2.When the retention capacity of the green roof is limited for rainfall characteristics,the green roof construction area becomes the main factor affecting the ability of the runoff control.The increase in construction area of green roofs can significantly improve the stormwater regulation capacity.c)The cost efficiency and return of investment of green roofs under different construction scenarios and distribution patterns on the basin scale are significantly different.The cost efficiency(14.40 yuan/m3)and cost-effectiveness ratio(0.49)of construction scenario S2 is better than the cost efficiency(25.55)and cost-effectiveness ratio(1.38)of construction scenario S1;the cost-effectiveness of distribution pattern L0 and L1 is close,and two Both are far superior to the distribution pattern L2.Based on the long-term observation data and SWMM model,this study demonstrates the ability of green roof to control runoff on the building scale.It reveals the main influencing factors affecting the ability of green roof runoff control and evaluates the cost-effectiveness of green roof on the building scale.On this basis,Based on the runoff observation data and the aerial image data of the drone,the verification of the SWMM model and the potential evaluation of the green roof construction were completed.Then based on the SWMM model,the stormwater control ability and its variation characteristics of the green roof at the basin scale are analyzed under three different construction scenarios and distribution patterns.Finally,the cost-effectiveness of green roof construction on the basin scale is analyzed.This study is expected to provide decision-making basis for the construction of sponge cities.