Evaluation of Green Roof Performance in Slowing Down Stormwater Runoff in Urban Catchment, The Case of Samut Prakan, Thailand

Abstract

Urbanization implies a reduction of vegetation leading to an increase of bare lands coverage and the expansion of impervious surfaces. Such circumstances are significantly influence the hydrological cycle, reduce evapotranspiration losses, and accumulate surface runoff, raising the risk of floods, particularly in rapidly developing urban areas. Green roofs are considered as one of the most suitable Green Infrastructure (GI) for densely urbanized areas because they can incorporate into new construction or added to existing buildings during renovation or reroofing without further land consumption. This study aims to evaluate the effectiveness of green roofs in helping to slow down water runoff in response to flood risks in Samut Prakan municipal area. The hydrological model EPASWMM 5.1 was created with rain estimated based on historical data and the green roof installation scenarios. 12 green roof scenarios, consisting of 4 main scenarios, are categorized based on the rainfall events (average extreme rainfall, 10-year return period, 20-year return period, 50-year return period). The simulation results show that green roofs significantly reduce surface runoff and peak flow. Specifically, extensive green roofs in Samut Prakan achieved runoff reduction rates of 14.6% to 54.51%, and peak flow reduction rates of 7.43% to 19.6%. Considering the runoff reduction rate, green roof can provide more hydrological benefit than that of traditional storm management system. While the performance of green roofs in tropical climates may be less effective compared to those in arid and temperate zones, the results of this study are consistent with previous research and provide valuable insights for optimizing green roof design and implementation in tropical country as Thailand.