LAUSR

Abstract Reduction in runoff and increase in actual evapotranspiration (AET) are two well-known benefits of green roofs. However, few studies have been carried out to investigate how green roofs affect runoff and AET when there is interaction between them. Such interaction is most prominent when green roofs have an additional storage layer. In this study, a modified hydrological model for green roofs is proposed to explicitly describe water retention and release in different layers and during wet/dry periods, which can reflect the interaction between runoff and AET under alternating dry and wet conditions. After calibration and validation with experimental data, the model was used to evaluate the combined effects of runoff reduction and increase in AET for green roofs under moist sub-tropical weather condition (such as Shenzhen, China). The results indicate that the daily AET and event runoff of green roofs decrease with increasing antecedent dry period (ADP); an additional storage layer can increase the ability of green roofs in reducing runoff and increasing AET. Generally, the effect is more pronounce under weather conditions with higher temperature, more rainfall amount and longer ADP. Such results provide hydrologists and engineers with a new and effective tool to simulate and understand the performance of green roofs by considering water retention and release in the layers.