Runoff Reduction Capabilities and Irrigation Requirements of Green Roofs

In this study, the hydrologic and hydraulic processes occurring in green roofs are analyzed and the similarities and differences in the rainfall-runoff transformation between green roofs and regular catchments are identified. Analytical equations, which can be used to evaluate the long-term average runoff reduction rates, fractions of time when irrigation is needed, and irrigation water requirements of both extensive and intensive green roofs with or without storage layers, are derived by modifying or extending the analytical probabilistic model which was previously developed to model probabilistically the rainfall-runoff processes occurring on regular catchments. The accuracy of these analytical equations is verified by comparing with continuous simulation results. Also demonstrated in this paper are the performances of green roofs with widely different hydrologic designs under arid and humid climate conditions.