Impact of rainfall properties on the performance of hydrological models for green roofs simulation

Green roofs (GRs) are effective tools for the mitigation of the negative hydrological impact linked to uncontrolled urbanization. Models for runoff response of vegetated covers support planning decisions about the use of this technology in ever-expanding areas, but there is still large uncertainty in this research area. The goal of the present study was to define the accuracy of three selected models for the simulation of the hydrological behavior of a GR, with a particular focus on the precipitation pattern characteristics. The NASH cascade model, SWMM and HYDRUS 1D models were selected. Each model was calibrated over 24 rainfall-runoff events collected at the experimental site located in Southern Italy. Rainfall events were characterized using several criteria and they were divided into convective, stratiform and tropical precipitation types according to the shape of the rainfall profile identified by the rainfall binary shape code. The models returned overall satisfactory performances with average Nash-Sutcliffe Efficiency index of 0.65 for the SWMM and HYDRUS and 0.73 for the NASH model. In general, the models were better performing for stratiform and tropical events. SWMM and HYDRUS were proved to predict with higher accuracy the convective events while the Nash model appeared more suited for stratiform events