Modelling of Green and Grey Roofs in Cold Climates Using EPA’s Storm Water Management Model

Rooftops retrofitting, typically extensive green roofs, is a favoured sustainable drainage system technology in densely developed urban areas. They provide multiple benefits in terms of stormwater retention and runoff detention. The latest version of Storm Water Management Model (SWMM) 5.1.012 with Low Impact Development (LID) Controls was used to model hydrological the performance of a green and grey (non-vegetated) roof by defining the physical parameters of individual layers in LID Control editor. In this study, high-resolution 1-min data from a previously monitored green and grey roof were used to calibrate the SWMM LID Green Roof module. Results from the un-calibrated model were unsatisfactory considering the hydrological response of the green and grey roof. After calibration, the observed and simulated runoff had Nash-Sutcliffe model efficiency (NSME) of 0.88 (green roof) 0.68 (grey roof). This indicates that better fit between observed and modelled runoff could be achieved with calibration, primarily of the grey roof. Ideally the calibrated parameter set of the LID modules should be transferable between watersheds given the same LID structural build up. This should be investigated through further research finding the optimal parameter set, and data validation of proposed parameters across catchments.