Modelling the impact of urbanisation on flood runoff volume

In this study, a relatively simple and intuitive extension to an event-based lumped conceptual rainfall–runoff model, the revitalised flood hydrograph model is introduced and shown to improve model performance on a heavily urbanised catchment. The extension does not affect model performance on a rural catchment. The hydrological losses in the model are calculated based on a percentage runoff type model, initially developed for use in rural catchments and relating losses to soil moisture content, soil moisture capacity and rainfall. By assuming a fixed percentage runoff of 70% from the urban (impervious) parts of the catchment, an overall improvement in predictive ability of the extended urban model is observed on the heavily urbanised catchment. Model performance is generally found to be improved more when considering events occurring with low initial soil moisture content than for events associated with higher initial soil moisture content. A sensitivity analysis indicates that the urban loss-model is relatively robust with regard to percentage runoff and imperviousness of the urban area.