Author(s): H. M. S. M. Herath; A. P. Basnayake; P. R. Sarukkalige; V. T. V. Nguyen
Linked Author(s): Van-Thanh-Van Nguyen
Keywords: Downscaling GEV; Extreme rainfall; Scaling concept; Non central Moments; Runoff modelling
Abstract: Urban stormwater management has been impacted by climate change over recent decades and the challenges will be increased according to the current General Circulation Model (GCM) predictions. This research analyses and compares the possible changes of runoff generation in an urban catchment under current rainfall and future predicted rainfall scenarios. The upper part of the Canning Vale Central Catchment is used as the urban catchment and the catchment is modelled using XPSWMM hydrological and hydraulic model. To evaluate the effect of climate change on the catchment’s rainfall pattern, a spatial and temporal downscaling approach is undertaken. The future precipitation obtained from A2 scenarios of the Hadley Centre Climate Model (Had CM3-A2) and coupled Canadian Global Climate Model (CGCM3-A2), for the periods of 1961–2099 is downscaled both spatially and temporally. The Statistical Downscaling Model (SDSM) is employed in spatial downscaling and the mathematical model, based on the General Extreme Value (GEV) distribution is used in temporal downscaling. Using a frequency analysis of downscaled data, Intensity Frequency Duration (IDF) curves for the future period are developed. The downscaled climate change triggered IDF curves are used as the main rainfall input for the hydrological model. Catchment peak outflow hydrographs are generated for the study area and the results are compared under different climate scenarios. The results show that there is no significant increase of runoff under the Had CM3-A2scenario, and that the peak outflow from the catchment is similar to the current conditions. Results for the CGCM3-A2scenario shows a considerable decrease of runoff generation in the urban catchment in the future. The findings of this study show that even if the behavior of climate change in the future follows any of the scenarios of Had CM3-A2 and CGCM3-A2, the current flood inundation maps can still be used as a guide for the future flood inundation.