Urban floods in Hyderabad, India, under present and future rainfall scenarios: a case study

This study assesses and evaluates the impacts of future extreme rainfall event(s) on conveyance capacity of urban Storm Water Network (SWN) of Hyderabad City, India, along with flood risk analysis and inundation mapping. The catchment runoff volume was simulated using Storm Water Management Model (SWMM). The runoff simulations were carried out for historic and future extreme rainfall event(s). Future rainfall events were simulated under climate change scenarios using Global Climate Model(GCM), GFDL-CM3 of Coupled Model Intercomparison Project Phase 5(CMIP5). Nonlinear regression-based statistical downscaling was used to obtain rainfall at regional scale for Representative Concentration Pathways (RCPs) 2.6, 4.5, 6.0 and 8.5. It was found that RCPs 2.6, 4.5, 6.0 and 8.5 predicted a future extreme rainfall of 693mm, 431mm, 282mm and 564mm for the years 2088, 2098, 2040 and 2068, respectively. SWMM resultsindicated that the future extreme rainfall in Hyderabad can result in increased runoff volumes causing flooding. The existing SWN was capable of handling RCP 6.0 with 82% runoff. However, it was inadequate to convey runoff from RCPs 2.6, 4.5 and 8.5. Modelling results suggest that the conveyance capacity of storm drains can be increased by 25-30% by desilting major drains and outlets.