Flood risk reduction in a river basin under climate change

Abstract

A flood and its occurrence is a complex interaction between environmental, socio- economic and physical factors. climate change is an imminent witness of extreme events occurring more frequently and floods have emerged as one of the pressing challenges in our society. The current research study strives to simulate extreme streamflow on a daily time scale by adopting hydrologic and hydraulic modeling in order to assess the flood risk in a changing climate. This research was applied to the lower Pennaiyar and Gadilam sub-basins located in the state North eastern side of Tamil Nadu state, India. The efficiency of the HEC-HMS model was precisely examined for each flood events during calibration (2015, 2017, 2018, 2020, and 2023) and validation (2015, 2018, and 2020) stages using the coefficient of determination R². The R² and NSE values for the three major flood event 2015, 2018 and 2020 are found to be 0.88, 0.83, 0.86 and 0.85, 0.8, 0.82 respectively. The R² and NSE values in the results reveal that the calibrated model performs well in the validation. The EC-EARTH 3 climate model of CMIP6 under the SSP2-4.5 and SSP5-8.5 scenarios is employed for future flood simulations. The EC-EARTH 3 GCM data was utilized to generate hydrographs pertaining to different return periods. The hydraulic modeling through the HEC-RAS 2D model enabled the development of flood inundation maps for future SSP scenarios under 25, 50, 100 year return periods. An integrated approach of combining hydrologic and hydraulic modeling with risk reduction strategies using the HEC-RAS terrain modification tool was adopted in this study. The flood estimates are used as the basis for the planning and implementation of suitable flood control measures and flood water conservation structures. The results revealed in this research provide valuable insight for decision-makers.