Modelling and forecasting of urban flood under changing climate and land use land cover

Chennai is a rapidly urbanizing Indian megacity and experiences flooding frequently. Literature state that climate change and land use change have a significant impact on the runoff generated every year making it essential to study the historical trend and forecast changes in LULC and climate to model runoff. This study considered Adyar watershed for LULC change detection, climate change analysis, and flood forecasting for 2030 and 2050 based on LULC and runoff of 2005 and 2015. A coupled hydrologic–hydraulic model (HEC-HMS and HEC-RAS) was developed to assess flooding for future LULC and climate scenarios. LULC analysis shows an increase in built-up cover by 6%, and climate analysis shows a 74% probability of an increase in precipitation intensity between 2015 and 2050 compared to 2015. It was observed that depth of flooding increased by 19.4% in 2030 and 60.4% in 2050 compared to 2015. This study makes a structural proposition for flood mitigation through flood carrier canals on the downstream reach of the river, which flows through Chennai city. The canals were found to prevent overbanking, thereby providing complete protection against flooding. It is proved that this is the best possible measure that provides the highest flood reduction for the study area.