Changing Flood Risk in an Urbanizing Landscape: A Study from Patna, Bihar, India

Changing Flood Risk in an Urbanizing Landscape: A Study from Patna, Bihar, India Vishal Kumar* Rapid urbanization has significantly transformed land-use patterns, altered the hydrological behaviour of many Indian cities, and intensified their exposure to flooding. This study examines how flood dynamics and urban expansion have co-evolved within the Patna metropolitan area between 2016 and 2024. Multi-temporal Synthetic Aperture Radar (SAR) imagery was analysed to map flood inundation for major flood years between 2015 and 2024, and time-series geospatial analysis was used to identify spatial shifts in flood hotspot zones. In parallel, built-up area growth was mapped using Sentinel satellite data classified through a Support Vector Machine (SVM) approach, which efficiently distinguishes impervious surfaces from vegetation and open spaces. Comparative analysis of the flood layers and urban expansion patterns reveals that rapid, and often unregulated, development has progressively encroached on natural drainage paths and floodplains. The results indicate a marked rise in flood exposure across low-lying areas, especially along the Ganga River corridor. The findings emphasise the urgent need to integrate land-use regulation, floodplain zoning, and nature-based drainage solutions into Patna's urban planning process. Overall, the study offers a transferable framework for sustainable urban management in Patna and comparable riverine cities across India. * Department of Geography, Central University of South Bihar, Gaya, India, Email: [email protected]