Urban flooding management integrating low impact development under climate change scenarios

Urban flooding has been escalating risks in rapidly urbanizing regions, particularly under climate change. This study evaluates flood management strategy in a 297-Ha catchment of Pokhara, Nepal, by integrating Low Impact Development (LID) measures with conventional drainage upgrades under a 25-year design storm. Hydrological and 2D flood modeling in PCSWMM revealed that urbanization and inadequate drainage capacity have caused severe inundation along Lamachaur section, even during relatively frequent 2-year storms. Climate projections indicated no major increase in extreme rainfall depth but a higher frequency of intense events, highlighting increasing flood exposure. Implementation of LID strategies including permeable pavements, bioretention cells, and green roofs reduced total runoff by up to 67% and peak flows in several sub-catchments by more than 40%, demonstrating the effectiveness of decentralized, nature-based solutions. A combined approach of LID with upgraded drainage improved performance even with less LID measures, lowering total runoff by around 20%, reducing peak discharge, and significantly minimizing junction flooding. The study’s novelty lies in applying an integrated LID-structural framework under climate change in a Himalayan urban context, where such approaches often remain underexplored. These results provide clear, actionable guidance for sustainable flood risk management in data-scarce, rapidly growing cities.