Abstract <p>Over the past decades, urban flood risk has increased dramatically due to growing flood hazards and asset exposure. Flood-related losses are greater in developing nations’ cities characterized by high population density and overstressed stormwater drainage systems. While Low Impact Development practices (LIDs) have been successful in reducing floods in developed countries, their implementation in developing nations is challenged by spatial constraints due to randomly expanding urban clusters. This study evaluates rain gardens’ effectiveness in mitigating flood risk in the Barapullah basin of the National Capital Territory (NCT) of Delhi by selecting suitable implementation areas and subsequently analyzing alterations in runoff characteristics. Rain gardens can efficiently reduce the catchment discharge by ~39%, 30%, and 22% for 2-year, 5-year, and 10-year return periods, respectively. Further, an urban flood risk index is used to distinguish hazard from risk and evaluate the efficiency of rain gardens in reducing flood risk under varying built-up scenarios. The findings of this study are expected to aid policymakers and urban planners in prioritizing urban flood risk mitigation efforts.</p> Highlights <p><UnorderedList Mark="Bullet"> <ItemContent> <p>A limited implementation of rain gardens can significantly reduce flood discharge.</p> </ItemContent> <ItemContent> <p>Rain gardens implemented upstream can reduce flood risk downstream.</p> </ItemContent> <ItemContent> <p>Rain gardens can mitigate future urban flood risk in highly urbanized catchments.</p> </ItemContent> </UnorderedList></p>