SWMM-Based Hydrological Modelling of Blue-Green Infrastructure for Climate-Resilient Stormwater Management and Urban Flood Reduction in F-North and G-North Wards of Greater Mumbai in India

Indian metropolitan cities such as Mumbai grapple with urbanization, extreme urban density, high built-up areas, loss of green cover, and open spaces, leading to increased impermeable surfaces, urban heat, and flooding occurrences. Modern stormwater management has been characterized as a combination of grey-green approaches. However, the global north benefits from established policies, technical expertise, and funding, enabling large-scale and systematic integration of Blue-Green Infrastructure (BGI) based on district-wide geospatial assessment of BGI systems, in contrast to the global south. Despite this, there remains a dearth of geospatial empirical research from India examining the placement, distribution, performance, and functionality of BGI in integration with existing stormwater management regimes in cities such as Mumbai. Hydrological modelling using tools such as SWMM in the design, planning, and implementation of BGI in Indian cities remains largely unexplored. This study explores the role of BGI strategies in improving urban stormwater management within high-density Indian cities. Using an integrated approach that combines QGIS-based spatial analysis with EPA-SWMM hydrologic-hydraulic modelling, the research examines runoff behaviour, identifies flooding hotspots, and evaluates the effectiveness of Low Impact Development (LID)-based BGI measures—such as permeable pavements, infiltration trenches, and green roofs—applied at the ward level in Mumbai’s F/North and G/North Wards. Detailed land-use classification, spatial mapping, and rainfall simulation (25-year return period) were used to assess pre- and post-intervention conditions. The findings indicate that the applied BGI measures led to a 12.6% reduction in peak runoff (137.6 m³/s to 120.2 m³/s) and a 5.5% decrease in total runoff volume (783,510 m³ to 740,410 m³). More importantly, the flooding volume decreased by 45% (94,111 m³ to 51,707 m³), showing that even modest runoff reductions can substantially reduce flood risk. Less extreme events could see even higher relative reductions or prevent flooding altogether, while also easing downstream hydraulic loads. Overall, strategically placed BGI interventions can significantly reduce surface runoff and peak flow, enhancing stormwater resilience within spatially constrained urban environments. This study provides a replicable, data-driven framework for catchment-scale stormwater planning in dense Indian cities, offering practical insights for policymakers and urban planners to retrofit and adapt existing infrastructure under increasing hydrologic stress and climate variability.