A study on harvesting rainwater by applying green roof

Rapid urban growth, poor drainage, and climate-induced heavy rainfall have led to frequent urban flooding. Green roofs, as a form of Low Impact Development (LID), provide a sustainable option to mitigate surface runoff and enhance urban resilience. This study evaluates the potential of green roofs in Chattogram City using the Storm Water Management Model (SWMM) with ten years of rainfall data (2013–2022) and geospatial inputs processed through Google Earth Engine (GEE) and Geographic Information System (GIS). Rooftop areas of 6,584 buildings were classified following Bangladesh National Building Code (BNBC) 2020 to simulate four types of green roof configurations, supported by 2D and 3D visualization for spatial planning. Model calibration and validation ensured reliability, with runoff coefficients aligned with earlier studies. Results indicate that green roofs can significantly reduce surface runoff, with an annual reduction of 752,800 m³, while also delaying peak flows. A sensitivity analysis further confirmed that storage-related parameters, particularly soil thickness and field capacity, exert the greatest influence on runoff reduction outcomes. In addition to flood mitigation, green roofs demonstrate co-benefits including urban cooling, biodiversity enhancement, and water reuse potential. The findings highlight the scope of integrating green infrastructure into urban planning and emphasize the importance of enabling policies, particularly the incorporation of green roofs into the BNBC, to promote climate-resilient development in rapidly urbanizing cities. • Green roofs reduced stormwater runoff in Chattogram by up to 88% (mean 68.4%). • SWMM modeling with 10 years of rainfall data confirmed hydrological performance. • Soil depth and field capacity were the most sensitive parameters influencing results. • Green roofs provide co-benefits: water reuse, biodiversity support, and urban cooling. • Results support integration of green roofs into BNBC as a climate adaptation strategy.