Modeling the potential of green roofs and improved green roof systems for urban flood mitigation in Chandigarh, India

Rapid urbanization and increasing rainfall extremes have aggravated urban flooding, which calls for sustainable stormwater management strategies. Green roof systems (GRS) are acknowledged as effective nature-based solutions, yet their hydrological performance under monsoon-dominated conditions has not been well explored. The novelty of this study is in the design and evaluation of an Improved Green Roof System (IGRS) that combines rooftop vegetation with an adjacent infiltration greenbelt to improve stormwater retention and flood mitigation in Indian urban contexts. The hydrological performance of Traditional Roof Surface (TRS), conventional GRS and the proposed IGRS were evaluated for the city of Chandigarh, India using the United States Environmental Protection Agency Storm Water Management Model (SWMM 5.1). For the simulations, we used event-based simulations for 2-, 10-, and 100-year design storms and continuous simulations using daily rainfall data (1974–2024). The GRS showed 42.3%, 33.6%, and 27.3% reductions in runoff compared to the TRS, while the IGRS resulted in higher reductions of 47.0%, 39.9% and 34.7% for the respective design storms. The IGRS also showed improved overall hydrological performance, with the simulated runoff volume decreasing from 610 to 205 m 3 , accompanied by increased infiltration and evapotranspiration, suggesting enhanced stormwater retention. Moreover, the flood volume reduction increased with the width of the infiltration greenbelt, achieving 51% under the largest configuration. The results show that the approach of rooftop greening and ground-level infiltration is a viable nature-based solution to promote urban storm water retention and flood mitigation in monsoon regions The proposed IGRS is a potential adaptation-oriented urban stormwater management solution, but it’s transferability, structural feasibility and performance under anticipated future climate conditions needs to be further explored through field-based investigations.