Green roof as flood mitigation in Ghana

Rapid urbanization in cities has increased impervious ground cover, leading to greater flood risks due to reduced natural infiltration. Sunyani Municipality in Ghana, once known as the cleanest city in the country, is currently grappling with challenges related to improper city planning and development, resulting in unprecedented flooding. The conversion of green spaces into impermeable surfaces has exacerbated these flood hazards. Despite governmental efforts to address the issue through various stormwater management strategies and interventions, such as drainage systems and solid waste management, flooding remains a persistent challenge. However, Green/vegetative roofs represent sustainable solutions that offer multiple benefits, including stormwater management and potential flood mitigation. Despite these benefits, it is largely unexplored in Sunyani City. This study explores the implementation of green roofs as viable stormwater mitigation controls for the city in response to runoff and flood threats. The study employed a green roof potential assessment method within the Environmental Protection Agency Storm Water Management Model (EPA SWMM). Hydrology and hydraulic parameters were determined and dimensioned before being used to model the situation in Sunyani. The results showed that green roofs can reduce surface runoff from 90% to as low as 40%, while retaining up to 60% of precipitation. These findings affirm the viability of green roofs as effective urban flood mitigation tools, offering co-benefits such as urban cooling and water reuse. The study provides practical recommendations for integrating green roofs into local planning policies, encouraging uptake among stakeholders and supporting climate resilience goals.