Green roofs for storm water management : a review

The rapid urbanization and industrialization involve an unsustainable use of natural systems, leading to various problems in cities. The urban hydrological system experiences fluctuating amount of surface runoff water when it rains heavily. It has been suggested that green roofs significantly mitigate storm water runoff generation even in tropical climate. Green roofs have become popular due to its proven benefits by mitigating urban heat island effects and protecting biodiversity. The annual rainfall and runoff relationship for green roofs is determined by the depth of the substrate. Water retention capacity mostly depends on substrate’s physical conditions such as dry or wetness. Generally 6 mm to 12 mm rainfall is required for dry substrate to initiate runoff whereas response of wet conditions is mostly straight. Besides, there are some other factors affecting runoff dynamics such as type of a green roof and its slope, age of green roof, type of vegetation, soil moisture characteristics, weather. The review indicates that there is not much research in green roofs performance over storm water runoff; hence there is a need for further research. This paper reviews and addresses the role of green roofs in urban storm water management.