A rainwater harvesting system in buildings with green roofs and a rooftop greenhouse in Pyongyang

A rainwater harvesting system plays an important role in improving water management and implementing sustainable urban development. This present paper aims to conduct a feasibility study of a rainwater harvesting system in buildings with green roofs and a rooftop greenhouse, while analyzing the runoff coefficient and reliability in the Ryomyong street, Pyongyang, the DPR Korea. The results show that the annual average runoff coefficient of the green roofs accounts for an average of 0.12, while the monthly average runoff coefficients varies in a range of 0(Jan.-Apr., Oct.-Dec.)-0.58(Jul.) in the period of 37 years. With regard to the irrigation of rainwater in the rooftop tank to the greenhouse, the water demand in the period of Dec.-Jun. need to be additionally collected from other sources. When rainwater in the tank under the building is additionally supplied to the greenhouse, the annual average reliability increased from 91% (20 m(3)) to 99% (50 m(3)) according to the increases in the tank volumes. It shows that, when both the rooftop tank 20 m(3) and the tank 50 m(3) under the building are used to the water supply, the demand for the greenhouse could be fully met. Moreover, the results show that, on one hand the annual average reliability is not sensitive to increases in the tank volumes, on the other hand, the increase in catchment surface could substantially lead to improving the reliability of the RWH system. The research findings could assist water management authorities and would be valuable for the local planners and managers in the municipality.