A water balance approach to assess rainwater availability potential in urban areas: the case of Beijing, China

Rainwater is an underutilized water resource that has become more important in recent years; due to severe water logging and water shortage in cities. The evaluation of rainwater harvesting potential is of fundamental importance in planning rainwater harvesting systems and management policies. In this study, we used minute-interval rainfall data and the water mass balance method coupling urban hydrological processes to assess the annual rainwater availability potential (RAP) of different underlying surfaces in the urban areas of Beijing (inside the 5th Ring Road). The estimated total RAP was 154.49 million m³ in 2013. About 53% of rainwater could be effectively harvested for use, among which the rooftops had the highest harvesting ratio of 70%, and contributed about half of the total RAP. Indirect use of rainwater can be achieved through infiltration facilities, of which concave green land construction and porous brick pavement can increase the amount of rainfall that infiltrates into the soil by 18.89% and 55.69%, respectively. Rainwater harvesting and utilization could serve as a significant water source for the urban areas in Beijing.