Analysis of the Potential of Rainwater Harvesting by Roofs in Residential Areas in Beijing City
北京市居住区屋面集雨资源的潜力分析

With the rapid development of urbanization in China, traditional water supply systems are facing big challenges. As an old water use technology, rainwater harvesting (RWH) is recognized as one of the most important approaches to addressing increasingly severe urban water issues, thus drawing more and more attentions around the world. In recent years, Beijing City has launched a series of programs to promote the application of rainwater harvesting and sewage water reuse in order to relieve its pressures on water demands. As a consequence, its water supply structures have been improving. However, the research and practice on rainwater harvesting started relatively late in Beijing and rainwater that can be utilized is limited currently. This leads a great deal of rainwater to be discharged as sewage. Comparing with other impervious catchments in a city, roofs are more suitable for rainwater harvesting as there quality is better than other types of rainwater collections. In addition, collected rainwater can be directly utilized for household consumptions in most cases. Quantitative evaluation on the potential of rainwater harvesting from residential roofs can help people better understand the use of urban rainwater and take it as a kind of important water resource. It could also provide meaningful reference for RWH projects in Beijing. After describing three representative modes for rainwater harvesting from roofs and their usefulness, the authors developed a quantitative analysis method to estimate the potential of rainwater harvesting from residential roofs in Beijing. The simulations showed that approximately 216 million m3 water can be collected during the period of 2002-2007 based on the annual rainfall, and 275 million m3 water could be harvested during the same period based on the long-term mean annual rainfall. The total water saving efficiency of household water consumptions can then reach 7.2% and 9.3%, respectively. Based on the further analysis of barriers with regard to the development of unban rainwater harvesting, the authors also estimated the potential of rainwater harvesting from residential roofs under three different scenarios in Beijing by 2020. The outputs indicated that there is a big potential for rainwater harvesting from residential roofs in the city and this is an issue needed to be paid attention. However, there are still a lot of difficulties in applying the technologies to a large scale of practice in Beijing due to the lack of substantial incentives for applications to enhance the rainwater harvesting efficiency. A number of measures were thus put forward to address current problems associated with the rainwater harvesting in Beijing.