Impacts of climate change on urban rainwater harvesting systems

Rainwater harvesting (RWH) is promoted in many cities (e.g., Beijing and Shenzhen) as a climate change adaptation measure to relieve urban water supply and drainage pressures. In this study, the impacts of future climate change on water saving and stormwater capture performances of RWH systems at cities across four climatic zones of China are investigated. A downscaling technique based on the Climate Generator is evaluated and employed to generate future (2020-2050) daily rainfall data. Performance indices of RWH systems (i.e., water saving efficiency, reliability, and stormwater capture efficiency) calculated using both the future and historical (1985-2015) daily rainfall data are compared. Two water demand scenarios (i.e., lawn irrigation and toilet flushing) are included in the investigation. The water saving performance is positively affected by the increases in future rainfall at the four cities, while the stormwater capture performance is negatively affected as a larger tank size is required to achieve a desired stormwater capture efficiency in the future period. The responses of water saving and stormwater capture performances of RWH systems to climate change are varying with not only the system dimensions (i.e., storage capacity and catchment area), but also the water demand scenarios and locations. RWH systems with larger storage capacity for larger water demand scenarios at humid and semi-humid cities is expected to be more resilient to climate change. The various changing patterns of the performance indices highlight the importance of incorporating climate change in the design of RWH systems. Location-specific adaptive adjustments (e.g., adjusting tank sizes, catchment areas or water demand rates) need to be adopted so that RWH systems can sustainably meet water saving and stormwater control requirements under future climate conditions.