Assessing climate change impacts on the reliability of rainwater harvesting systems

Rainwater harvesting (RWH) systems recycle runoff, increasing the sustainability of water supplies; they may also reduce runoff discharges, and thus help meet water quality objectives. RWH systems receive runoff and thus will likely be impacted by changes in rainfall induced by climate change (CC). In this paper, we assess CC impacts on RWH with respect to the reliability of water supply, defined as the proportion of demands that are met; and the reliability of runoff capture, defined as the amount stored and reused, but not spilled. Hypothetical RWH systems with varying storage, rooftop catchments, irrigated areas, and indoor water demand for 17 locations across the U.S. were simulated for historical (1971-1998) and future (2041-2068) periods using downscaled climate model data assuming future medium-high greenhouse gas emissions. The largest change in runoff capture reliability would occur in Chicago (12.4%) and Los Angeles (+12.3%), respectively. The largest change in water supply reliability would occur in Miami (+22%) and Los Angeles (-17.9%), respectively. The effectiveness of RWH systems for runoff capture is likely to be reduced in the eastern, northwestern, and southeastern U.S. Conversely, for most locations in the western, southern, and central U.S., RWH systems are expected to become less effective for water supply purposes. The additional storage needed to compensate for these reductions in water supply and/or runoff capture benefits was estimated. The results of this study can be used to design more resilient RWH systems with respect to CC, and thus maximize the dual objectives of RWH.