Impacts of rainfall change on stormwater control and water saving performance of rainwater harvesting systems

Rainwater harvesting is widely implemented to deal with urban water scarcity and stormwater control issues. In the context of climate change, however, the impacts of rainfall change on rainwater harvesting systems (RHS) are still unknown in many regions. In this study, effects of rainfall change on both water saving and stormwater control performance of RHS across six cities in different climatic zones of Pakistan were investigated and location-specific and adaptive measures to mitigate the negative impacts of rainfall change on RHS were proposed. The commonly defined "dry gets drier, wet gets wetter" rainfall change pattern is not retained in the cities. Water saving performance of RHS is positively affected by increasing trend of rainfall at Khanpur and Peshawar, whereas negatively affected by rainfall decreases at Zhob and Murree. Conversely, increasing trend of rainfall is non-beneficial for stormwater control at Khanpur and Peshawar but rainfall decreases are beneficial at Zhob and Murree. Islamabad and Lahore do not have notable changes in performance of RHS due to the non-significant changing trends in rainfall. The impacts of rainfall change on performance of RHS are dependent on not only the trends and extents of local rainfall change, but also tank sizes and water demands. At Khanpur and Murree, the negative impacts of rainfall change on performance of RHS can be resolved by enlarging tank sizes. At Zhob and Peshawar, however, adjusting contributing areas or water demands should also be considered. Therefore, location-specific and adaptive measures should be adopted for RHS to accommodate rainfall change.