When considering the percentage changes of the rainfall for the next century, five out of six model results show a positive percentage change in annual rainfall. Results further reveal that several extreme weather events with very heavy rainfall may occur in the future. However, the frequency of these big events may not occur too often. This study also discovers that all types of RWH systems are affected by the projected future rainfall, when there is large water demand and/or the storage capacity of the system is limited.
When considering the overall RWH system, the residential sector RWH is more affected than non-residential sector systems. Climate change impacts on the RWH systems are inevitable. Mitigation steps should be incorporated into the initial phase of the system design to reduce these impacts.
Considerable variation on rainfall pattern changes and the degree of severity is found at the Colombo study site. Climate change can affect the hydrological performance of RWH systems in Colombo. The current rate of urbanization in Sri Lanka will result in higher demands for resources, including access to water. RWH is a viable option if it is incorporated with possible future climate change impact design.