A Framework for Determining the Possible Impacts of a Changing Climate on Water Supply

For effective water resources management, all "stressors" that may impact on balancing future water supply and demand must be assessed. Hydrologists have recently begun making headway towards assessing a previously ignored "stressor", viz. the impact of a changing climate. At Umgeni Water, a bulk water utility in South Africa, a process has been initiated to quantify potential impacts, initially on strategic catchments using daily physical-conceptual hydrological modelling. Preliminary results indicate that streamflow could increase by up to 2.6 and 5.3 fold by the year 2065 and 2100 respectively, mostly in the currently dry winter months. Furthermore, inter-annual variability could decrease. This could increase risks of flooding and compromise dam safety. Should additional streamflow improve water yields, climate change could potentially benefit cash flows by delaying capital expenditure on projects to improve assurance of supply. Regardless, it is imperative that the hydrological consequences of a changing climate be included in water development, disaster risk and system operating plans.