Impact of climate change on reservoir reliability

Research and observations indicate that increases in atmospheric carbon dioxide (CO2) are raising global and regional temperatures, and producing changes in other climate variables that drive the terrestrial hydrological cycle, most notably precipitation and potential evaporation. This paper presents results of a study conducted to evaluate the possible impacts of climate change due to doubling of atmospheric carbon dioxide on the reliability of Mazowe reservoir in Zimbabwe. The reservoir supplies most of its water to citrus plantations. Thirty years (1961-1990) of hydrological data (reservoir inflows) and meteorological data were collected from the Zimbabwe National Water Authority (ZINWA) and Department of Meteorological Services, respectively. Outputs from the Canadian Climate Centre (CCC) model for the 2CO2 temperature and rainfall scenarios were used in the study. The Penman model was used to estimate potential evapotranspiration, while reservoir catchment runoff was simulated using the Pitman lumped conceptual model. Research findings revealed that doubling of CO2 in 2050 would significantly increase mean monthly temperature by 3oC, potential evapotranspiration (11.8%), rainfall (15%), runoff (235%) and annual reservoir yield (20.4%) at the 10% risk level. Based on the research findings, appropriate mitigation measures should be employed to minimise high rates of evaporation from the reservoir. On the other hand, the predicted high reservoir yield requires an increase in water use activities such as extension of irrigated area.