Reservoir operation under variable climate: Case of Rozva Dam, Zimbabwe

The challenge of maintaining or improving the quality of rural livelihoods against the increasing threat of climate change (CC) and climate variability (CV) calls for the development of robust and tested systems, tools and procedures for the management of water resources. The research aimed at assessing reservoir operation under variable climate for Rozva Dam, a medium-sized reservoir in Zimbabwe. Rozva Dam is located in the Bikita District of Zimbabwe and has a full supply capacity of 2.8 Mm3 at a maximum water level of 17.3 m. The research analysed 46 years of rainfall and temperature data to assess climate variability and or change. The CROPWAT model was used to estimate crop water requirements for the adjacent 80 hectare irrigation scheme. The WAFLEX model was applied to simulate the performance of the system under three scenarios: (1) existing demands and operational rules, (2) reduced water availability due to climate change, as predicted by the Ministry of Mines, but with increasing annual demands and (3) climate change situation coupled with change in irrigation technology. The results show a general decreasing linear trend for rainfall although the variance was not statistically significant at p = 0.05. A clearer cyclic pattern was observed for the decadal analysis. An increasing trend in both maximum and minimum temperature was observed although, again, these were not statistically significant with a Spearman’s rank correlation coefficient (Rsp) of below 0.5. The research used rainfall and temperature data as the basis for confirmation climate change and variability in the study area. Analyses show that the area is experiencing more of CV than CC. Modelling results show that the reservoir can satisfy current demands but will fail to cope under the forecasted increase in demand. The conclusions from the research are that the available water resources in the studied system are sufficient to satisfy the current demands. The predicted level of climate change will result in shortages of up to 30% for the downstream users necessitating the need to review how the reservoir is operated. Water managers and policy makers should therefore promote awareness of anticipated consequences of climate change so that communities are better prepared to cope with CC and CV.