Reservoir Operation Under Different Climate Change Scenarios: Case of Roswa Dam, Bikita District, Zimbabwe.

Abstract

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 aim of this research was to assess reservoir operation under different climate change scenarios for a medium-sized reservoir in the Bikita District of Zimbabwe. The research tested for trends to confirm climate variability and/or climate change from daily rainfall and temperature data over the period 1954-2000. The CROPWAT model was used to establish crop water requirements for the existing 80 hectare Roswa irrigation scheme. The WAFLEX model was applied to simulate the performance of the system under three scenarios: (1) existing operational rules, (2) reduced water availability due to CC and, and accommodation of projected increased demands for urban use, agriculture, the environment and downstream uses and (3) change in irrigation technology. The results obtained show a general decreasing linear rainfall trend, although the change was not significant at R2 of 0.009. A clearer cyclic pattern was obtained for the decadal analysis implying 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 when the planned agricultural expansion is doubled and other demands increase. The conclusions from the research are that the available water resources in the studied system are sufficient to satisfy the current demands. Climate change, together with projected demands will result in shortages of up to 30% for the downstream users. Rationing at 20% would be experienced 24% of the time. The introduction of more efficient irrigation technologies would result in a reduction in these shortages from the current 30% to 24% and 3% for sprinkler and drip irrigation systems respectively. It was therefore concluded that, although the area is experiencing variability in climate, there is enough water in the reservoir to satisfy current demand. Projected changes in climate together with projected demands would lead to shortages, particularly for the downstream users. Policy makers should therefore create awareness in the community so that water users are aware of anticipated consequences of climate change and can adapt accordingly.