This thesis investigates the hypothesis that the combination of future changes in climate and development (primarily irrigation) in the Zambezi River Basin (ZRB) threatens the technical and economic viability of existing and planned hydropower plants, and in turn the expansion plans and costs of the regional power system for Southern African countries. This hypothesis is evaluated using the following three questions to structure the analysis. How could future climate and irrigation expansion in the Zambezi River Basin affect hydropower generation potential? How could development in Southern Africa affect power demand, and how might this demand be met? How could the changes in water availability for hydropower (i.e. due to climate change and development) affect regional electricity expansion plans, generation costs and greenhouse gas emissions?