This paper examines climate change impact on hydropower will affect the expansion of the regional electricity system, as well as system costs and greenhouse gas emissions. The output from major Zambezi hydropower plants could decline by 10-20% under a drying climate, while wetting of the basin produces only a marginal increase. At a regional level, the increases in electricity generation costs are relatively small (less than 1% over the long term), but could reach 20-30% in the near term for hydro-dependent countries (e.g. Mozambique and Zambia). Because some hydropower could be displaced by coal, regional greenhouse gas emissions could increase by the equivalent of a large coal-fired power station. The risks to regional electricity systems highlight the need for strong cooperative governance arrangements to manage shared water resources in the region, which could be bolstered by recent political initiatives. Beyond the level of individual investments, a policy shift is needed to integrate climate change and upstream development considerations into national and regional electricity planning, supported by relevant tools. In addition, the potential for increased carbon emissions has implications for the commitments of southern African countries under the Paris Agreement to the UNFCCC.