This report gives an early warning about what southern Africa could be facing as countries contemplate plans for more large hydropower dams in a time of climate change. The report finds that existing and proposed hydropower dams are not being properly evaluated for the risks from natural hydrological variability (which is extremely high in the Zambezi), much less the risks posed by climate change. The report’s key findings describe a region moving toward the edge of a hydrological precipice. The Zambezi basin exhibits the worst potential effects of climate change among eleven major sub-Saharan African river basins and will experience the most substantial reduction in rainfall and runoff. Furthermore, more frequent extreme floods threaten the stability and safe operation of large dams. The report recommends a series of steps to address coming hydrological changes, including changes to how dams are planned and operated.