Future hydropower operations in the Zambezi River basin: Climate impacts and adaptation capacity

Southern Africa could experience major hydrological changes in coming decades, bringing drastic changes to hydropower. Focusing on four large hydropower dams in the Kafue and Zambezi Rivers (Itezhi-Tezhi, Kafue Gorge Upper, Kariba, and Cahora Bassa), accounting for over 90% of the installed capacity in the basin, this study analyzed how these dams have altered river flows in the past, and how hydropower generation could be affected by future climate change and water use scenarios based on dynamically downscaled simulations from the Fifth Coupled Model Intercomparison Project for a Representative Concentration Pathway of 8.5 W/m(2). Future climate change could affect reservoir levels by decreasing water inflows and by increasing evaporation. Results showed a decrease in median annual water levels for all reservoirs, with largest changes expected at Itezhi-Tezhi (-1.3 to -3.3 m), followed by Cahora Bassa (-0.8 to -2.8 m), Kariba (-0.2 to -0.9), and Kafue Gorge (0.1-0.2 m). Flows downstream of dams show a consistent negative trend, with mean annual flow changes of -30% to -49% at the furthest downstream gauge. The combined reduction in water levels and flows could result in decreases on average annual hydropower generation and increases in interannual variability; annual generation could decrease by -61% to -28% at Kariba, by -51% to -21% at Itezhi-Tezhi, by -7% to -39% at Kafue Gorge, and -27% to -9% at Cahora Bassa. Reservoir operation optimization could marginally offset the projected changes in hydropower generation, with largest gains for Kariba (+6%) and Cahora Bassa (+10%). Overall, opportunities to offset losses via operations would probably decrease with the expected drier climate and escalating reduction in river discharge and water availability. Given these negative projections, it is becoming critical to adapt and coordinate reservoir operations to best cope with the expected challenging future in this important river basin.