Impact of Climate Change and Consumptive Demands on the Performance of Sao Francisco River Reservoirs, Brazil

Climate change in the coming decades could intensify extreme events such as severe droughts. Combined with the possible increase of water demands, these changes exert a great deal of pressure on the water systems. In order to confirm this assumption, a set of scenarios was proposed in this study to consider the combined impact of climate changes and the increase in water demand on the main multiple-use reservoirs of Sao Francisco River, Brazil. For this purpose, five CMIP6 climate models were used, considering two greenhouse gas emissions scenarios: the SSP2-4.5 and SSP5-8.5. The affluent natural flows and regulated flows were estimated to the adopted reservoirs considering all existing, new and projected demands. The combination of scenarios indicated an increase in Potential Evapotranspiration; possible significant reduction in water availability, with a decrease in precipitation with a magnitude of -15% in the most pessimistic scenarios and a decrease in flows with a magnitude varying between -5% and -40% in the Sobradinho and Tres Marias reservoirs; growth in water demand, mainly for irrigation, with annual rates of 6.80%, 7.42%, 10.99% and 9.29% for Itaparica, Sobradinho, Tres Marias and Retiro Baixo, respectively; and a substantial reduction in the performance of the evaluated reservoirs, mainly for the Retiro Baixo and Itaparica reservoirs, which showed a high vulnerability index and a low sustainability index.