Here we provide the climate change data from the Coupled Model Intercomparison Project phase 6 (CMIP6) used in an assessment of future water security of two Brazilian basins: Guariroba River basin and Jaguari River basin responsible for supplying water to Campo Grande city and the São Paulo Metropolitan Region, respectively. The basins' hydrological response was simulated using the SWAT+ model considering three climate change scenarios from a CMIP6 multimodel ensemble: SSP2-4.5 (medium forcing), SSP3-7.0 (high forcing), and SSP5-8.5 (high forcing). The ensemble was constructed using seven General Circulation/Earth System models (variant ID r1i1p1f1 and further processed for bias correction using quantile delta mapping. The manuscript of "Water security in an uncertain future: contrasting realities from an availability-demand perspective" has been published in Water Resources Management, please find it here.