Changes in runoff and streamflow are projected over most of the ice-free land surface with all recent climate and hydrological model ensembles . Changes in streamflow could increase the number of people facing water scarcity or insecurity  . Projections of future runoff at basin scales show considerable uncertainty in many regions, including differences in signs in many regions . This uncertainty is driven by uncertainties in regional precipitation patterns and hydrological models , including vegetation responses to CO2 and its effects on ET . This uncertainty in future water availability contributes to the policy challenges for adaptation, for example, for managing risks of water scarcity . In many regions, some models project large changes in runoff/streamflow but with low consistency between models on the sign of the change . In streamflow projections driven by 11 CMIP5 models with the RCP8.5 scenario, strong model consistency  is only seen over 21% of global land . Consensus on the sign of projected change is smaller with the RCP4.5 scenario.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report