In summary, mean and extreme streamflow changes are projected over most of the ice-free land surface . The magnitude of streamflow change is projected to increase with global warming in most regions , but there is often high uncertainty on the sign of change. There is high confidence that mean streamflows will increase in the northern high latitudes and decrease in the Mediterranean and southern Africa. Annual mean runoff in one third of assessed glacierised catchments is projected to decline by at least 10% by 2100 under RCP4.5, with the most significant reductions in central Asia and the Andes . Elsewhere, projections include both increased and decreased flows. Substantial fractions of ensemble projections disagree with the multi-model mean , with implications for long-term planning for water management. With 1.5 and 2°C global warming, approximately 15 and 20% of the current global population, respectively, would experience both an increase in high streamflows and a decrease in low streamflows . At 4ºC global at the end of the century, 10% of the global land area is projected to simultaneously experience an increase in high extreme streamflow and decrease in low extreme streamflow.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report