A review of river flow and lake level changes in 82 basins in eastern and southern Africa regions for 1970-2010 showed mixed trends: 51% had decreasing trends ranging from 10-49% and 11% increasing trends ranging from 7-60% . However, in southern Africa as a whole, river flows have mostly decreased  . In east Africa, large rivers such as the Tana show increasing flow  related to increased rainfall in the highlands, with little influence of flow regulation by a series of dams . The Nile river basin has been experiencing a mainly increasing rainfall trend upstream and decreasing trend downstream . The observed changes are driven by a complex coupling of changes in climate, land use and water demand.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report