Using predicted precipitation changes, we calculate that decrease in perennial drainage will significantly affect present surface water access across 25% of Africa by the end of this century.
I don’t want to make too big a deal of this. I think Vörösmarty et al. were right six years ago when they wrote:
(R)ising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question.
Whatever the global climate change component, natural variability on decadal scales along with population growth and movement pose serious problems.