One country on the opposite side of Africa where that scenario may already have started to play out is Mali, the third poorest nation in the world, where rainfall levels have been in decline for the past 30 years across the semi-arid Sahel region.

CNN: Climate change 'to create 1B refugees'

Farmers soak up about 85% of the border region's scarce water, and on the semi-arid land on both sides they grow thirsty cash crops like sugar cane.

ECONOMIST: IOU H2O