for National Geographic News
Many climate scientists already predict that less rain will fall annually in parts of Africa within 50 years due to global warming.
Now new research suggests that even a small decrease in rainfall on the continent could cause a drastic reduction in river water, the lifeblood for rural populations in Africa.
A decrease in water availability could occur across about 25 percent of the continent, according to the new study.
Hardest hit would be areas in northwestern and southern Africa, with some of the most serious effects striking large areas of Botswana and South Africa.
Geologists Maarten de Wit and Jacek Stankiewicz of the University of Cape Town in South Africa conducted the research. Their findings appear in the current edition of the online journal Science Express.
To predict future rainfall, the scientists compared 21 of what they consider to be the best climate change models developed by research teams around the world. On average, the models forecast a 10 to 20 percent drop in rainfall in northwestern and southern Africa by 2070.
The researchers then juxtaposed these rainfall predictions with measurements of Africa's rivers to gauge the future of Africa's water supply.
With a 10 percent drop in rainfall, parts of Botswana (map) would be left with just 23 percent of the surface-water flow it has now, their study showed.
With a 20 percent decrease, Cape Town would be left with just 42 percent of its river water, and "Botswana would completely dry up,'' de Wit said.
In parts of northern Africa, river water levels would drop below 50 percent.
"It's like erasing large sections of the rivers from the map,'' de Wit said of the findings.
Areas in Danger
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