Forecast shows Africa to face river crisis

Africa's rivers face dramatic disruption that will leave a quarter of the continent severely short of water by the end of the century, according to a global warming study published on Friday.

In the first detailed assessment of climate change on the continent's waterways researchers found that watercourses on the continent are highly sensitive to shifts in rainfall patterns. Even modest decreases in rain in western Africa will see rivers lose as much as 80% of their water, triggering a surge of what the scientists call "water refugees".

Maarten de Wit, a climate expert at the University of Cape Town who led the study, said the redrawing of Africa's waterways will pose serious political problems as people displaced by droughts are forced into other countries to be near water.

"In those areas where people have little water as it is, it's going to have a devastating effect," he said. "If you're already walking 5km to the nearest stream to get water it's going to mean walking 30km or moving your whole household.

The study, which appears in the journal Science on Friday, is the first to identify how Africa's rivers will respond to climate change over the century. The extent to which slight changes in rainfall could impact on rivers had never been realised.

The researchers used a computer to divide the continent into 1 000km wide squares and worked out the total length of streams and rivers in each block. They used climate change models to calculate the expected changes in rainfall across the continent and the effect they would have on river levels. The scientists found that in 75% of the countries, those that received between 400mm and 1 000mm of rain a year, shifts in rainfall caused larger than expected rises or falls in river levels. In Harare a 10% drop in rainfall is expected to lead to an 81% drop in fresh water from rivers, a situation the scientists believe will be mirrored in Madagascar, eastern Zambia and Angola.

South Africa, which is experiencing a prolonged drought, can expect far less water from the Orange river. A 10% fall in rain over Johannesburg and Bloemfontein will lead to a 70% drop in river levels.

The study predicts rain will increase over East Africa. Climate change is expected to bring 10% more rain to Tanzania before the end of the century, boosting water course levels by 136%, while Somalia faces a 20% rise in rainfall, leading to more than a 1 000% increase in the water it receives from waterways. However, increased rainfall could lead to more standing water, more mosquitoes, and widespread malaria. - Guardian Unlimited © Guardian Newspapers Limited 2006