March 03, 2006 (Johannesburg) - Changes in rainfall as a result of global warming could leave one quarter of the African continent dry by the end of the century, according to a study by South African scientists.

The study published in the the scientific journal Science on Thursday took into account the loss of water drainage from lakes and rivers across the continent, using climate models for the 21st century.

Maarten de Wit and Jacek Stankiewicz of the University of Cape Town stated: "Using predicted precipitation changes, we calculate that the decrease in perennial drainage with significantly affect present surface water access across 25 percent of Africa by the end of this century".

For some of the driest parts of the continent, such as most of southern Africa and southern Madagascar the impact would be most severe, the study found.

Eastern and northern South Africa was expected to experience strong to moderate decreases in water supply, according to the study that noted western South Africa was currently experiencing its worst drought in 100 years.

Any water loss in eastern South Africa would affect the upper reaches of the 11 000-kilometre Orange river, one of the five largest rivers in Africa, the scientists said.

With at least five instances of this river running dry between 1862 and 1912 with a total halt to its flow over two months in 1903, even one of the continent' biggest rivers cannot be truly called perennial, the study observed.

De Wit and Stankiewicz also identified the east-west band that stretches from the west African state of Senegal to Sudan in the east and separates the "dry Sahara from wet Central Africa" as a major vulnerable area.

The area crosses a number of important water bodies, such as the Sudd swamps in the Nile Basin, Lake Chad that has already shrunk to 10 percent of its size in 1963 and the Niger River.

Data gathered for the study, suggests that the Sahara desert would spread south from Burkina Faso and Mali, researchers said.

In Africa, where droughts already occur regularly and people depend on local water sources, climate driven changes in water supplies potentially have devastating implications, it was noted.

The results of their study, the researchers said, provided African states with an opportunity to focus responses on rural areas where the risk of future water loss and scarcity has been determined high. - Sapa-dpa