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Africa's drought-prone Sahel region faces "dramatic drying" during the next 50 years because of climate change, according to a new computer simulation.

Although the 'model' contradicts most previous ones, researchers are taking it seriously as it is among the best at simulating 20th century climate — a test of how well models can predict future trends.

The Sahel, which stretches from Senegal to Somalia, was frequently hit by drought during the second half of the 20th century. The region includes parts of Mali, Mauritania and Niger, where drought — together with locusts — caused a major famine this year.

Most models predict that the region will get wetter between now and 2050, so the new results published this week in the Proceedings of the National Academy of Sciences are unusual.

Lead author Isaac Held, of the US National Oceanic Atmospheric Administration, cautions that his team is not claiming to have a definitive answer.

They point out that there are uncertainties about how temperatures in the Atlantic and Indian Oceans, and in the Sahara desert, affect climate in the Sahel. Predictions of future climate should therefore be based on multiple models, they say.

"Our model does a very good job on the 20th century and produces interesting results in the 21st century," says Held.

Several research groups around the world are analysing the model, which has also been submitted to the Intergovernmental Panel on Climate Change, the consortium of scientists that researches the issue and advises the United Nations.

Held says it is unclear why his team's model produces such a dramatically different result for the Sahel, but he thinks it might be related to how the model simulates the behaviour of clouds.

Reference: Proceedings of the National Academy of Sciences doi10.1073/pnas.0509057102 (2005)

Link to abstract of paper by Held and colleagues