By Richard Black
Environment correspondent, BBC News website
Severe droughts lasting centuries have happened often in West Africa's recent history, and another one is almost inevitable, researchers say.
Analysis of sediments in a Ghanaian lake shows the last of these "megadroughts" ended 250 years ago.
Writing in the journal Science, the researchers suggest man-made climate change may make the situation worse.
But, they say, the droughts are going to happen again anyway, and societies should begin planning for them.
"It's disconcerting - it suggests we're vulnerable to a longer-lasting drought than we've seen in our lifetime," said Tim Shanahan from the University of Texas in Austin, who led the research team.
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more:
http://news.bbc.co.uk/2/hi/science/nature/8003060.stm