`Ancient megadrought struck 16,000 years ago`

The drought was so intense that it dried out Africa`s Lake Victoria.

Updated: Mar 04, 2011, 10:43 AM IST

Washington: An intense and far-reaching dry spell that parched Africa and southern Asia about 16,000 years ago was one of the most expansive megadroughts in the history
of modern humans, a new climate research has found.

An international team of scientists led by Curt Stager of Paul Smith`s College, New York, has compiled four dozen paleoclimate records from sediment cores in Lake Tanganyika and other locations in Africa.

The records showed that one of the most widespread and intense droughts of the last 50,000 years or more struck Africa and Southern Asia 17,000 to 16,000 years ago.

The drought was so intense that it dried out Africa`s Lake Victoria -- the world`s largest tropical lake -- as well as Lake Tana of Ethiopia and Turkey`s Lake Van, found the study that appeared in the journal Science. The Nile, Congo and other major rivers shrivelled, and Asian summer monsoons weakened or failed from China to the Mediterranean, meaning the monsoon season carried little or no rainwater, according to the researchers.

Paul Filmer, program director in the National Science Foundation`s (NSF) Division of Earth Sciences, which funded the research, said between 18,000 and 15,000 years ago, large amounts of ice and meltwater entered the North Atlantic Ocean,
causing regional cooling but also major drought in the tropics.

"The height of this time period coincided with one of the most extreme megadroughts of the last 50,000 years in the Afro-Asian monsoon region with potentially serious
consequences for the Paleolithic humans that lived there at the time," Filmer said in a statement.

The "H1 megadrought", as it is known, was one of the most severe climate trials ever faced by anatomically modern humans, he said.

What caused the megadrought remains a mystery, but its timing suggested a link to Heinrich Event 1 (or "H1"), a massive surge of icebergs and meltwater into the North
Atlantic at the close of the last ice age.

Previous studies had implicated southward drift of the tropical rain belt as a localised cause, but the broad geographic coverage in this study paints a more nuanced

"If southward drift were the only cause," Stager said, "we`d have found evidence of wetting farther south. But the megadrought hit equatorial and southeastern Africa as well, so the rain belt didn`t just move -- it also weakened."

Climate models are yet to simulate the full scope of the event. The lack of a complete explanation opens the question of whether an extreme megadrought could strike again as the world warms and de-ices further.

"There`s much less ice left to collapse into the North Atlantic now, so I`d be surprised if it could all happen again -- at least on such a huge scale," Stager added.