6,000 Years Ago The Sahara Desert Was Green And Rainy

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The Sahara Desert was a lush tropical grassland as little as 6,000 years ago – what happened? How did this vegetated area, which received plentiful rain, become some of the most arid, dry land on earth.

It has to do with shifts in the worlds weather patterns, and researchers are searching for a clue to this tremendous transformation in climate. A Robert Korty from Texas A&M is leading this research and in doing so hopes this will be helpful in the prediction of future rainfall patterns worldwide.

Researchers have looked into the present movements of the intertropical convergence zone, which is an area of extreme tropical rainfall, and compared these with the rainfall patterns of the Holocene era. Researchers found rainfall pattern links from thousands of years ago, with the use of data and computer models.

These two researchers are – associate professor. Robert Korty – department of Atmospheric Sciences, and William Boos, who is a colleague and is from Yale University. Together they have had work published in an issue of Nature Geo-science.

To help them understand why the heaviest tropical rainfall belts set up as they do they have developed a framework Through the Hadley circulation, tropical rain belts are tied to what happens in other areas of the world. As the chain of events is very complex, it won’t predict direct changes elsewhere, but that is the goal. Rising near the equator is a tropical atmospheric circulation known as the Hadley Circulation. Positions of severe storms, tropical rain belts, hurricanes, subtropical trade winds, and the jet stream are all linked to this.

Beneath the descending part of the Hadley circulation, desert-like conditions can be created – even in the subtropics. Some of the aridest regions on Earth are located beneath descending parts of the Hadley circulation.

It has been somewhat of a mystery, as 6,000 years ago the Sahara was a lush area, with ample rainfall. How did the Tropical rain belt move so far north of the equator? It has been found that while the belt doesn’t necessarily move much, large migrations in rainfall can occur in a different part of the globe. Finding better ways to predict world rainfall patterns could result from this study.

It would be beneficial if details of how tropical rain bands shift during El Niño and El Niña events could be predicted using this framework. These are the warming or cooling of waters which tend to influence world weather patterns – water s of the central Pacific Ocean.

Deducing how the position of rainfall changes in response to individual forces is just one of the implications. The amount of rain that geologic evidence shows fell over what is now the Sahara Desert could not have been sustained by the variations in the Earth’s orbit 6,000 years ago. These
themselves could not have shifted the rain belt over North Africa.

By Debbie

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