Article by Adrian Reid

10 May, 2020

In the 1980s, Africa's Sahel region, just south of the Saharan desert, went through a five-year drought that killed thousands. Scientists are now predicting a drought lasting decades, if not centuries for the region.

Article by Adrian Reid

10 May, 2020

A 350-year long drought

On the southern edge of the Saharan Desert, the Sahel region is exactly where you would expect the world's worst droughts to take place.

The Sahel drought of 1983-1988 is noteworthy for its length and deadliness. In the five years it lasted, 300,000 died from the drought in Ethiopia and in the Sudan, 150,000 died.

U.S. researchers suspect that this may be minor compared to the mega-droughts that took place not long ago.

In 2009, a team of researchers from the University of Texas and the University of Arizona measured tree rings from submerged trees in Lake Bosumtwi, Ghana, to create a history of droughts going back for thousands of years. They started to see a pattern in the cycle and length of droughts in the area.

The researchers could see the frequent occurrence of droughts lasting 30-60 years, which matched changes in sea temperatures in the Atlantic Ocean. The tree ring record also showed that several droughts lasted a century or more, with one recent mega-drought continuing for 350 years.

Because the pattern of mega-droughts is so regular, the scientists believe that "we will eventually shift back into a period of centennial-scale drought conditions". They believe this is even more likely with climate change and rising global temperatures.

The Sahel region of Africa. Munion, CC BY-SA 3.0

Conditions 'unprecedented'

French researchers say that the Sahel is already moving towards long-term drought.

By looking at seashells in Senegal and measuring the lines and also their chemical composition, the scientists could create a record of droughts for the last 1600 years in the West Sahel.

Their conclusion - "the Western Sahel appears to be experiencing today unprecedented drought conditions."

Since the 1960s, rainfall has dropped by 30%, leading to a "severe multi decadal drought that represents one of the most significant climate change episodes in the global instrumental record".

A 6800-year-old mollusk collected from Peru’s Ica valley. The shells record the temperature of the ocean during their 1 to 3-year lifetime.Matthieu Carré / University of Montpellier

Drought increasing across Africa

It's not just the Sahel, increasing drought is a disaster for the whole of Africa. "The frequency, intensity and geospatial coverage of droughts have significantly increased across the entire African continent during the second half of the 1900–2013 period".

The reasons for drought are different for each part of Africa. For Southern Africa, the cause is La Niña. For East Africa, it's El Niño. These Spanish terms refer to changes in sea temperatures in the Pacific Ocean which can affect the weather around the world.

Large tropical trees submerged in 15-20 metres of water provide evidence of severe, long lasting droughts just a few centuries ago. Lake Bosumtwi, Ghana.J.T. Overpeck and W. Wheeler, University of Arizona, permitted use

For the Sahel, the cause of drought is more complex, but the U.S. scientists who counted tree rings in Lake Bosumtwi, Ghana, saw a match between mega-droughts and changing sea temperatures in the Atlantic Ocean.

When sea temperatures in the North Atlantic warm, there's more rain in the Sahel. And when the North Atlantic cools, there's drought. The reason why sea temperatures change so much is another story, but they are now beginning to drop. It seems likely that the Sahel is ready for another period of drought for decades.