A meteor helps reveal West Africa's troubling drought history

How do you help cities, towns, and villages build resilience to drought when droughts can last for more than a century, not "merely" decades?

That's a question scientists have posed through a new record of drought in western Africa. It stretches back some 3,000 years. And it reveals a couple of sobering features.

First, droughts similar to the Sahel drought of the 1970s and '80s, in which rainfall amounts fell by some 30 percent, pop up on average every 30 to 60 years.

Second, this drought, which aid and public-health officials say killed some 100,000 people and prompted millions to migrate, was a hydrological piker. So-called megadroughts lasting nearly a century or more have occurred six times in the last 2,700 years. Two of those took place in the last 1,000 years. The most recent occurred between 550 and 200 years ago.

For people living in the United States, especially out west, this is – or should be – a familiar message. Research into the US West's hydrological history has uncovered evidence of droughts over the past 1,000 years or more that were more intense, covered a wider swath of the country, and lasted far longer than anything the 20th century offered up.

For West Africa, the record is disconcerting, says Timothy Shanahan, an assistant professor of geosciences at the University of Texas at Austin. "It suggests that the region is vulnerable to larger and longer-lasting droughts than we have seen in our lifetime. Were we to shift into one of these century-scale patterns of drought, it would be a lot more severe and a lot more difficult for people to adjust to these changes."

The record "is going to be challenging for policymakers and planners," says Dr. Shanahan, who spearheaded the study and wrote up the results, published in the April 17 issue of the journal Science.

It's worth noting that no one is talking global warming regarding these results. Just "natural" variability.

Add human-triggered warming to the picture, however, and it makes the challenge of adaptation that much greater, notes Jonathan Overpeck, a geoscientist at the University of Arizona in Tucson and head of the University's Environmental Studies Laboratory.

Climate scientists "have strong confidence that continued warming will take place in the absence of reductions of greenhouse gases," says Dr. Overpeck, one of the paper's co-authors. "Even if we reduce greenhouse gases somewhat, we're likely to have an increase in temperature in this region over this century in excess of 5, even 10 degrees Fahrenheit. That could make the droughts, when they occur, much harder to adapt to."

Even without global warming in the picture, the study's implication for the region "is depressing," says Peter Bloch, an economist with the University of Wisconsin at Madison's forestry and wildlife ecology department who works in the region.

He notes that over the past 20 to 25 years,  West Africa has experienced very little starvation, in spite of rapid population growth. "It's a major achievement to be feeding three times as many people as there were 25 years ago," and with less rain.

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