11 May 2009

New Research Reveals Droughts Common in West Africa

Severe droughts, some lasting centuries, occurred during past 3 millennia

Tropical trees submerged in 15 to 20 meters of water provide a record of past droughts. (Courtesy J.T. Overpeck and W. Wheeler)

By Daniel Gorelick
Staff Writer

Washington — The decades-long drought that began in West Africa in the 1960s is not an anomaly compared with what the region has faced during the last three millennia.

An analysis of sediment from a crater lake in Ghana shows periods of severe drought lasting from decades to centuries throughout the last 3,000 years, according to a study published in the April 17 issue of Science magazine.

“What’s disconcerting about this record is that it suggests that the most recent drought was relatively minor in the context of the West African drought history,” geologist Timothy M. Shanahan, lead author of the study, said in an April press release.

The most recent megadrought, or centuries-long drought, lasted more than three centuries, between 1400 and 1700. “If we were to switch into one of these century-scale patterns of drought, it would be a lot more severe and it would be very difficult for people to adjust to the change,” Shanahan said.

Sediment analysis showed that West African droughts occurred during relatively warm and cool periods of the Earth’s history. The recent megadrought coincided with the Little Ice Age of 1400 to 1850, when temperatures in the Northern Hemisphere were lower than they are now.

Scientists cannot yet predict how climate change will affect the frequency or duration of future droughts, geologist Jonathan Overpeck told America.gov. “We can be confident that droughts will continue to occur, and that decades-long droughts should be a very real concern.”

As global temperatures rise, droughts will occur under hotter conditions, more severely affecting natural vegetation, agriculture and water supplies, according to Overpeck, a co-author of the study.

“Some studies suggest more drought, some less,” Overpeck said. “It would be against great odds to bet that the region will become free of drought.”

RESPONDING TO FUTURE DROUGHT

Although making immediate changes to reduce global warming likely will help mitigate the effects of future droughts, this is not enough to reduce human suffering and economic hardship, according to Overpeck.

A lake’s sediment core provides a high-resolution chronology of past climate variations. (Courtesy T.M. Shanahan and W. Wheeler)

“Our work makes it clear that we must also work to make the people of sub-Saharan Africa more resilient to drought and its impacts.”

Overpeck points to the dry, southwestern United States as a model for how scientists can work with local groups to design and implement a plan for dealing with drought.

There scientists work with local water, forest, wildfire and park and recreation managers, as well as farmers and ranchers, to learn what climate studies would be most useful for the region and to make existing climate knowledge more useful. The group, called Climate Assessment for the Southwest (CLIMAS), sees engaging with locals as crucial because they can help create policy as well as or better than the scientists, Overpeck said.

When the current drought in the southwestern United States began in 1999, CLIMAS “played a big role in designing and implementing a drought plan for the state of Arizona,” Overpeck, who is a member of CLIMAS, said.

He thinks that “in Africa, it would be ideal to do the same thing.” Scientists need to build trust and partner with locals so that communities are willing to implement plans to reduce vulnerability to drought. “This isn’t the kind of thing that can be done in one or two visits, but rather requires sustained interactions.”

DROUGHT-RESISTANT PLANTS

While climate scientists work to predict the frequency and severity of future droughts, biologists are researching ways to make plants more resistant to drought.

An international team of scientists discovered a gene that improves plant tolerance to drought. The team’s results, which will appear in the May 22 issue of Science magazine, suggest that chemicals that turn on this and related genes one day could be used to improve crop yields during drought.

“I am very optimistic that a chemical contribution to the drought problem is feasible,” said lead researcher Sean Cutler, a biologist at the University of California in Riverside. “However, until we have the right molecules in hand, we can’t say anything with absolute certainty.”

Cutler wants policymakers to make this strategy a priority. “The resources for basic research in plant biology are very meager,” Cutler told America.gov. “I would like to see the development of these kinds of molecules a major priority at funding agencies.”

As for competition from other researchers, Cutler welcomes it.

“I would be thrilled if others get in on trying to realize this goal and try to beat me to the punch at my own mission. I think this is a huge problem and we need armies of labs working to solve it.”