Climate and Africa: why the land goes dry - part 1

Science News, May 4, 1985 by Stefi Weisburd, Janet Raloff

But, according to the University of Maryland's Shukla, no really comprehensive numerical experiments have been carried out for Africa, and results from studies done for other regions cannot simply be applied to the Sahel. Until global circulation modelers begin focusing on Africa, he says, any scenarios on what causes its droughts will be total conjecture.

Chervin adds that the cost of running such experiments is very high--about $2,000 per hour on a Cray-1 computer--so one had better first be very sure of the model. The weakest point of models today, Shukla and others agree, is their treatment of interactions between the atmosphere and land. But Piers Sellers, at NASA's Goddard Space Flight Center in Greenbelt, Md., believes that within two years models should be able to start providing some answers.

Models are of little use, however, without good observational data to put into them. That's why researchers at a recent State Department seminar focusing on the African drought stressed a need for better data collection and communication. "There is an inadequate reporting network over Africa, and in particular over the sub-Sahara,' Rasmusson said. "This network has actually been deteriorating over the last quarter century.'

Nicholson feels that the biggest problem for rainfall data is not collection but transmission. Many of her rainfall measurements have to be hand copied, requiring periodic travel to Africa. Also severely lacking from many countries is up-to-date archiving of data. It's been particularly difficult to obtain information from areas like Chad and Ethiopia because of political problems such as war. Lack of data from these areas is considered especially serious because the climate there is thought to be driven by forces quite different from those in the west Sahel.

There is also a dire need for upper-air data on temperature, wind flow and pressure --information crucial to understanding the dynamics of the atmosphere. Very few countries have balloons to take these measurements, Nicholson says.

Remote sensing surveys from satellites are beginning to provide important information, from cloud cover to temperatures of atmosphere and ocean. Satellite observations may also aid studies of land and climate by measuring soil surface temperatures and by mapping vegetation. In providing a big picture of how land conditions change between ground stations, remote sensing helps researchers obtain global data quickly without relying on information networks between countries. But Sellers cautions that there are some types of data that satellites will never be able to measure directly, like moisture below the soil surface. So remote sensing is not a replacement for good ground and balloon measurements.

Because of the large-scale nature of droughts and the atmospheric and oceanic systems that may bring them on, it's doubtful that people will ever be able to control these phenomena. At best, "solutions' to the problems lie with predictions and preparations for dry periods. But drought predictions are a long way off. As for the present drought, says Nicholson, "We have no way of forecasting how long it is going to persist. It could end; it could continue. We just don't know.'