The African Sahel -- the semi-arid zone south of the Sahara -- may at last be nearing the end of its long-playing drought. But the new findings that encourage this hope also reinforce the suspicions of many meteorologists that recurring drought is a normal part of Sahelian climate.
Using river runoff data as a rainfall indicator, Hugues Faure of the Laboratory of Quaternary Geology at Marseille and Jean- Yves Gac of the Office of Overseas Scientific and Technical Research at Dakar find a cyclical pattern of dry and wet periods. The River Senegal's pattern of annual discharge is typical. Throughout the 19th century, it shows short periods of drastic minimum followed by a slow return to longer periods of wet conditions with a double maximum, the two French scientists say in discussing their findings in the journal Nature.
These features also characterize a graph of 20th-century data. The average time between the last three droughts is 31.3 years with extreme conditions recurring every 10.3 years, give or take four years. Extrapolating these data "suggests that the present drought should end in 1985 with full wet conditions being re-established in about 1992," the scientists say. However, they warn, "If the same pattern continues, it is feared that a severe drought will occur around 2005."
Thus the extreme dryness that aroused international concern for the region in the late 1960s and early 1970s was not an anomaly to be endured and forgotten. The extensive suffering and economic losses it produced should be taken as a warning that population growth and land-use patterns that emphasize extensive cattle grazing are putting more pressure on the area than it can sustain in the long run.
The problems of the Sahelian people dropped out of the news after near-normal rains in 1974. However, the region now has had a dozen consecutive years with rainfall below what had once been considered normal. The monsoon rains, on which the region is largely dependent, have yet to return to what had been considered their full force.
If the Faure and Gac pattern does repeat and plentiful rains return within a few years, the region's burdens will ease. This would be no blessing if it diverted attention from a need to develop an economy and living patterns that can be sustained through the driest of times.
As Faure and Gac note, their findings are consistent with a variety of studies which have shown great variability of rainfall to be a main feature of Sahelian climate for many thousands of years. There are many uncertainties in such studies. No one knows what the complex causes of this climatic pattern may be. Nevertheless, one point seems increasingly clear. People who live in the Sahel or in other semiarid zones must consider what they now call "drought" to be par t of their normal weather.