Environment: Earth's Creeping Deserts

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Droughts and crop failures have always been a harsh fact of life in arid regions. But the Sahel's calamity was worsened by distinctly modern factors. Improvements in public health had vastly expanded population. New wells lulled the Africans into thinking they were no longer so completely dependent on the slim rainfall. They enlarged their herds and planted more cash crops like cotton and peanuts. For a while, the land withstood the strains. But when the rains ceased, the crops failed and the cattle stripped the fields of virtually every blade of grass around the overworked wells. Soon the thin layer of topsoil vanished, and there was nothing but rock, sand and dust. The Sahara had won.

Other countries have committed the same sad mistakes. In the Sudan, which could be turned into the pita basket of the Arab world, traditional crop rotation has been all but abandoned—with disastrous reductions in yields. In Tunisia, mechanized plowing cut so deeply into the thin layer of topsoil that much of it loosened and blew away.

Land erosion has also been accelerated by the cutting of trees for firewood and farming of marginal lands, leaving the soil unprotected against winds or heavy rains. In Peru and Chile, some hillside terraces now look as barren as the moon, and clear-cutting of Brazil's Amazon rain forests has left great swaths of worthless sunbaked earth. In the foothills of the Himalayas, the watershed has been so badly damaged by the quest for firewood and farm land that mud is now sliding into the major rivers—the Indus, Ganges and Brahmaputra. Because the uplands are no longer able to retain much water, the entire region is threatened with what British Economist Barbara Ward calls "a fatal alternation of drought and flood."

Another factor has been overgrazing, and the goat—valued and bred in great numbers by desert people for its milk and meat—has probably been the greatest villain. Watching this hardy animal tear up almost every shrub or blade of grass in sight, some observers have suggested, only jokingly, that desertification could be quickly stopped in much of Africa or the Middle East if the goat were to suddenly disappear.

The new wastelands created by man may be self-perpetuating. Climatologist Reid Bryson of the University of Wisconsin notes, for example, that the winds that sweep over India's Rajputana desert are rich in moisture; yet little, if any, rain ever falls. Why? According to Bryson and his Indian colleagues, the dust—much of it created by man-caused erosion—is so thick that it acts like a lid, preventing the formation of warming updrafts that would turn the overhanging moisture into rainfall.