In addition to human-induced degradation, geophysical events (such as droughts, floods, tornadoes, windstorms, and landslides) and biological events (such as locust and pest invasions) greatly affect the environment and the well-being of people in sub-Saharan Africa. The two most important geophysical events are probably drought and floods. Drought is defined as a period of two or more years during which rainfall is well below average.28 In ecological terms, it is simply a dry period to which an ecosystem may be adapted and from which it often recovers quickly. Drought should be distinguished from dryland degradation, which, as pointed out earlier, is brought about by inappropriate land-use practices under delicate environmental conditions.
Unlike dryland degradation, however, drought inflicts acute distress on human beings and animals, forcing mass migrations from the affected areas. Given the region's poverty and its inability to invest in new techniques, plant strains, storage facilities, and so on, the capacity to deal with drought is severely limited. As a result, many countries have become dependent on international assistance; this is especially true for small countries, but even large ones like Ethiopia (where a drought occurred in the midst of a prolonged civil war) have needed significant help. However, once normal rainfall resumes, recovery takes place quickly and people tend to return to their native areas.
Floods, on the other hand, stem from periods of heavy rainfall, either in the immediate locality or upstream of it. They are most common in river valleys and floodplains. In rural areas, their effects can be beneficial as well as harmful. Although flash floods destroy crops, livestock, and settlements, they provide ideal conditions for certain fish and for cultivating crops such as paddy rice, millet, sorghum, and vegetables. In urban areas, however, especially where there has been indiscriminate building on floodplains or where channels are blocked, floods pose real danger to life and property. In Ibadan, Nigeria, for instance, the flood of 31 August 1980 claimed about 200 lives, displaced about 5,000 persons, and damaged property worth millions of dollars.29
Insects are the most important biological hazard in sub-Saharan Africa. According to Thomas Odhiambo, the leading African entomologist, "the insect world in tropical Africa is a rich and diverse one."30 Although some species confer benefits such as pollinating trees and other plants, many others are pests to plants or serve as vectors in the transmission of disease. Serious study of insects began only recently. The initial emphasis has been on combating plant pests through heavy pesticide usewith all the deleterious environmental consequences this implies. Fortunately, most farmers in the region cannot afford to use pesticides to any great degree.
As the entomology of the region becomes better understood, there is growing appreciation of the potential for biological control of pests. The best example so far is the cassava mealybug program. Mealybugs were inadvertently introduced into sub-Saharan Africa from South America in the early 1970s. Within less than a decade, they had cut cassava yields by two-thirds in most parts of the region. However, biologists eventually found a natural enemy of the mealybug; specially bred in laboratories and distributed throughout cassava-growing areas, it has brought losses substantially under control. Thus, this program not only saved a staple on which so many people depend but also prevented major harm to the environment.
Find out more about ATF | Feature Articles | ATF Back Issues: Information You Can Use | Subscribe to ATF | Send a letter to the editor: Talk to us! | Send comments about this home page | ATF Technical Services | What's New | Related Web Sites