ABSTRACT
Drought features frequently in both the written and unwritten records of the past, such as in tree rings and ice cores, but in recent years, probably because of tragic television pictures from Africa, the effects of drought seem to have become steadily more serious. In hydrological terms, most droughts are due to unexpected, unusual, and lengthy periods of little or no precipitation, which can be coupled to high levels of potential évapotranspiration resulting from high temperature, low humidity, and high wind speed. Drought and aridity should not be confused: the first is ephemeral while the second is a permanent feature and relatively easy to define. There are, how ever, some droughts that are the result of excessive use of water that causes water resources to decline, even when rainfall is near normal. Indeed, Sirculon (1991) has estimated that while the water resources of the west African Sahel may vary between ± 30-40 per cent over the next few decades, the demand for water for the same period is likely to rise by 250-500 per cent. Undoubtedly, the accelerating demand for water for drinking, cultivating crops, producing power, and other purposes, engendered by the needs of the rapidly growing population, has already been a major factor in intensifying the effects of drought in many developing countries. But increased consumption in the developed countries, sparked by the rising standard of living, has also made these countries more vulnerable. In addition, ongoing and worldwide changes to the land surface and their impacts on the hydrological regime must be taken into account. Deforestation, urbanisation, drainage of wetlands, overgrazing (leading to desertification), and other alterations to land use all cause changes to the water
balance, which may contribute to drought and exacerbate its effects, particularly on wildlife and the aquatic habitat. O f course, the rising demand for water and the adverse changes in land use have the greatest consequences for drought in the lessdeveloped countries. Warning systems there may be less effective, while the reactions to such warnings are likely to be poor because emergency services are skeletal and badly funded and infrastructures are less sound. Perhaps one hundred years ago, society in these regions was well adapted to drought, but now the increased population means that drought can be accommodated no longer. In such circumstances the development of a drought will cause greater human losses and more severe effects on society. A serious drought could even set back the development of a region or a small nation by five to ten years, and it may make the goal of sustainable development even more elusive. International and bilateral aid is rushed to areas suffering from drought to alleviate its worst
effects, often in the face of the fact that the instal lation and operation of an efficient warning system and investment in the infrastructure of the country concerned would be more effective. But even in developed countries, drought can bring problems. Water supplies are often restricted, crop production may be very low, wildfires can sweep through forested and residential areas, fisheries and wildlife will suffer, and shrinkage of clay soils may cause subsidence of buildings. These events can bring claims on insurance companies and motivate governments to provide funds to relieve the effects of the drought. In addition, drought is likely be a regional harbinger of the world water crisis that is being predicted for the middle of the twenty-first century (Postel 1992, Rodda 1995a), a time when the global demand for water may well be reaching the finite limit of the world’s water resources.
