1. Africa contains a substantial portion of the worlds arid and semi-arid rangeland, extending over three million square kilometers. These arid zones support an estimated 16-22 million pastoral population (Widstrand, 1975) and nearly 500 million head of livestock (FAO, 1975).
2. Despite their marginal productive capacity, the arid and semi-arid rangelands of the continent are highly diverse in climate, land forms, soil types and vegetation. These rangelands are characterised by their high spatial and temporal variability in precipitation which directly affects plant productivity.
3. Pastoral nomadism, the major land use of the region, is adapted to variable forage supplies and water distribution. The ability of nomadic people to survive in these marginal lands is attributed to their opportunistic mobility and diversified livestock husbandry.
4. Recurrent drought and famine are a common feature of African rangelands. This has been vividly illustrated in the Sahelian drought of 1969-1973 and the recent drought of 1983-1984 which has claimed numerous lives. Furthermore, overgrazing, sedentarisation of formerly nomadic communities, water development without sound ecological considerations, exclusion of the nomads from vital drought reserves and their compression onto smaller and more fragile land have all contributed to the deterioration of African rangelands. The people most affected by recurrent drought are the pastoral nomads. Their livestock are decimated and reports at the time of drought estimated several million livestock starving accompanied by horrifying human suffering.
5. Drought is not a new phenomenon to the pastoral nomads. Historically they have suffered numerous such disasters. Their survival can be attributed to a wide spectrum of adaptive strategies. Some of the strategies are ecologically based, while others depend upon socio-economic and cultural mechanisms. There is, however, serious concern that these drought strategies are breaking down. Today, more pastoralists are seeking outside help than ever before. This has been graphically demonstrated in Ethiopia, Somalia, Kenya and some Sahelian countries where dispossessed nomads sought survival in refugee camps, relief and urban centers (Lewis, 1975; Caldwell, 1975; Kaplan et al., 1977; Cahill, 1980; Hogg, 1983).
6. In this paper we review: (1) pastoral nomadic strategies for mitigating drought effects, including the ecological and social significance of these strategies; (2) conditions contributing to the gradual breakdown of nomadism; and (3) some current drought policies in pastoral areas. The review cannot claim to be exhaustive, but highlights the general problems faced by pastoral peoples.
7. The functioning of the ecological system is dependent on complex interrelationship between people, animal life, plants and the physical environment. Large expanses of savanna which are known to be some of the most productive ecological systems in terms of plants and animal biomass, are sustained through a dynamic balance of human activity - grazing and burning - and a broad diversity of grazing wild herbivores and predation through carnivores. Pastoral nomadism which forms part of the functioning of this ecosystem is a biological necessity for human survival in this environment.
8. The distribution of pastoral peoples of tropical Africa have been illustrated by Hans Jahnke (1982). The areas used constitute the continents arid and semi-arid rangelands. In these eco-climatic zones, the rainy season varies from a few weeks to three to four months (Le Houerou, 1980); growing time of forage plants varies from less than 90 days in northern fringes of the Sahara to 180 days in the Savanna Zone (Wallen and Gwynne, 1978; Jahnke 1982). Potential evapotranspiration is extremely high: 1500 to 2500mm per year, in some places almost always exceeding actual rainfall (Berry1975; Gallais and Sedikou 1978). Such high evapotranspiration demands result in moisture deficits which drastically reduce duration of plant growth and therefore green forage availability.
9. Furthermore, rainfall variability, both in space and time, causes uneven and unpredictable levels of forage productivity (Le Houerou and Host, 1977; Herlocker and Dolan, 1980; Lamprey and Yusuf 1981). For example, in northern Kenya, during the drought years of 1968 to 1976, mean annual rainfall was approximately 50mm. In contrast, rainfall In 1977 was over 350mm, which was reflected in greatly increased plant production (Lamprey and Yusuf, 1981). Even more important is the spatial distribution of rainfall, especially in the rangelands of East Africa, where rainfall is produced by individual storms (Wallen and Gwynne, 1978). This has important influence on how the range resources are used by nomads.
10. Recurrent drought is a common problem in African rangelands. The areas most susceptible to drought problems are those which are subject to erratic seasonal variation in precipitation. Drought on these rangeland reduces forage production and water supplies, placing serious pressure on the livestock industry. The pastoral nomads have evolved numerous adaptive strategies which ensure their survival. These strategies are reviewed briefly below, as a backdrop for an analysis of the reasons why some are no longer effective