IISD: Report on the Intl Convention to Combat Desertification
|Arid and semi-arid lands: Characteristics and importance
Arid and semi-arid or subhumid zones are characterized by low erratic rainfall of up to 700mm per annum, periodic droughts and different associations of vegetative cover and soils. Interannual rainfall varies from 50-100% in the arid zones of the world with averages of up to 350 mm. In the semi-arid zones, interannual rainfall varies from 20-50% with averages of up to 700 mm. Regarding livelihoods systems, in general, light pastoral use is possible in arid areas and rainfed agriculture is usually not possible. In the semi-arid areas agricultural harvests are likely to be irregular, although grazing is satisfactory (Goodin & Northington, 1985).
In Africa north of the equator, arid and semi-arid zones are bordered by Senegal, Upper Volta and Chad in the south; and Morocco, Algeria, Libya, and Egypt in the north. The zones extend southeast through Somalia and Northern Kenya, South of the equator the zones cover Lesotho, parts of the Cape, Northern Transvaal and Free State provinces of South Africa; Botswana; Namibia; and parts of Zimbabwe.
The notion of desertification has been a contentious subject. UNEP's Desertification Control/Programme Activity Centre (DC/PAC) defined desertification as "land degradation in arid, semi-arid and dry sub-humid areas resulting mainly from adverse human impact", aggravated by the characteristics of dryland climates. Within the context of Agenda 21, desertification is defined as "land degradation in arid, semi-arid and dry sub-humid areas resulting from climatic variations and human activities". The difference between these definitions has to do with causation. In the former, human intervention is viewed as the central driving force in desertification; while the latter clearly identifies both human and climatic influences (Toulmin, 1993).
Another notion linked to desertification is that of desert advance. Assertions have been made that the desert is advancing at approximately 5km a year. This has been disproved by Hellden (1991) whose work in the Sudan shows no such advance and Tucker et al. (1991) who asserts that patterns of vegetative cover in these areas are dependent on rainfall. Hellden has further asserted that contrary to arguments advanced, there is no evidence that patched of desert were spreading outward from villages and water holes into the drylands of the Sahel area, for instance.
Of significance in this debate is the recognition that the majority of the population of arid and semi-arid lands depend on agriculture and pastoralism for subsistence. These zones exhibit ecological constraints which set limits to nomadic pastoralism and settled agriculture. These constraints include (Salih & Ahmed, 1993):
Indigenous peoples of these areas have lived within these constraints for centuries. They have existed on the productivity provided locally and have used their knowledge to devise coping and adaptive strategies.
In order to assist the process of efficient resource management in these fragile environments, UNEP's Global Environment Monitoring System (GEMS) and FAO's Ecological Management of Arid and Semi-Arid Rangelands (EMASAR) programmes have developed a methodology for ecological monitoring which has been applied to rangelands and planning for national parks in East Africa, and among the Fulani of Senegal in West Africa. Ecological monitoring encompasses the collection of biological and physical data at ground, air and space levels providing information on domestic and wild animal populations, human habitations and populations, vegetation production and cover, soils, land forms, climatic data and crop production. Ground level ecological monitoring also provides information on socio-economic practices of human populations which affect the ecosystem and its productivity (UNSO, 1990). Work on adaptive strategies has to focus on how this contemporary knowledge is used to reinforce or inform traditional knowledge around resource management issues.