Wind erosion in Africa and West Asia :problems and control strategies : proceedings of the expert group meeting, 22-25 April 1997, Cairo, Egypt

Drylands are important sources of aeolian particles (dust and other particulates) associated with a variety of human activities, including vegetation removal and biomass burning. A wide range of empirical and numerical modeling studies, which relate climatic variation in drylands to a variety of forcing mechanisms, has established the strength of the link between the global climate system and specific climate patterns in the dryland areas. Wind erosion, the removal of soil by wind, is one of the most damaging effects of wind in many parts of the world. As a rule, it only assumes the status of a major problem in regions with a strongly-marked annual dry season, and hence is a potential hazard in all dry environments. Much of the early work on wind erosion was carried out in the great plains of the United ·states, the wheat fields of the Canadian prairies, and the south of the former USSR. The problem has also been studied in Europe, Asia, and Australia. The occurrence of wind erosion is a function of weather events interacting with soil (intrinsic properties) and land management (past and present practices) through its effect on soil structure, tilth, and vegetation cover. As with water erosion, most wind erosion damage comes from relatively rare, severe events. Increased availability of simple and inexpensive "sand catchers" and automatic weather stations over the past 5- 10 years makes the task of monitoring sand flux and weather data easier. Wind erosion presents multiple challenges: identifying where wind erosion is most threatening to sustainable agricultural productivity; what practicable farmer-friendly measures can be devised to contain it; and how these measures can be transferred (for instance, through extension services) and implemented within agricultural land-use systems. According to previous studies, wind erosion in the semi-arid regions of America, North and South Africa, Australia, the Near East, and many parts of Central Asia only reached threatening proportions when man disturbed the ecosystem balance. This is true for West and Central Africa (WCA), and West Asia and North Africa (W ANA), where growing population pressures have led to the replacement of the traditional practice of fallowing with slash and burn practices and continuous cultivation. In regions (WCA and some parts of (WANA) where little or no nutrient amendments are made to replace the rapidly declining soil nutrient pool, the soil cover is declining rapidly, leading to wind erosion and land degradation. In WCA, where wind erosion is usually severe during the beginning of the growing season, young crops are damaged by wind-blown sand, leading to problems of poor crop stand and yield decline. Wind erosion in arable fields and rangeland causes various losses of soil depth, organic matter, clay content, nutrients, and indigenous seed. Downstream effects, e.g., effects, e.g., increased atmospheric dust, reduced visibility, blockage of roads, railway lines, problems of health, etc., are also causing considerable concern. In Morocco, seasonal hot winds not only carry away soil but also affect crop performance through excessive evapotranspiration and direct wind effects. In the oases, sand encroachment affects wells, palm tree plantations, and traditional irrigation systems. In the southern and southwestern parts of Tunisia, the movement of sand dunes poses a major threat to farmlands. In much of West Asia and North Africa, large areas of the traditional semi-nomadic rangeland, the steppe, are being opened for barley cultivation. The consequent removal of the natural vegetation cover has exposed the soil surface, leading to the loss of the fertile fine fraction of the shallow soils through wind erosion. This has led to a tremendous decline in soil productivity and quality of life. Hence, the Government of Syria, for example, has forbidden the conversion of the steppe for barley cultivation.

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