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From?Vol. XLIV, No. 2, "Green Our World!",? June 2007

The Arab region is comprised of 21 countries, extending from North Africa to South West Asia, over an estimated total area of 14.1 million square kilometres. Its vast terrain includes physiographic features of plains, plateaus, dry valleys and relatively limited highlands and mountainous areas.

Countries of the region are distinguished by vast coastal areas overlooking segments of the Arabian Gulf, the Arabian sea, the Red Sea, the Mediterranean Sea and the Atlantic Ocean. The region's population is expected to reach over 290 million by 2010, with a continued growth rate estimated at an average of 2 per cent per annum.

Aridity is the main climatic feature of the Arab region, and hyper-arid or arid conditions prevail in over 89 per cent of the area, while the remaining 11 per cent of semi-arid and limited sub-humid areas are confined to elevated lands. Marginal rainfall of up to 350 millimetres per year extends over the arid areas, while semi-arid zones experience between 400 and 800 mm/year and sub-humid areas between 800 and 1,500 mm/year. However, rainfall throughout the region is characterized by rapid changes in spacial distribution, seasonal variation, inter-annual variability, varied intensities of sporadic showers and changing lengths of the growing season. Most Arab countries experience highly variable rainfalls and recurrent drought spells of varied severity and length. Such high variabilities extend to average annual temperatures, as well as maximum and minimum temperatures, varying from freezing to a high of over 50? Celsius, depending on the season and location.

These data clearly demonstrate the significant impact of climatic features on land-use categories and the productivity of each category, with special reference to rangelands, rain-fed cultivated areas and the degradation processes in the region. Among the most influential climatic factors is rainfall. The total amount of rainwater received in the Arab region is estimated at 2,282 billion m3/year, compared to an estimated 205 billion m3/year for surface water and 35 billion m3/year for groundwater. This clearly shows that the mostly marginal rainfall in the region represents the major water resource available, despite the constraints facing water efficiency. As a result, national country reports clearly show that a major fraction of the rainwater received is lost through the combination of evapotranspiration, seepage, run-off and flash floods through uncultivated wadies reaching lakes and marine coastal areas. Recurrent drought spells have definite adverse impacts on productivity of agro-ecological zones, resulting in large economic losses and negative impacts on social development.

The potential climate change scenarios are becoming real threats, according to the Intergovernmental Panel on Climate Change (IPCC). Elevated evapotranspiration and increased heat stress could lead to enhanced water requirements of growing crops. The impacts on pests and plant diseases, in addition to the possible changes in rainfall patterns, could also be significant. Ocean- and sea-level rise could lead to inundation of the lengthy coastal areas of the Arab region that could result in loss of productivity, salt-water intrusion, loss of valuable biodiversity of wetlands, salinization of groundwater aquifers and migration of the population living in the affected areas. In addition to the direct impacts of climate changes, geomorphological features and human-induced factors combine to cause serious land degradation processes as depicted in the following:

Wind erosion. The processes of wind erosion, mobile sand dunes and sand encroachment are active in all countries of the Arab region. The areas affected, along with the rate and the magnitude of the adverse environmental impacts of such processes, vary from one country to another. Wind erosion is one of the major factors of land degradation, both at the national and regional levels.

Significant areas of most countries in the Arabian Peninsula and northern Africa are covered by sand drifts: in Saudi Arabia 2.2 million km2; 90 per cent of the total area of the United Arab Emirates; almost all of Kuwait; most of the western desert of Egypt (more than 26 per cent of the total area); and several zones in the Sudan and southern Morocco. Other countries are affected to varied extents. The complex aerodynamics of wind movement and the prevailing microclimate affect the sand drifts' morphology and movement. Large amounts of sand encroachment occur during the dry summer months (June to August). Direction of the sand movement comes from the main wind direction, from north and northwest, which accounts for more than 70 per cent of the total drift movement. However, during strong monsoon winds, drift movement occasionally occurs from southeast to northwest.

The problem of sand drifting is due to climatic factors, combined with geological aspects of soil attributes and human-induced factors, including deforestation, overgrazing and misuse of land resources, which lead to degradation of natural plant cover. In turn, this enhances the susceptibility of the barren soil to erosional processes by wind and water. Moreover, military operations in wars and conflicts cause considerable changes in surface features, which stimulate deflation, abrasion and drift migration. The adverse environmental and land degradation impacts of sand encroachment and mobile dunes include encroachment on productive agricultural lands, leading to marked lowering of productivity and loss of top soil layers of higher fertility and soil nutrients. Wind drifts cause serious constraints to infrastructure and adverse impacts on health and social activities.

Water erosion. National reports of more than 10 Arab countries, including Algeria, Egypt, Lebanon, Libya, Morocco, Oman, the Sudan and Syria, point out that, despite prevailing aridity at varied degrees, water erosion is still one of the main factors of land degradation. Physiographic features, with heavy showers and sporadic torrential rain of short durations, typical of rainfall variabilities in the region, and degradation of natural vegetative cover due to human mismanagement of land resources, all combine to develop varied rates of soil water erosion. In many cases, such processes lead to serious loss of top soil materials that cause significant adverse impacts onsite and offsite. Soil water erosion also causes dam reservoirs siltation and soil loss to marine and coastal areas, leading to serious environmental and economic consequences. The combined attributes of climatic factors, physiographic features and rainfall characteristics are fundamental for the implementation of water harvesting techniques in the region. Appropriate water harvesting techniques are imperative to support the water supply during the short rainy season, as well as for supplemental irrigation of shrubs and trees in the dry months.

Flash floods. Another example of the combined effect of climatic factors and physiographic features is the formation of serious floods during the rainy season. Despite the low rate of rainfall, expanded areas of watersheds lead to the collection and formation of floods, gushing with vigour and high velocity through wadies or dry areas, causing damage to installations, infrastructure and farmlands. A clear example is the flash flood that occur in Sinai, Egypt, where watersheds of extended areas and an annual average rainfall of only 50 mm collect serious floods and follow slope patterns to the Gulf of Suez or the Gulf of Aqaba.

Climatic features in the Arab region, either through direct impacts or interactions with other factors, including physiographic features, soil attributes, level of vegetative cover and human-induced factors, lead to several processes that are highly interrelated with land degradation and its adverse impacts in the region. At present, all Arab countries engage in national and regional activities to combat such processes and alleviate their consequences.

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