In semi-arid and arid environments, rainfall is short-lived and often very intense. Because soils tend to be thin, much of the rainfall runs directly off of the surface, only to infiltrate deeper soils downslope or along river beds (IPCC 1996, WG II, Section 10.2.1). Thus, water availability is a major concern in most countries of the region (Middle East Water Commission, 1995; UNEP, 1997). Some countries (e.g., Syria, Iraq, Jordan, Lebanon) have reliable sources of surface water; the majority, however, depend either on groundwater or on desalinization for their water supply-both of which enable them to use water in amounts far exceeding the estimated renewable fresh water in the country (World Bank, 1995c; IPCC 1996, WG II, Chapter 4; GEO, 1997). Wetlands can retain water, especially during dry periods, and thus can enhance recharge to major aquifers (IPCC 1996, WG II, Section 18.104.22.168.3). However, in semi-arid and arid areas, where groundwater recharge occurs after flood events, changes in the frequency and magnitude of rainfall events will alter the number of recharge events (IPCC 1996, WG II, Section 10.3.6). Water from glacial melt is an important contribution to the flow of some river systems, and changes in seasonality and amount from this source are likely to occur as a result of climate change (see Section 22.214.171.124). Fossil aquifers are important water sources in many deserts; they will not be affected on a time scale relevant to humans (IPCC 1996, WG II, Chapter 3).
As a result of rapid increases in the income of some countries-with resulting increases in living standards-the demand for water has increased, such that many countries in the Middle East will experience chronic water shortages (IPCC 1996, WG II, Section 14.2.2; UNEP 1997). The list of nations with water supply problems is likely to expand as a consequence of the accelerated pace of urbanization. In some countries (e.g., Kuwait), monitoring programs for water quality have been established in an attempt to maintain water quality in accordance with World Health Organization (WHO) standards (UNEP, 1997). It is projected that the population without safe drinking water will almost double by 2030, assuming a "business-as-usual" scenario (IPCC 1996, WG II, Section 14.2.2).
Many countries in the region have highly urbanized populations, for whom it is easier and more efficient to organize water supply, treatment, and delivery systems than it is for rural populations. Moreover, demand can be more easily managed to promote water-use efficiency in urban areas. In most countries in the region, a large proportion of the population has running water in their homes. Although municipal and industrial water use will grow, per capita domestic use is likely to decrease and the quality of drinking water to increase with centralized treatment. However, future urban water demands are likely to compete with the irrigated agricultural sector (IPCC 1996, WG II, Section 14.2.2); 15 of the countries in the region use more than 75% of their water for irrigation (see Table 7-1).
There are other problems associated with some water bodies in the region, especially in areas of high human density. In these areas, habitat degradation often is important, causing many semi-enclosed water bodies to become eutrophic (Kharin, 1995; IPCC 1996, WG II, Section 16.1.1). Dryland salinization also is having an impact on water quality in some countries where groundwater is contaminated with salt; in other countries (e.g., Oman and United Arab Emirates), seawater has intruded into freshwater aquifers (UNEP, 1997).
Efforts are being made in some countries to use wastewater (Sarikaya and Eroglu, 1993; Abdelrahman and Alajmi, 1994; Shelef et al., 1994; Shelef and Azov, 1996)-and to use water more efficiently, especially for agriculture. The Middle East Water Commission (1995) suggests that, for some countries, a reduction of 30% in water use for agriculture would alleviate some water crises. Increased recycling of water is being explored in areas where there are shortages of water, either perennially (e.g., Israel and Oman) or during some seasons (e.g., Turkey in the summer, when shortages are exacerbated by tourist demand) (Middle East Water Commission, 1995; IPCC 1996, WG II, Section 14.2.2). In many of the countries of the FSU, plans are underway to increase the efficiency of irrigation practices, with savings of over 20% expected in some regions (see Section 7.4.1).
Populations in many countries of the region are vulnerable because they depend on water supplies from outside their political boundaries. Formal agreements are in place, or are being developed, to share the water resources of rivers flowing across political boundaries (e.g., Euphrates, Tigris, Jordan, and Indus); such agreements would reduce the potential for future conflicts over water (Blaikie et al., 1994; Middle East Water Commission, 1995).
River-basin runoff is very sensitive to small variations in climatic conditions and in the vegetation cover of its catchment. Riebsame et al. (1995) used two GCMs (GISS and GFDL) to assess the effect of climate change on various rivers throughout the world, including the Indus. The GCM climate scenarios projected an increase of 11-16% in annual runoff for the Indus. The authors also assessed the effect of a 2�C temperature increase with +20%, 0%, and -20% changes in precipitation and found that runoff is more sensitive to changes in precipitation than to changes in temperature.
The effect of climate change on runoff has been studied for some river basins in the region. Based on two GCM runs (CCC-J1 and GFDL-A3) with 2xCO2 equilibrium climate scenarios, several mountain and plains watersheds experienced 30-35% reductions in runoff in years of water shortages and 20-25% reductions in years of excess water. A projection based on a third GCM run (GFDL-X2g transient model) confirms the tendency for a reduction in water resources during years of plentiful water supply for mountainous watersheds (Pilifosova et al., 1996). In the short term, however, some studies suggest increases in water resources. For example, the above simulation projects increases of up to 12% in the water resources of some watersheds in 2000 and 2030 (Golubtsov et al., 1996).
Some countries in the region produce large amounts of hydropower; Tajikistan, for example, is the third-highest producer in the world (World Bank, 1995b). Changes in runoff to the system could have a significant effect on the power output of these countries. One of the bigger river systems in the region, the Euphrates and Tigris, has a number of dams that are used for irrigation and water supply as well as for hydropower. To date, no studies have assessed the effect of climate change on these systems. However, if there is a reduction in total runoff as a result of climate change, the increased demand for agricultural and hydropower activities could place more pressure on water resources.
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