Historical and Current Perspectives of AKST | 39

structure is the sand storage dam, which is a sand-filled reservoir watered by the wadi flow.

2.1.4.4 Irrigation infrastructures

Irrigation covers about 48 million hectares in CWANA. Central Asia represents 59% of this total, although it covers only 21% of the total area. Pakistan alone, covering a little over 4% of the region, accounts for 33% of the irrigated areas. By adding Egypt, Iran, Iraq and Turkey, 72% of the land under irrigation is controlled by five countries in CWANA. Surface irrigation is by far the most widely used technique, practiced on 88% of the area. Sprinkler irrigation is practiced on 11% and microirrigation on 1.4% of the total area. In Libya and Saudi Arabia, sprinkler irrigation is clearly predominant, while in Jordan, Oman and the United Arab Emirates, microirrigation is most widely used. It is practiced on over half of the full and partial control irrigation areas (AQUASTAT, 2002). In Kuwait and Lebanon, sprinkler irrigation is used on more than 37% and microirrigation 39% of their full and partial control irrigation areas. The arid countries without large rivers choose to develop more intensively microirrigation and sprinkler irrigation to save water (AQUASTAT, 2002).

CWANA is subject to salinization because the volume of rainwater dissolving the salts generated by the soil is low. The problem has long been recognized; however, national assessment of salinization is difficult and little information on it can be found. Furthermore, no commonly agreed upon methods exist to assess the degree of irrigation-induced salinization. More information on salinization will probably become available. Strategies to improve the situation, recognized as a priority by most CWANA countries, should be defined. All countries reported having salinization problems, varying from 3.5% in Jordan to over 85% in Kuwait.

A measure necessary to prevent irrigation-induced waterlogging and salinization in arid and semiarid regions is installing drainage facilities. Drainage, in combination with adequate irrigation scheduling, allows leaching of excess salts from the plant root zone. Figures on drained areas are available for 13 of the CWANA countries in the FAO AQUASTAT database (2002). About 34% of these irrigated areas have been provided with drainage facilities, varying from 0.6% in Iran to over 90% in Egypt.

2.1.5 Land degradation and water quality deterioration

The degradation of arable land resources is as old as the history of irrigation and human settlement. A well-documented case occurred between 4000 and 2000 BCE, within the boundaries of CWANA, where secondary salinity affected the land and water in the Tigris and Euphrates valleys in Mesopotamia. History has repeated itself in the last century in many other countries of the region.

Water-quality deterioration, recognized as a global problem, has been exacerbated in dry regions. Research on water-quality deterioration began later than research on land degradation in CWANA, where problems from water-quality deterioration are expected to intensify, due to anthropogenic interventions and the increasing possibility of extreme events of climate change (IPCC, 1998, 2007).

 

In addition, saline water intrusion is expected to increase, from sea level rise and overexploitation of groundwater in coastal zones. Salt-prone water and land problems are expected to increase in arid and semiarid regions (Qadir, Wichelns et al., 2007). Declining water quality has also increased water supply problems, especially in drier climates. Pollutants have a greater opportunity to accumulate during dry periods. A heavy reliance on irrigation in some areas has compounded the problem (UNEP, 2002). Research long focused more on water quantity and use than on its quality. Since the 1980s, there has been increased attention on the productivity of irrigated agriculture and conservation of the environment.

2.1.5.1 Land degradation

Processes and causes of land degradation have been studied since the beginning of the twentieth century. Land degradation remains important for the twenty-first century because it adversely affects agronomic productivity, the environment, food security and quality of life. Land quality declines. According to the Global Assessment of Human Induced Soil Degradation (GLASOD) (Oldeman, 1988), land degradation is linked to climate variation and unsustainable human activities, such as overgrazing, deforestation and poor agricultural practices (Bossio et al., 2007). Land degradation is also linked to population density (Roose, 1996); in an agrarian system, if the population passes a certain threshold, land starts to run short and soil restoration mechanisms seize up. In some dry zones, when the population reaches about 100 inhabitants per square kilometer, the zone is rated as a densely populated, degraded area. A rapidly growing population and limited land resources mean that combating desertification will be difficult for developing and poor countries.

The Global Assessment of Soil Degradation is the first baseline study using a consistent methodology to estimate global soil degradation (Oldeman, 1988). Its estimates of the extent of affected areas are rough and should not be used as precise data (Table 2-2). However, they provide a good overview of the situation. National authorities concerned with land degradation need to update and refine present estimates and mapping. Major soil constraints and vulnerability for CWANA countries are related to sodicity, shallowness and erosion risk. Erosion risk is major, affecting 5% of Central Asia and the Caucasus and 20% of South Asia and West Asia (Table 2-3) (Nasr, 1999). Mechanisms that start land degradation are numerous (Bossio et al., 2007). A decline in soil structure causes crusting and compaction, leading to decreased infiltration rates and increased erosion. Significant chemical processes include acidification, salinization, pollution and fertility depletion. These processes can operate individually, simultaneously or in combination and threaten the sustainability of natural resources.

The salinization of land in CWANA is the consequence of both naturally occurring phenomena and human activities. Anthropogenic activities contribute more to salinization of land and water resources than primary salinity. Excessive irrigation, accompanied by inefficient drainage (Qadir and Schubert, 2002) caused by either lack of information on crop water requirements or a need to apply leaching water,