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Precipitation is scarce and has a high annual variance in dryland areas. Very high daily temperature variance is recorded with frequent sand storms, dust ghost, and intense sunshine. Arid plants usually belong to drought escaper, drought evader, drought resister, or drought endurer categories. Evaporative losses and water limitations are the most prominent factors dictating animal life in arid environments. Low rainfall dictates the formation of shallow or extremely sallow soils that often are characterized by high content of airborne particles and small fractions of rock-erosion elements. Most of the soils are poor in or completely devoid of organic matter, and the nutrient pools of the soils are low. Apparently, humans not only utilize the ecosystem services of this region but are also influencing the evolution of some of its important biotic elements. In Mongolia, for example, while soil fertility has decreased by about 20% in the past 40 years, about one-third of the pasturage has been overgrazed and 5 Mha of arid land have constantly been threatened by moving sands (Khuldorj et al., 1998). Soils exposed to degradation as a result of poor land management could become infertile as a result of climate change. Temperature increases would have negative impacts on natural vegetation in desert zones. Plants with surface root systems, which utilize mostly precipitation moisture, will be vulnerable. Climate change also would have negative impacts on sheep breeding and lamb wool productivity.
Just as shifts in vegetation belts are expected in non-drylands, in the drylands of Asia a shift in dryland types is expected as a result of climate change. Drylands are ranked along an aridity index, in relation to the ratio of precipitation to potential evapotranspiration (i.e., to a gradient in soil moisture available for driving production). Because soil moisture is likely to decline in this region, the least-dry land type (dry subhumid drylands) are expected to become semi-arid, and semi-arid land is expected to become arid. It is notable that population pressure on dryland resources is reduced with increasing aridity, but resistance to degradation and resilience following degradation also is reduced with increasing aridity. Therefore, semi-arid drylands, which are intermediate in aridity as compared to arid drylands and dry subhumid ones, are most susceptible to becoming further desertified (Safriel, 1995). Because semi-arid drylands are very common among Asian drylands, large areas will become not only dry but also desertified as a result of climate change,.
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