According to the UNEP data, in the past 50 years, 36 countries in Africa have been exposed to the land degradation of dry lands, namely desertification. The dry lands in the world occupies 40 percent of the world’s total, covering an area of about 5.1 billion ha and making the resources affected seriously, on which more than 1 billion people rely for survival and living. Desertification has affected 70 percent of the dry lands, that is to say, the land with an area of 3.6 billion ha, or one fourth of the world’s land, has been affected by desertification. The estimate available shows that desertification has occurred on 30 percent of the irrigated agricultural lands, 47 percent of the rain-fed agricultural lands and 73 percent of the pastures in the world.
The decrease of the annual income caused by desertification is up to 42 billion dollars every year in the worldwide. And the ecological refugees or decreased crops caused by desertification have inflicted indirect social and economic losses to the surrounding zones as well. 2.5 billion people are influenced directly by desertification, and other about 1 billion people are confronted with the threaten of desertification. These people include the most seriously poverty-stricken population in the world. If we don’t take measures for prevention before 2050 year, economic losses will increase sharply and 1.8 billion people will be impacted on. The consumption of restoration of the land suffering desertification will be far more than the input of prevention.
It is thought in “the study of the world’s sand sea”, which is under the general editorship of Edwin D. Mckee, that desertification is one of the main types of land degradation in the dry areas, with Aeolian sand appearing on the land surface as one of the main indications. The Aeolian sand distributed in the arid desert areas is generally called desert or sand sea. The inland Aeolian sand distributed in the semi-arid and humid areas is often named sandy waste or sandy land. The global desert area accounts for 23.3 percent of the total area of semi-desert and desert in the world, and it is about 7 million square kilometers.
There is no great desert distributed continuously in the desert areas of southwestern United States, and just Aeolian sands scatter there, which cover an area of 170,000 square kilometers. They are often assigned names with dune or sand, such as White Sands and Algodoness Dunes. The sands along the lakes and the coastal sands in the grassland areas of central United States cover an area of nearly 1 million square kilometers.
The Sahara deserts in North Africa, with a total area of 9 million square killometers, are the largest deserts in the world, each desert of which is not the biggest one though. The deserts separated by Gobi and rock desert cover an area of 1.8 million square kilometers, making up 25.7 percent of the total desert area in the world, some of which are of larger areas, and they are the Eastern Desert (192,000 square kilometers), the Western Desert (103,000 square kilometers) and the Zook Desert (58,000 square kilometers).
The southwestern Kalahari Desert in South Africa occupies an area of 110,500 square kilometers, and the area of lowland desert in Kalahari is 1,613,800 square kilometers. Namib Desert covers an area of 34,000 square meters.
Asia has larger deserts, which are about 250 square kilometers in size. Among these deserts, the desert of the Arabian Peninsula covers an area of up to 795,000 square kilometers. The area of Rub’ al Khali Desert is 560,000 square kilometers, which can be named the biggest desert in the world. The area of An Nafud is 73,000 square kilometers and the area of the Wahiba desert is 16,000 square meters. Besides, there are small deserts like Dahena Desert and Nefud Desert.
The deserts in Central Asian U.S.S.R, Kazakhstan and the North Caspian Sea cover an area of 830,000 square kilometers.
The Mongolia Desert covers an area of about 520,000 square kilometers, most of which are gravel Gobi, and the scattering dunes cover an area of about 15,000 square kilometers.
The Iranian deserts are not deserts but salt deserts, the Carville Salt Desert of which covers an area of 47,000 square kilometers and the Lute Salt Desert covers an area of 52,000 square kilometers. The flowing dunes scatter around the salt deserts and on the plateaus, covering an area of 50,000 square kilometers.
The Thar Desert in India and Pakistan covers an area of 260,000 square kilometers.
The total area of the deserts in Australia is 1.05 million square kilometers, the Simpson Desert of which occupies 312,000 square kilometers, the Gibson Desert covers 221,000 square kilometers and the Great Sandy Desert covers 360,000 square kilometers.
The mobile deserts in the globe are mainly distributed in Africa, Arabian Peninsula and Northwest China and scatter in other areas, the area estimated of which is 4.5 million square kilometers, accounting for 64.3 percent of the world’s total deserts. The annual precipitation is less than 100 mm. The dunes are tall and dense. These areas are sparsely populated. Neither the economic nor the natural conditions are available for the vegetative sand control. Vegetative sand control is limited to preventing the new and old oasis, industrial mines and transportation, and residents’ communities in the towns.
The fixed and semi-fixed deserts in the world, with precipitation of over 100 millimeters, are about 2.5 million square kilometers in size, taking up 35.7% of the world’s total deserts. They are mainly distributed in South Africa, Central Asia, Thar Desert, Australia and the Gurbantunggut Desert, and the Qaidam Basin in our country. They are relevant to the monsoon rain, the Mediterranean and plateau climate. The appearance of mottled and strap-shaped quicksand and banded quicksand is always associated with the vandalism of sandy vegetation.