Desertification is global. Two-third of the world's 150 nations are affected by desertification


By Dr. S.M. ALAM, NIA, Tando Jam.
Jan 06 - 12, 2003



Desertification is an interplay of natural and cultural processes working singly or in combination leading to encroachment or acceleration of desert conditions in arid and semi-arid areas of their margins. Desertification occurs in the arid and semi-arid regions of the world. It is not so much that the deserts are advancing by themselves, but that man, by his actions, is putting them out. The world has five main desert zones, which largely lie in two belts of latitudes 15 and 30 degrees both north and south of Equator. i) The Sonoran Desert of NW Mexico and its continuation in the desert basins of the SW United States of America, ii) The Atacama Desert, a thin coastal strip between the Andes and the Pacific Ocean, running from southern Ecuador to central Chile in South America, iii) The great belt of desert running from the Atlantic Ocean to China and including the Sahara Desert, the Arabian Desert, and desert of Iran and USSR, the Rajasthan Desert of India and Pakistan, and the Takla-Makan and Gobi Deserts in Western China and Mongolia.

Desertification occurs not in these natural deserts, but in the arid lands (200250 mm; 8-10 inches of rain per annum) and semi-arid lands (250-600 mm; 10-23 inches), that are nearby. One third of the Earth's land surface (47 million sq. km or 18 million sq. miles) is arid or semi-arid. This is the home of more than 600 million people - one-seventh of the human population. More than half of this area, 30 million sq. km (or 12 million sq. miles) or more than 20 % of the Earth's surface is under direct threat of desertification. Eighty million people live on this threatened land. Desertification is global. Two-third of the world's 150 nations are affected by desertification. Of the 30 million sq. km (or 12 million sq. miles) of land, which UNO has estimated was threatened by severe desertification.



The UNO has estimated that desertification on the fringes of the Sahara is spreading at 1.5 million hectares (3.7 million acres) each year. Every 10 years, an area the size of Czech and Slovak is being turned into waste land Man's hunger for food is destroying the very land upon which that food must be grow UNO estimated that the world will lose one-third of its arable lands through desertification by the end of the century. Yet food production must be increased by one-third over the same period to feed the growing population. Desertification has four primary causes: over cultivation, overgrazing, deforestation and poor irrigation practices. These are highly influenced by three contributing factors. Population changes, climatic changes and changing social and economic conditions of a country. In Pakistan, deforestation, overgrazing and misuse of land has contributed to on set of desertified conditions in the Thar,` Cholistan, Coastal Makran, and western border areas. Once the resource base is depleted in such fragile lands, it is very difficult to bring it back for productivity. About 40 per cent of the total land area is desert, comprising Balochistan, and Thar desert, the Thal and Coastal desert of Makran. High human and livestock population, intensive overgrazing of range lands, cutting of trees and forests, mining, over pumping of groundwater, indiscriminate hunting of wildlife, are some of the cultural practices that have been causing accelerated soil erosion by wind and water.

Over cultivation: In recent years, traditional rainfed cropping, systems have been breaking down, in many places in the world. Rapid population growth has created a demand for more food production. The increase in the area under rainfed cropping has occurred at the expense of marginal lands, which have traditionally been used for livestock. The cultivation of these less productive and more drought-prone lands, together with diminishing returns from lands under shorter follows have resulted in a decrease in average crop yields per hectare. Over cultivation of marginal lands with the consequent crowding of increasing numbers of livestock into smaller areas of pasture has caused both crops and livestock productivity to fall and soil erosion to increase. Populations are growing rapidly, making desertification more acute. Drought phenomenon triggers off a crisis, but does not itself cause desertification, which usually arises as a result of a combination of two or more of the primary causes acting together. Livestock density has gone up and so the pressure on the land has increased due to their overgrazing.

Overgrazing: Overgrazing is indeed a major cause of desertification. Overgrazing can lead to a decline in palatable grass species, particularly perennials, which are also good at holding the soil together. A decline in the health of livestock and a fall in the production of milk and meat.

Irrigation: Irrigation can lead to a six-fold increase in the yields of cereals and up to five-fold increases for root crops. Some 250 million hectares (618 million acres) of irrigated farmlands exist at present, accounting for about 13 % of all land under cultivation in the world. As well as improving yields, irrigation can remove arid lands susceptibility to crop failure during droughts. Irrigation also means big money for construction and other companies in developing and developed nations. If irrigation water cannot drain off, the soil becomes water logged and salts are not leached away. Water logged soil is itself difficult to cultivate. When the dry season comes, high temperatures encourage evaporation of water from the soil. Water logging of land in the Indus Basin is a consequence of irrigation developments in an otherwise arid and semi-arid land without provision for adequate drainage of land are flushing of saline effluents from the soil. Seasonal rise of water table leaves salts behind affecting crop productivity and yields.