THAR DESERT

also called Great Indian Desert, a tract of rolling sand hills located partly in the Indian state of Rajasthan and partly in Pakistan. Covering 77,000 square miles (200,000 square km) of territory, it is bordered by the irrigated Indus plain to the west, the Aravalli Range to the southeast, the Rann of Kutch to the south, and the Punjab plain to the north and northeast. The desert results from the dryness of the prevailing monsoon winds, which do not bring sufficient rain to keep the region moist. The name Thar is derived from t'hul, the general term for the region's sand ridges. The desert sands cover early Precambrian gneiss (granitelike metamorphic rocks formed in the oldest geologic era, which began 3.8 billion years ago), sedimentary rocks from about 2.5 billion to 570 million years old, and more recent material deposited by rivers (alluvium). The surface sand is aeolian (wind-deposited) sand of the Quaternary Period (the most recent geologic period, which began about 1.6 million years ago). The desert presents an undulating surface, with high and low sand dunes separated by sandy plains and low, barren hills, or bhakars, which rise abruptly from the surrounding plains. The dunes are in continual motion and take on varying shapes and sizes. Older dunes, however, are in a semistabilized or stabilized condition, and many rise to a height of almost 500 feet (150 m). Several playas (saline lakes), locally known as dhands, are scattered throughout the region. The soils consist of seven main groupsdesert soils, red desertic soils, sierozems (brownish gray soils), the red and yellow soils of the foothills, the saline soils of the depressions, and the lithosols (shallow, weathered soils) and regosols (soft, loose soils) found in the hills. All these soils are predominantly coarse-textured, well-drained, and calcareous (calcium-bearing). A thick accumulation of lime often occurs at varying depths. The soils are generally infertile and, because of severe wind erosion, are overblown with sand. The amount of annual rainfall in the desert tract is generally low, ranging from about 4 inches (100 mm) or less in the west to about 20 inches (500 mm) in the east. Precipitation is highly erratic, and there are wide fluctuations in the amount from year to year. About 90 percent of the total annual rain occurs during the season of the southwest monsoon, from July to September. At other seasons the wind blows from the northeast. May and June are the hottest months of the year, with temperatures rising to 122 F (50 C). During January, the coldest month, the mean minimum temperature ranges between 41 and 50 F (5 and 10 C), and frost is frequent. Dust storms and dust-raising winds, often blowing with velocities of 87 to 93 miles per hour (140 to 150 km per hour), are common in May and June. The desert vegetation is mostly herbaceous, or of stunted scrub; trees occasionally dot the landscape. On the hills, gum arabic acacia and euphorbia may be found. The khajri (Prosopis cineraria) tree grows throughout the plains. The thinly populated grasslands support the black buck, the chikara (gazelle), and some feathered game, notably the francolin and quail. Among the migratory birds, sand grouse, ducks, and geese are common. The desert is also the home of the vanishing great bustard. There are five major breeds of cattle in the Thar tract. Among these, the Tharparkar breed is the highest milk yielder, while the Kankre breed is good both as a beast of burden and as a milk producer. Sheep are bred for both medium-fine and rough wool. The camel is commonly used for transport, as well as for plowing the land and other agricultural purposes. Most of the inhabitants reside in rural areas and are distributed in varying densities. Customs, rituals, and modes of dress are manifold. Both Islam and Hinduism are practiced, and the population is divided into complex economic and social groups. Many nomads are engaged in animal husbandry, crafts, or trade. They do not belong to a specific ethnic group, nor are they associated with a separate area; in general they are symbiotically related to the sedentary population and its economy. The grasses form the main natural resources of the desert. They provide nutritive and palatable pasturage, as well as medicines used locally by the inhabitants. Alkaloids, used for making medicine, and oils for making soap are also extracted. Water is very scarce. Whatever seasonal rain falls is collected in tanks and reservoirs and is used for drinking and domestic purposes. Most groundwater cannot be utilized because it lies deep underground and is often saline. Good aquifers have been detected in the central part of the desert. Apart from wells and tanks, canals are the main sources of water throughout the desert. When water is available, crops such as wheat and cotton are grown. The Sukkur (Lloyd) Barrage on the Indus River, completed in 1932, irrigates the southern Thar region in Pakistan by means of canals, while the Gang Canal brings water from the Sutlej River to part of the northern region. The Rajasthan Canal irrigates a vast amount of land in that part of the Thar region in India. The canal begins at the Harike Barrageat the confluence of the Sutlej and B eas rivers in the Indian Punjaband continues in a southwesterly direction for 292 miles (470 km). Thermal-power-generating plants, fueled by coal and oil, are located only in the large towns and supply power only locally. Hydroelectric power is supplied by the Nangal power plant located on the Sutlej River in Punjab. Roads and railways are few. One railway line serves the southern part of the region. In the Indian part of the desert, a second line goes from Merta Road to Suratgarh via Bikaner, while another connects the towns of Jodhpur and Jaisalmer. In the Pakistani part of the desert, another railway line runs between Bahawalpur and Hyderabad. The partition of India and Pakistan in 1947 left most of the irrigation canals fed by the rivers of the Indus system in Pakistani territory, while a large desert region remained unirrigated on the Indian side of the border. The Indus Water Treaty of 1960 fixed and delimited the rights and obligations of both countries concerning the use of waters of the Indus River system. Under the agreement, waters of the Ravi, Beas, and Sutlej rivers are to be made available to the Rajasthan Canal to irrigate mainly the desertic tract covering parts of western Rajasthan in India.