Thar Desert
The Thar Desert (also known as the Great Indian Desert) is a desert mainly located in the state of Rajasthan in northwest India. It continues into Pakistan as the Cholistan Desert. It is a region of constantly shifting sand dunes, with sparse vegetation in some areas.
Thar Desert is spread over northwestern India and eastern Pakistan covering an area of about 4,46,000 square kilometres. The Thar desert is about 805 km (about 500 mi) long and about 485 km (about 300 mi) wide. It covers four states of India and two states of Pakistan. The Thar Desert is bounded on the northwest by the Sutlej River, on the east by the Aravalli Range, on the south by the salt marsh known as the Rann of Kutch, and on the west by the Indus Valley. NASA has prepared a satellite map of the Thar Desert. http://www.gesource.ac.uk/worldguide/html/image_626.html

Indian desert
Indian Desert is the eastern part of the Thar Desert. It is spread over four states in India, namely Punjab, Haryana, Rajasthan, and Gujarat covering an area of 2,08,110 square kilometres. The maximum area is covered in Rajasthan, about 3/5th of the total geographical area of the state. Of the total desert in India 61% falls in Rajasthan, 20% in Gujarat and 9% in Punjab and Haryana combined. The Indian Desert is said to be extending at a rate of ½ km per year towards Punjab, Haryana, Uttar Pradesh and Madhya Pradesh. Indian Desert is mainly inhabited by Hindus but Muslim population is also there in minority. The Thar Desert also extends to the southeast of Pakistan. Within south Pakistan it is inhabited by Sindhi and kolhis.

Origin of Thar Desert
The origin of the Thar Desert is a controversial subject. Some consider it to be 4000 to 10,000 years old, whereas others state that aridity started in this region much earlier. Another theory states that area turned to desert relatively recently: perhaps around 2000 - 1500 BCE. Around this time the Ghaggar ceased to be a major river and now terminates in the desert. It has been observed through remote sensing techniques that Late Quaternary climatic changes and neotectonics have played a significant role in modifying the drainage courses in this part and a large number of palaeochannels exist.
Most of the studies have the same opinion with the palaeochannels of the Sarasvati coinciding with the bed of present day Ghaggar and believe that the Satluj along with the Yamuna once flowed into the present Ghaggar riverbed. It is postulated that the Sutlej is the main tributary of the Ghaggar and that subsequently the tectonic movements might have forced the Satluj westwards, the Yamuna eastwards and the Ghaggar dried.

Remote sensing is widely useful for revealing the palaeochannels in the desert areas using various digital image processing techniques of satellite images. The present disorganized state of many streams in the Thar desert of Western Rajasthan has been attributed by many investigators to change in climate during Quaternary, and in the particular Holocene.

Climate of desert
The climate of the desert region is characterized by extremes of temperatures ranging from even below freezing point in winters to as high as 52 °C in summers. Rainfall is precarious and erratic, ranging from below 120 mm in the extreme west to 375 mm eastward. These rains are of the monsoon type (July to September) and are generally of thundershowers. Mean wind velocity varies from about 3 km per hour during December and January to about 32 km per hour during May and June. Dust storms are also a normal feature during summers. The velocity of dust storms may reach as high as 130 km per hour, and may deposit as much as about 50 mm to 75 mm of dust on the floor of residential buildings. Frosts are severe during winters in the sandy areas and tree saplings up to 2 m height some times succumb to such frosts.

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