The great Indian desert (Thar Desert)

This is an area in which the vegetation cover is par and the ground surface is the exposed to the atmosphere and the associated physical forces. Rainfall is scanty, infrequent and irregular. the desert is the Eastern section of the Sahara Arabian desert and is also known as Thar desert (earlier it was known as Tharparkar desert; Tod Rajasthan). Thar desert extends over 1.3 million square kilometre; it is half of the Arabian desert and one seventh of the Sahara desert. 

Climate

The climate is characterized by extremes of temperature, severe draught accompanied by high wind velocity, low relative humidity, evaporation for more than rainfall and to scanty rainfall to support any appreciable vegetation.

The winters are quite cold, temperatures, sometimes below freezing point while heat during summer is intense and scorching. Hot season prevails from April to June, May being the hottest. The mean maximum temperature ranges from 39 degree Celsius to 42 degree Celsius during these months, whereas the mean minimum temperature ranges from 25 degree Celsius to 28 degree Celsius. December to January is cold weather, January being the coldest.

Rainfall is scanty and erratic with 10 cm  or more rains. Average rainfall for the last 10 years is 315.26 mm, 302.14 mm (Barmer). Most rainfall occurs during monsoon period of June to September. Winter rains are rare. Droughts occur quite frequently.

The wind from South-west to West is most common. Dust storms - Andhis  are quite frequent and in hot weather may be as strong as 136 kilometre per hour. In winter comma velocity is not hai. Rainfall is often associated with easterly winds.

                          Soil

Light texture and the loams form the bulk of soil. The layer of loose sediment is fairly deep. Clay is less in surface layers but may be up to 40% in the lowest layers. Salt impregnated patches occur throughout the area, particularlyc in Pachhadra in Barmer, Phalodi in Jodhpur and near Ramgarh in Jaisalmer district where halophytes abound. However consists of Sandy plains.

              Physical features

Pleistocene alluvial plains varying cover by younger wind worked sands constitutes by far the most extensive feature of the arid region. These plains have an elevation of 350 to 450 metre above the mean sea level.

Most spectacular among the landforms are the the dunes, which in arid Rajasthan cover, in varying degrees of frequency, 58% of the area. Dunes occur in two major chains- one lying in the western part of Barmer, Jaisalmer and Bikaner districts, made up of often 20-100 m high and many kilometres long dunes, and the other covering Eastern part of Bikaner and churu districts.discontinuous dune fields are scattered in the major part of the raised area. The dunes are of six types - obstacle, parabolic and coalesced parabolic, longitudinal, transverse, barchan and shrub coppice.