Like its varying topography, Rajasthan has varying climate. The weather or climate of the Rajasthan can be broadly classified into four distinct seasons. They are - Pre-monsoon, which is the hot season preceding the monsoon and extends from April to June, the Monsoon that occurs in the month of June in the eastern region and mid- July in the western arid regions, the Post-monsoon that commences from mid-September and continues till November and the Winter that extends from December to March, January being the coldest month of the year. The average temperature in winter ranges from 8° to 28° C (46° to 82° F) and in summer the average temperature range from 25° to 46° C (77° to 115° F).
Rajasthan has varying topographic features though a major part of the state is dominated by parched and dry region. The extensive topography includes rocky terrain, rolling sand dunes, wetlands, barren tracts or land filled with thorny scrubs, river-drained plains, plateaus, ravines and wooded regions. In a more broad way the topography of Rajasthan can be divided in the following regions- the Aravalli or Hilly regions, the Thar and other arid regions, the Plateaus including Vindhaya and the Malwa, Fertile plains including the Mewar, the Forest Regions and Waterbodies including Rivers and Salt Lakes.
The soil and vegetation of Rajasthan alters with its wide-ranging topography of the state and the availability of water. The varied kind of soils available in Rajasthan are mostly sandy, saline, alkaline and chalky (calcareous). Clay, loamy, black lava soil and nitrogenous soils are also found.
Owing the limited rainfall seasonal vegetation such as a few grass species, shrubs and dwarf trees can be found. However food crops are grown in the plains that are drained by the rivers and streamlets owing to the alluvial and clay soil deposits. The hilly tracts of the Aravali are characterized by the black, lava soils that sustain the growth of cotton and sugarcane.
The Thar Desert or the Great Indian Desert encompasses about 70% of total landmass of Rajasthan and hence it is identified as the "Desert State of India". The Rajasthan desert which forms a major portion of the Thar Desert is the biggest desert in India and encompasses the districts of Jaisalmer, Barmer, Bikaner and Jodhpur. In fact the Rajasthan Desert comprises the desert triangle of three cities - Jaisalmer, Bikaner and Jodhpur. The desert becomes very hot during the summer and it experiences extreme climate with an average annual rainfall less than 25 cm. Days are hot and the nights are cold.
Rajasthan is the abode of certain flora and fauna that are particularly endemic to arid regions and are specially adapted biologically to survive in the dry, waterless regions of the state. Owing to the varied topography one can find an assortment of flora and fauna and avifauna in Rajasthan. The tree species found are teak, bamboo, varied species of acacia and khejri. Some National Parks house numerous species of herbs and plants that have medicinal values.The fauna of Rajasthan consists of 23 species of lizards and 25 species of serpents including the Spiny Tail Lizards and the Russel's Vipers.Other wildlife species include Antelopes, Indian Gazelles or Chinkaras, endangered Great Indian Bustard, Black Bucks, the Nilgai or the bluebull, wild cats, silver foxes and so on. There are about 450 species of avifauna including various migratory birds.