The Climate of Rajasthan in northwestern India is generally arid or semi-arid and features fairly hot temperatures over the year with extreme temperatures in both summer and winter. Some of important Climatic perameters in state which are responsible for overall change in climate are :

Atmospheric Sea Level Pressure and Winds:

There is a very systematic manner in which the seasonal variations of atmospheric pressure take place over the state, with a maximum in the winter (January) and a minimum in the monsoon season (July). Except during the late summer and monsoon season the pressure gradient generally remains weak over the state. During winters the higher pressure is to the north and during summers the pressure decreases from south to north in Rajasthan. The light winds are mainly from northwest-north-northeast over the state in January which gradually turn anti-clockwise replaced by light north-westerly to westerly or south-westerly winds in April. In July with the advance of the summers, the pressure gradient increases and correspondingly the winds from northwest to southwest also strengthen reaching their maximum strength. The pressure decreases from west-southwest to eastnortheast over the state, in July. Having the weakest pressure gradient the month of October is the transition period. The changeover of the pressure and wind pattern commences and north-northeasterly winds appear October onwards.

Cloudiness :

 It is cloudless or slightly clouded during October to May but the part of the period from January to March is more clouded, especially during afternoons. The sky remains cloudless or lightly clouded over the state during April and May. During July and August, the monsoon skies are heavily clouded. The skies remains overcast for 5 days and clear on 7 days per month in West Rajasthan and for more than 8-9 days and clear on 4-5 days per month in East Rajasthan on an average during July and August. The cloud cover decreases to a great extent over the entire state during October.

Thunderstorms and Dust storms  :

For the occurrence of thunderstorms and dust storms convective activity is essential. Thunder activity becomes pronounced due to ground heating with the advance of the summer and when the moisture is insufficient in the atmosphere, dry thunderstorms or dust storms occur. Maximum numbers of thunderstorms occur, with the approach of the monsoon current, while dust storms are mainly confined to the summer months of March-June. Hail is sometimes accompanied with Pre-monsoon and monsoon thunderstorms. The maximum occurrences of thunderstorms are during July in the state and minimal in the months from November to January. The average number of days of during the monsoon season is about 11 in West Rajasthan and 10 in East Rajasthan. The average annual number of thunderstorms in the West and East Rajasthan are 17.0 and 15.0.

Fog :

 Fog occurs occasionally due to lack of sufficient moisture in the region. The maximum frequency of occurrence of fog is during December and January in both Western and Eastern Rajasthan. The favorable Conditions for occurrence of radiation fog like light to calm winds, clear skies etc. exist after the withdrawal of the monsoon till the month of February. During the monsoon season hill fog occurs at few places, when air is almost saturated and is easily cooled below the dew point while rising over high elevations.

Rainfall distribution :

 During the south-west monsoon period extending from June to September the state receives about 90% of the total rainfall. The cold weather period (January and February) receive the Remaining portion of rainfall which occurs in association with the local convective activity. There is a wide variation in the mean annual rainfall over Rajasthan as the extreme western parts of Jaisalmer district receive rainfall less than 100mm in contrast to more than 900mm in the eastern parts of Jhalawar and Banswara.

 The lowest recorded annual rainfall in the past 100 years i.e. between 1900 and 2010 was 24 mm in the western Rajasthan and whereas it was never below 120 mm in the eastern Rajasthan.

Air temperature and relative humidity conditions :

 The pleasant winters in the state witness mean night temperatures above 4.7oC to 10.6oC. During summers the western Rajasthan becomes the hottest place in the country with mean maximum air temperatures varying from 38.6oC to 42.6oC in May. The recorded extreme temperatures in the state were -4.4oC to 50.0oC in the western Rajasthan and -2.8oC to 47.8oC in the eastern Rajasthan (Indian Meteorological Department, 2010).

The relative humidity in the arid region of Western Rajasthan is also quite high because of the unfavorable circulations of the atmosphere and low precipitation that occurs in the arid region as compared to other semi-arid and sub-humid regions.

Wind regime and associated phenomena  :

The wind directions are mostly south-westerlies or west-south-westerlies during large part of the year whereas during winter they are northeast to north. During the winter season the Winds are light and variable but in summers especially around May to July strong winds prevail in the most parts of Rajasthan. Summers witness severe dust storm period too when the wind speed rises up to 60 kilometer per hour causing erosion from the dry soils.

Evapotranspiration  :

The annual potential evapotranspiration values vary widely between eastern and western Rajasthan. In Dungarpur and Banswara districts the annual potential evapotranspiration is less than 1300 mm whereas it is more than 2000 mm in Jaisalmer district.