Factors Controlling Rajasthan's Climate

Rajasthan's climate is classified as hot semi-arid to arid over most of its area, with significant spatial variation driven by four primary controls.

2.1 Latitude and Continental Position

Rajasthan extends from 23°3'N to 30°12'N latitude — entirely within the tropical and sub-tropical zones. This latitude belt places it under the influence of the sub-tropical high pressure belt for much of the year, suppressing rainfall and causing high temperatures. The state's interior location, far from moderating oceanic influences, creates an extreme continental climate with high diurnal and annual temperature ranges.

• Diurnal temperature range in western Rajasthan: up to 25–30°C (desert climate characteristic)
• Annual temperature range in Jaisalmer: ~20°C (winter mean ~12°C, summer mean ~32°C)
• Jaisalmer is ~1,100 km from the Arabian Sea and ~1,300 km from the Bay of Bengal — among the most interior locations in peninsular India

2.2 The Aravalli Barrier

The Aravalli range runs NE–SW at an orientation that is parallel to, not perpendicular to, the Arabian Sea branch of the SW monsoon. This critical geometric fact explains why the Aravalli fails to intercept monsoonal moisture from the west:

• The Arabian Sea monsoon flows NE — parallel to the Aravalli orientation — and passes over the range without orographic uplift
• The Bay of Bengal branch (flowing NW) encounters the Aravalli at roughly right angles in southeastern Rajasthan, causing orographic rainfall in districts like Kota, Bundi, and Jhalawar (60–100 cm)
• Mt. Abu (Sirohi district, 1,722 m altitude) acts as an isolated interceptor of both branches, receiving ~150 cm — the state maximum
• Where the Aravalli is low or absent (northern districts: Bikaner, Ganganagar, Hanumangarh), the Thar Desert extends without climatic check

2.3 Distance from Sea and Monsoon Track

The SW monsoon follows two tracks into Rajasthan:

1. Arabian Sea Branch: Crosses Gujarat and Kutch before entering western Rajasthan. By the time it reaches Jodhpur-Barmer, it has deposited most moisture over Gujarat and the Aravalli piedmont. Result: <30 cm rainfall in Jodhpur, <10 cm in Jaisalmer.
2. Bay of Bengal Branch: Deflects NW after crossing central India (Vindhya-Satpura ranges). Enters Rajasthan from the southeast through Kota, Baran, and Jhalawar — the most rainfall-rich zone of the state (80–100 cm). Progressively weakens as it moves northwestward.

The North Arabian Sea branch (which bypasses Rajasthan through the sea) does not contribute directly. Post-monsoon (NE monsoon) has minimal impact on Rajasthan, unlike Tamil Nadu and Andhra Pradesh.

2.4 Relief and Altitude

Altitude modifies temperature significantly:

• Mt. Abu (1,722 m): Annual mean temperature ~20°C — a "hill station" anomaly in an otherwise hot state
• Aravallis (600–900 m): 3–5°C cooler than surrounding plains
• Fatehpur (Sikar district): Unusual case — low elevation (~300 m) but a cold winter pocket due to local topographic channeling of cold winds from the northwest; recorded minimum temperature of -8.8°C (January 1964, a historic low for Rajasthan)

---