RAS question
The Thar Desert in western Rajasthan receives an average annual rainfall of approximately:
Correct answer: (A) Less than 25 cm.
The core Thar Desert in western Rajasthan receives less than 25 cm of average annual rainfall.
Explanation
The question concerns the core desert belt, not Rajasthan's wider dry and semi-arid zone. Jaisalmer, Barmer, western Jodhpur and Bikaner lie in this belt, where annual rainfall is less than 25 cm, or 250 mm. Based on rainfall, the Thar Desert is divided into the arid or Rathi Region, with 0–25 cm of rainfall, and the semi-arid or Bangar Region, with 25–50 cm. The 25 cm isohyet separates these two parts. Therefore, less than 25 cm is the correct answer for the core western desert.
Why the other options are wrong
- (B) The 25–50 cm range belongs to the semi-arid Bangar transition belt, while the core arid Thar or Rathi belt lies below the 25 cm isohyet.
- (C) The 50–100 cm range corresponds to sub-humid eastern Rajasthan, not the low-rainfall core of the western Thar Desert.
- (D) More than 100 cm is associated with wetter south-eastern Rajasthan, including Banswara and Dungarpur, not the arid western Thar Desert.
Concept
This tests Rajasthan physical geography, especially rainfall isohyets and the arid–semi-arid division of the Thar Desert. It recurs in RAS because rainfall thresholds explain regional classification and variations in agriculture, vegetation and desert landscapes across western Rajasthan.