RAS question
The 25 cm isohyet line roughly divides Rajasthan into which two regions?
Correct answer: (C) Desert and Semi-arid.
In Rajasthan's Thar Desert, the 25 cm isohyet roughly separates the arid desert region from the semi-arid region.
Explanation
The 25 cm isohyet is a rainfall boundary. An isohyet joins places receiving equal rainfall. On this basis, Rajasthan's Thar Desert is divided into the arid or Rathi region, which receives 0–25 cm of rainfall, and the semi-arid or Bangar region, which receives 25–50 cm. The 25 cm line therefore separates these two rainfall zones. The area west of it is arid desert, while the area receiving more rainfall is semi-arid. This is a climatic boundary, not a division based on direction or relief.
Why the other options are wrong
- (A) North and South is a compass-direction split, whereas the 25 cm isohyet marks a rainfall boundary between the arid and semi-arid regions.
- (B) East and West describes a broad direction, whereas the tested division is climatic: the arid desert region on one side and the semi-arid region on the other.
- (D) Plains and Plateau is a relief-based classification, whereas the 25 cm isohyet separates the rainfall-defined arid desert and semi-arid regions.
Concept
This tests Rajasthan climatology, especially the use of isohyets to classify arid and semi-arid zones. It recurs in RAS because rainfall boundaries help explain desert distribution, vegetation, agriculture and settlement patterns in western Rajasthan.