RAS question
The 25 cm isohyet line roughly divides Rajasthan into which two regions?
Correct answer: (C) Desert and Semi-arid.
The 25 cm isohyet roughly separates Rajasthan's desert region from its semi-arid region.
Explanation
The key is that the 25 cm isohyet is a rainfall boundary, not a political or relief boundary. MaargX defines an isohyet as a line joining places with equal rainfall, and places the arid or Rathi region in the 0-25 cm rainfall belt and the semi-arid or Bangar region in the 25-50 cm belt. The 25 cm line is therefore the demarcation between the two rainfall zones. Areas west of this line are treated as true desert, while the zone beyond it is semi-arid rather than fully desert. So the answer is the climatic division between desert and semi-arid Rajasthan.
Why the other options are wrong
- (A) North and South is a compass-direction split, while the 25 cm line is a rainfall demarcation between arid and semi-arid desert zones.
- (B) East and West describes a broad direction, but the tested division is named by climate: desert or arid on one side and semi-arid on the other.
- (D) Plains and Plateau is a relief-based classification, whereas the 25 cm isohyet is used here to separate rainfall-defined 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 explain desert distribution, vegetation, agriculture and settlement patterns in western Rajasthan.