RAS question
The 25 cm isohyet (rainfall line) approximately divides Rajasthan into:
Correct answer: (C) Arid western Rajasthan and semi-arid eastern Rajasthan.
The 25 cm isohyet approximately divides Rajasthan into arid western Rajasthan and semi-arid eastern Rajasthan.
Explanation
An isohyet joins places that receive equal rainfall. The 25 cm isohyet is therefore a climatic boundary rather than a terrain, administrative or north-south boundary. West of it, annual rainfall is below 25 cm, forming the arid western region associated with the Thar Desert; to the east lies the comparatively semi-arid region. The line is also understood as dividing the desert into arid and semi-arid parts. Thus, in Rajasthan, it broadly separates the arid west from the semi-arid east.
Why the other options are wrong
- (A) The desert is associated with the arid western side, but the 25 cm isohyet is a rainfall boundary; it does not divide Rajasthan into desert and hilly regions.
- (B) Plains and plateaus are landform regions, whereas an isohyet joins places of equal rainfall and marks a climatic division.
- (D) A north-south division of Rajasthan would be a broad latitudinal split, whereas this rainfall line separates the arid west from the semi-arid east.
Concept
This question tests how rainfall lines are used to map Rajasthan's climate and distinguish arid from semi-arid regions. The concept matters for RAS because rainfall distribution helps explain the extent of the Thar Desert, regional water stress and Rajasthan's broader geography.