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 is a line joining places that receive equal rainfall, so the 25 cm isohyet is a rainfall boundary, not a terrain or administrative boundary. Areas west of this line receive less than 25 cm of annual rainfall and form the arid western region associated with the Thar Desert. RajRAS / Connect Civils defines an isohyet and states that the 25 cm isohyet divides the desert into arid and semi-arid parts. Therefore, the line is best understood as separating Rajasthan's arid western belt from the comparatively semi-arid eastern side.
Why the other options are wrong
- (A) Desert is relevant to the arid side, but the 25 cm isohyet is a rainfall boundary and does not divide Rajasthan into desert and hilly regions.
- (B) Plains and plateau regions describe terrain, while an isohyet connects places of equal rainfall and marks a climatic division.
- (D) Northern and southern Rajasthan would imply a broad latitudinal split, whereas this rainfall line separates the arid west from the semi-arid east.
Concept
This tests Rajasthan climate mapping, especially how rainfall lines are used to classify arid and semi-arid regions. It recurs in RAS because rainfall distribution explains desert extent, water stress and regional geography.