RAS question
The main reason for scanty rainfall in western Rajasthan is:
Correct answer: (C) Aravalli Range lies parallel to the Arabian Sea monsoon branch.
Western Rajasthan receives scanty rainfall mainly because the Aravalli Range runs parallel to the Arabian Sea branch of the southwest monsoon, so it does not intercept the moisture-bearing winds.
Explanation
The key is the alignment of the Aravalli Range. The range runs roughly southwest to northeast, broadly parallel to the Arabian Sea monsoon winds. The Rajasthan State Biodiversity Board, Department of Environment, Government of Rajasthan notes that the Aravallis do not intercept the moisture-giving southwest monsoon winds from the Arabian Sea because the range lies parallel to their direction, leaving the northwestern region in a rain shadow. Since the winds are not forced to rise across a perpendicular mountain barrier, they pass over western Rajasthan without producing significant rain. That is why the correct cause is not merely desert location, but the monsoon-wind alignment with the Aravallis.
Why the other options are wrong
- (A) Proximity to the sea cannot explain scanty rainfall here because western Rajasthan is far from the sea, while the Aravallis fail to intercept Arabian Sea monsoon winds.
- (B) Dense forest cover is the opposite of the regional condition, as western Rajasthan has very sparse vegetation rather than forests that could shape rainfall.
- (D) High altitude is not the cause because western Rajasthan is a low-lying desert region.
Concept
This tests the physical geography link between relief, monsoon-wind direction and rain-shadow conditions in Rajasthan. It recurs in RAS because the Aravalli alignment is central to explaining the sharp rainfall contrast between western and eastern Rajasthan.