Which one of the following causes is responsible for rainfall during winters in north-western part of India ?
- (a)Retreating Monsoon
- (b)Cyclonic depression
- (c)Western disturbances
- (d)South-West Monsoon
Correct — C, Western disturbances. Winter rainfall over north-western India (Punjab, Haryana, western Uttar Pradesh, Himachal Pradesh, Jammu & Kashmir and northern Rajasthan) is caused by western disturbances — extratropical cyclonic storms that originate over the Mediterranean/Caspian region and travel eastward, embedded in the subtropical westerly jet stream. They bring light-to-moderate winter rain to the plains and snowfall to the western Himalayas, and are vital for the rabi crop, especially wheat.
- (a)Retreating Monsoon — Wrong — the retreating (north-east) monsoon brings October-December rain mainly to south-eastern India, notably the Tamil Nadu (Coromandel) coast, not winter rain to the north-west.
- (b)Cyclonic depression — Wrong — tropical cyclonic depressions form over the Bay of Bengal/Arabian Sea and affect the coasts in the monsoon and post-monsoon seasons; they are not the cause of NW-India winter rain.
- (d)South-West Monsoon — Wrong — the south-west monsoon is the June-September rainy season that delivers most of India's annual rainfall; it is a summer phenomenon, not a winter one.
Western disturbances are non-monsoonal, eastward-moving extratropical (temperate) cyclones that form over the Mediterranean/Caspian region and are steered across into north-west India by the mid-latitude westerlies and the subtropical westerly jet stream in winter. Over NW India between December and February they produce winter rain on the plains and snowfall in the western Himalayas.
The trap is distinguishing four rainfall mechanisms by season and region: the SW monsoon (summer, most of India), the retreating/NE monsoon (autumn, SE coast), tropical depressions (coasts), and western disturbances (winter, NW India). Only the last fits 'winter' and 'north-west'.
- Western disturbances originate over the Mediterranean/Caspian region and move eastward in the subtropical westerly jet.
- They bring winter (Dec-Feb) rain to NW India's plains and snow to the western Himalayas.
- This winter rain is crucial for rabi crops, especially wheat.
- By contrast, the retreating/NE monsoon brings winter rain to the Tamil Nadu (Coromandel) coast.
- Confusing western disturbances (winter, NW India) with the retreating monsoon (autumn, SE coast)
- Thinking western disturbances are tropical cyclones — they are extratropical (temperate) systems
The cause of winter rain in NW India, the origin/path of western disturbances, or their importance for rabi/wheat.
Consider the following statements: 1. The winds which blow between 30 degrees N and 60 degrees S latitudes throughout the year are known as westerlies. 2. The moist air masses that cause winter rains in North-Western region of India are part of westerlies.
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer(b) 2 only
Same concept — winter rains in NW India are the western disturbances, carried by the mid-latitude westerlies (statement 2 is the correct one).
- practice — not a real PYQ
Western disturbances that cause winter rain in north-western India originate over the:
- (a)Bay of Bengal
- (b)Mediterranean region
- (c)Indian Ocean
- (d)Arabian Peninsula
Answer(b) Mediterranean region — they travel east in the westerly jet to reach NW India.
- practice — not a real PYQ
Winter rainfall from western disturbances is most beneficial to which crop?
- (a)Rice (kharif)
- (b)Wheat (rabi)
- (c)Jute
- (d)Cotton
Answer(b) Wheat (rabi) — timely winter rain boosts the standing rabi wheat crop.