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Geography

Key Points at a Glance

Climate of India: Monsoon, Rainfall Distribution, Climatic Regions

Paper II · Unit 3 Section 1 of 11 PYQ-style 28 min
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Key Points at a Glance

  1. India has a tropical monsoon climate with four distinct seasons: Winter (December-February), Pre-Monsoon/Hot-Dry Summer (March-May), SW Monsoon (June-September), and Retreating Monsoon/NE Monsoon (October-November).

  2. The SW Monsoon originates from the Inter-Tropical Convergence Zone (ITCZ) shifting northward over India in June; splits into Arabian Sea Branch (hits Western Ghats first; brings heavy rain to western India) and Bay of Bengal Branch (enters NE India/Bangladesh first; brings rain to Ganga plains).

  3. Mawsynram (Meghalaya) receives the world's highest annual rainfall - 11,871 mm (Cherrapunji/Sohra: 11,777 mm); both in the Khasi Hills funnel-shaped valley. Jaisalmer (Rajasthan) receives the lowest rainfall in India - ~150 mm per year.

  4. El Nino - warming of central/eastern equatorial Pacific (every 3-7 years) - weakens the Walker Circulation, suppresses SW monsoon, causing below-normal rainfall in India (drought risk). La Nina (cooling of Pacific) generally enhances SW monsoon, bringing excess rainfall.

  5. Western Disturbances (WDs) are mid-latitude cyclonic weather systems originating over the Mediterranean/Atlantic, travelling east along the subtropical jet stream to bring winter rainfall to NW India (Punjab, Haryana, Himachal, Uttarakhand, J&K). They cause 5-10 rainy days per month in winter months (December-February).

  6. The Tibetan Plateau acts as a thermal engine driving the monsoon - in summer, the plateau (avg 4,500 m) heats up rapidly, creating a powerful high-pressure heat source aloft; this heating enhances the upper-level anticyclone and intensifies the Arabian Sea branch of the monsoon.

  7. India's average annual rainfall is about 1,160.1 mm under the updated 1971-2020 normal - but distribution is highly uneven: the Northeast and west-facing Ghats receive >2,000 mm; the Thar Desert and rain-shadow Deccan receive <250 mm; and the Gangetic plains receive 600-1,200 mm.

  8. Monsoon onset and withdrawal: SW Monsoon typically arrives at Kerala (Thiruvananthapuram) on June 1 +/- 7 days; reaches Delhi by June 27-July 5; covers entire India by July 15; begins withdrawal from NW India in September; fully retreats by December 1 (replacing with NE monsoon).

  9. Northeast Monsoon (NE Monsoon) - October-December; reverse flow of winter winds from land (high pressure) to Bay of Bengal; brings rainfall to Tamil Nadu, southern AP, and Sri Lanka; Tamil Nadu receives its largest seasonal share of annual rainfall from the NE monsoon, with 48% in October-December and 36% in the SW monsoon season under IMD's 1971-2020 normals. Chennai receives most rain during October-December (NE monsoon), not SW monsoon.

  10. Koppen's climate classification for India: Tropical Monsoon (Am - most of India); Tropical Savanna (Aw - Deccan Peninsula); Semi-arid Steppe (BSh - interior Deccan, Rajasthan); Arid/Hot Desert (BWh - Thar Desert); Humid Subtropical (Cwa - Ganga Plain); Montane (H - Himalayas, high altitudes).

  11. Loo is a hot, dry, dusty wind that blows over the Indo-Gangetic Plain during April-June, bringing daytime temperatures to 45-50°C. It is strongest in Rajasthan, UP, and Bihar.

  12. India has 29 agro-climatic zones (as per ICAR) and 15 agro-climatic zones (as per Planning Commission); Trewartha's classification identifies 6 climate types; Stamp's classification identifies 4; RPSC typically uses Koppen (6 types) or general regional classification.