Climate of India and Tamil Nadu — TNPSC Group II/IIA Geography
Overview
India has a diverse climate influenced by the Himalayas, Indian Ocean, and the two monsoons. Tamil Nadu has a unique climate in that it receives its major rainfall from the Northeast monsoon, unlike most of India. For TNPSC Group 2/2A, focus on the two monsoons, their mechanisms, rainfall distribution, and cyclones affecting Tamil Nadu.
Factors Affecting India's Climate
| Factor | Effect |
|---|---|
| Latitude | Tropical to subtropical; temperatures vary north-south |
| Himalayas | Barrier against cold Central Asian winds; forces SW monsoon to rise and rain |
| Indian Ocean | Source of moisture for monsoons; moderates temperature of peninsula |
| Western Ghats | Force SW monsoon to rise; heavy rain on western slopes; rain shadow on east |
| Altitude | Temperature decreases 6.5°C per 1000m |
| Jet streams | Upper atmosphere winds influence monsoon timing |
The Four Seasons of India
1. Cold Weather Season (Winter) — December to February
| Feature | Details |
|---|---|
| Temperature | 10–15°C in north; 22–25°C in south |
| Wind | Northeast Trade Winds — from land to sea |
| Rainfall | Mostly dry; Western disturbances bring rain to Punjab/Himachal |
| Special | Tamil Nadu — NE monsoon rainfall continues in early December |
Western Disturbances:
- Low-pressure systems from Mediterranean region
- Bring rainfall to Punjab, Haryana, western UP, Jammu (November–March)
- Cause snowfall in Himachal Pradesh, Kashmir, Uttarakhand
- Important for Rabi crop (wheat)
2. Hot Weather Season (Summer) — March to May
| Feature | Details |
|---|---|
| Temperature | 35–45°C in north India; 40–48°C in Rajasthan |
| "Loo" | Hot, dry, dusty westerly winds in north India (May–June) |
| Dust storms | Common in Rajasthan and north India |
| Pre-monsoon | "Mango showers" in Karnataka/Tamil Nadu; "Nor'westers/Kalbaishakhi" in West Bengal/Bangladesh |
| Tamil Nadu | "Kattai Kaatru" (hot wind); temperatures 38–42°C |
Mango Showers (Coromandel Showers):
- Pre-monsoon rainfall in Tamil Nadu (April–May)
- Local convectional rainfall
- Helps mango crop ripening
3. Advancing Southwest Monsoon (June to September)
| Feature | Details |
|---|---|
| Entry | Enters Kerala around June 1 |
| Branches | Arabian Sea Branch + Bay of Bengal Branch |
| Coverage | Covers entire India by July 15 |
| Rainfall | 75–80% of India's annual rainfall |
| Wind direction | Southwest (from sea to land) |
Arabian Sea Branch:
- Hits Western Ghats first; heavy rain on western slopes (Cherrapunji area indirectly)
- One branch goes to Punjab via Rajasthan (east side of Western Ghats is dry)
- Kerala, Karnataka, Maharashtra, Gujarat — heavy rainfall
Bay of Bengal Branch:
- Hits Orissa, Bengal, then turns west
- Reaches Bihar, UP, Rajasthan
- Cherrapunji (Sohra), Meghalaya: Receives India's (and world's) highest rainfall — 11,872mm annually
- Mawsynram receives even more (12,000mm+)
Tamil Nadu's Situation During SW Monsoon
- Western Ghats block SW monsoon's moisture from reaching Tamil Nadu's interior
- Rain shadow zone: Coimbatore, Madurai, Tirunelveli receive less rainfall from SW monsoon
- Only coastal areas and the Nilgiris get SW monsoon rain
- Tamil Nadu relies mainly on Northeast monsoon for annual rainfall
4. Retreating Monsoon / Northeast Monsoon — October to December
| Feature | Details |
|---|---|
| Process | SW monsoon retreats from NW India (October) southward |
| Bay of Bengal crossing | Picks up moisture from Bay of Bengal |
| Wind direction | Northeast (from land to sea — but with Bay moisture) |
| Regions affected | Tamil Nadu, Southeast Andhra Pradesh, parts of Karnataka, Sri Lanka |
| Tamil Nadu rainfall | 48–60% of annual rainfall from NE monsoon |
Tamil Nadu's NE Monsoon (Kudirai Kai Mazhai):
- October, November, December — main rainy season in Tamil Nadu
- Chennai: Average annual rainfall = 1400mm; 60% in Oct–Dec
- Cyclone season: NE monsoon coincides with cyclone season in Bay of Bengal
- Important rivers: Cauvery, Vaigai, Tamirabarani, Palar — fed by NE monsoon
Rainfall Distribution in India
| Region | Annual Rainfall | Main Source |
|---|---|---|
| Western Ghats (western slopes) | 250–500 cm | SW monsoon |
| Northeast India | 200–400 cm | Bay of Bengal branch |
| Rajasthan/Thar Desert | < 20 cm | Rain shadow; far from moisture |
| Deccan Plateau (interior) | 50–100 cm | SW + NE monsoon |
| Tamil Nadu | 60–100 cm | Mainly NE monsoon |
| Nilgiris | 300–400 cm | Both SW and NE monsoon |
Cyclones
Formation
- Warm ocean (>26°C) heats air → air rises → low pressure → surrounding air spirals in
- Bay of Bengal is warmer → more cyclones than Arabian Sea
Cyclone Seasons in India
| Season | Type | Region |
|---|---|---|
| Pre-monsoon (April–May) | Rare | Bay of Bengal, Arabian Sea |
| Post-monsoon (Oct–Dec) | Most frequent | Bay of Bengal → Tamil Nadu, AP, Odisha |
Famous Cyclones Hitting Tamil Nadu
| Cyclone | Year | Impact |
|---|---|---|
| Bhola Cyclone | 1970 | Bangladesh/India; deadliest cyclone |
| 1977 Andhra Cyclone | 1977 | Andhra/Tamil Nadu border |
| 1984 Tamil Nadu Cyclone | 1984 | Severe damage in north TN |
| Nisha | 2008 | Tamil Nadu; severe flooding |
| Thane | 2011 | Hit Cuddalore; 56 deaths |
| Vardah | 2016 | Hit Chennai; uprooted trees |
| Gaja | 2018 | Hit Nagapatnam; 63 deaths |
| Nivar | 2020 | Hit Puducherry/north TN |
| Mandous | 2022 | Hit Mahabalipuram area; Chennai flooding |
Cyclone Warning System
- India Meteorological Department (IMD): Issues cyclone warnings
- Alert categories: Pre-Cyclone Watch (> 72 hrs), Cyclone Alert (48–72 hrs), Cyclone Warning (24–48 hrs), Post-Landfall Outlook
- NDRF (National Disaster Response Force): Deployed for rescue
- Early Warning System: Satellite, radar (Doppler Weather Radar in Chennai)
India Meteorological Department (IMD)
| Aspect | Details |
|---|---|
| Established | 1875 |
| Headquarters | New Delhi |
| Functions | Weather forecasting, cyclone warnings, monsoon forecast |
| Director General | Dr. Mrutyunjay Mohapatra (current) |
| Regional offices | Mumbai, Kolkata, Nagpur, Chennai, New Delhi |
Key Facts for TNPSC Group II/IIA
- SW Monsoon: Enters Kerala around June 1; covers India by July 15; gives 75% of India's rainfall
- NE Monsoon: October–December; Tamil Nadu receives 48–60% of annual rainfall from it
- Cherrapunji/Mawsynram (Meghalaya): Highest rainfall in India — Bay of Bengal branch + orographic effect
- Thar Desert (Rajasthan): Lowest rainfall — < 20cm; rain shadow area
- Tamil Nadu's rain shadow: Western Ghats block SW monsoon; interior TN is semi-arid
- Cyclone season: October–December in Bay of Bengal; affects Tamil Nadu coast
- Loo: Hot dry wind in north India (May–June); up to 45°C
- Western Disturbances: Mediterranean system; bring winter rain to Punjab/UP; important for wheat
- Doddabetta (Nilgiris) receives rainfall from BOTH SW and NE monsoons
- IMD established 1875: Issues monsoon and cyclone forecasts
Previous Year MCQ Patterns
Q: Tamil Nadu receives most of its annual rainfall from: a) Southwest Monsoon b) Northeast Monsoon c) Western Disturbances d) Convectional Rainfall
Q: Which place receives the highest rainfall in India? a) Cherrapunji (Sohra), Meghalaya b) Mawsynram, Meghalaya c) Agumbe, Karnataka d) Amboli, Maharashtra
Q: The Southwest Monsoon enters India first through: a) Gujarat coast b) Goa c) Kerala coast d) Tamil Nadu coast
Frequently Asked Questions
India receives rainfall from two monsoons: (1) Southwest (SW) Monsoon (June–September): Blows from Arabian Sea and Bay of Bengal; brings ~75% of India's annual rainfall; enters India from Kerala around June 1. (2) Northeast (NE) Monsoon (October–December): Retreating SW monsoon picks up moisture from Bay of Bengal and brings rainfall to Tamil Nadu and southeastern India. Tamil Nadu receives 48–60% of its annual rainfall from the NE monsoon.