Climate
'India's CLIMATE is a MONSOON symphony — a grand, seasonal REVERSAL of winds that brings RAIN to a subcontinent and sustains over a BILLION lives.'
1. What is Climate?
Climate refers to the long-term average weather pattern of a region (over 30+ years). Weather refers to the short-term (daily/hourly) state of the atmosphere at a particular place and time.
| Aspect | Weather | Climate |
|---|---|---|
| Time scale | Hours to days | Decades to centuries |
| Variability | Highly variable, changes rapidly | Relatively stable, changes slowly |
| Example | 'Today is hot and humid in Visakhapatnam' | 'AP has a tropical monsoon climate with hot summers and moderate winters' |
2. Factors Affecting India's Climate
2.1 Latitude
India lies between 8°4′N and 37°6′N latitude. The Tropic of Cancer (23½°N) passes through the middle of India:
- Southern India (south of Tropic of Cancer): TROPICAL climate — near the Equator, temperatures remain relatively high throughout the year.
- Northern India (north of Tropic of Cancer): SUBTROPICAL climate — colder winters, greater temperature variation between summer and winter.
2.2 Altitude
Temperature DECREASES with altitude (~6.5°C per 1,000 m ascent). 'This is why Drass (Ladakh) at ~3,300 m is one of the coldest inhabited places in India (winter low: -40°C) even though it is at a relatively low latitude.'
2.3 Pressure and Winds
- India's climate is dominated by the monsoon wind system — the seasonal reversal of wind direction.
- Winter: High pressure over Central Asia (Siberian High) → cold, dry winds flow from the northwest toward the Indian Ocean.
- Summer: Low pressure over north India (due to intense heating) → moist winds flow from the Indian Ocean toward the land.
2.4 Distance from the Sea (Continentality)
- Coastal areas (e.g., Mumbai, Visakhapatnam, Chennai): Moderate climate — small temperature range due to maritime influence.
- Interior areas (e.g., Delhi, Hyderabad, Lucknow): Extreme climate — large temperature range (hot summers, cold winters) due to continental influence.
2.5 Ocean Currents and Relief
- Ocean currents: Warm and cold currents along India's coastline affect temperature and rainfall distribution.
- Relief: The Western Ghats act as a rain barrier — blocking the moisture-laden SW monsoon winds → very heavy rainfall on the western (windward) side, rain shadow (dry) on the eastern (leeward) side (including parts of AP Rayalaseema).
3. The Monsoon Mechanism
'The term MONSOON comes from the Arabic word "Mausim" meaning SEASON. It refers to the seasonal REVERSAL of wind direction.'
Key Factors Driving the Monsoon
| Factor | Explanation |
|---|---|
| Differential heating of land and sea | In summer, land heats up faster than the ocean → low pressure over the interior of India. Ocean remains cooler → high pressure over the Indian Ocean. Air flows from high (ocean) to low (land) — this is the SOUTHWEST MONSOON. |
| Inter-Tropical Convergence Zone (ITCZ) | The equatorial low-pressure belt where trade winds from both hemispheres converge. The ITCZ shifts northward during the northern summer, bringing rain to India. |
| Tropical Easterly Jet Stream | A high-speed wind current in the upper atmosphere. Its northward shift in summer is linked to the onset of the monsoon. |
| Subtropical Westerly Jet Stream | Flows south of the Himalayas in winter. In summer, it shifts north of the Tibetan Plateau — triggering the monsoon. |
| Tibetan Plateau heating | The Tibetan Plateau heats up in summer (average altitude ~4,500 m). This creates a thermal low in the upper atmosphere, strengthening the monsoon circulation. |
| Indian Ocean Dipole (IOD) and El Nino | IOD (temperature differences between the western and eastern Indian Ocean) and ENSO (El Nino Southern Oscillation) in the Pacific affect monsoon strength. El Nino (warming of Pacific) → WEAKER monsoon. La Nina (cooling of Pacific) → STRONGER monsoon. |
4. Seasons in India
India experiences FOUR major seasons:
4.1 Cold Weather Season (Winter) — December to February
| Feature | Detail |
|---|---|
| Temperature | Northern India: 10-20°C (day). Can drop to 0°C in north. Southern India: 20-30°C. |
| Winds | Northeast trade winds (cold, dry) flowing from Central Asia toward the Indian Ocean. |
| Rainfall | Very low across most of India. Some rainfall in Tamil Nadu and coastal AP from retreating monsoon (winter monsoon). |
| Key feature | Clear skies, low humidity, pleasant weather in most of India. |
4.2 Hot Weather Season (Summer) — March to May
| Feature | Detail |
|---|---|
| Temperature | 30-45°C across most of India. Highest recorded: ~51°C (Phalodi, Rajasthan, 2016). |
| Winds | Strong local winds: Loo (hot, dry, dusty winds from Rajasthan — dangerous, can cause heatstroke). |
| Rainfall | PRE-MONSOON showers: Mango showers (Kerala, Karnataka, AP — help mango ripening). Kal Baisakhi (West Bengal, Assam — violent thunderstorms). |
| Key feature | Lowest pressure in north India. The ITCZ shifts northward. |
4.3 Advancing Monsoon (Rainy Season / Southwest Monsoon) — June to September
| Feature | Detail |
|---|---|
| Onset | 1st June (Kerala) — gradually covers entire country by July 15. |
| Rainfall | 75-90% of India's ANNUAL rainfall falls in this season. |
| Two branches | Arabian Sea branch (brings rain to West Coast, Western Ghats) — blocked by Western Ghats. Bay of Bengal branch (brings rain to Northeast India, Eastern Coast, Ganga Plains). |
| Break in monsoon | Periods of no rain (drought-like conditions) between rainy spells — caused by the ITCZ shifting away. |
Monsoon onset over Kerala: The arrival of the SW monsoon over the Kerala coast on June 1 is a major national event — it marks the beginning of the agricultural season across India.
4.4 Retreating Monsoon (Post-Monsoon / Autumn) — October to November
| Feature | Detail |
|---|---|
| Process | The monsoon withdraws from north India. The ITCZ shifts southward. |
| Winds | Winds reverse direction — blow from land to sea (northeast direction). |
| Rainfall | Northeast Monsoon (winter monsoon): Tamil Nadu and coastal AP receive ~60% of their annual rainfall during THIS season — from the retreating monsoon winds crossing the Bay of Bengal. |
| Cyclones | October-November is the peak month for tropical cyclones in the Bay of Bengal — affecting AP, Odisha, Tamil Nadu, West Bengal coasts. |
5. Distribution of Rainfall
| Category | Annual Rainfall | Regions |
|---|---|---|
| Very high | 200+ cm | Western Ghats (windward side), Meghalaya (Mawsynram — world's wettest), Sub-Himalayan West Bengal. |
| High | 100-200 cm | Most of eastern India, Northeast India, Odisha coast. |
| Moderate | 50-100 cm | Central India, Deccan Plateau, most of AP (except Rayalaseema). |
| Low | 25-50 cm | Western Rajasthan, parts of Gujarat, Rayalaseema (AP). |
| Very low | <25 cm | Thar Desert (Jaisalmer, Bikaner — Rajasthan), Rann of Kutch. |
Mawsynram (Meghalaya) — the wettest place on Earth (~11,872 mm/year). Jaisalmer (Rajasthan) — one of the driest (~100 mm/year).
6. Andhra Pradesh — Climate
| AP Climate Feature | Detail |
|---|---|
| Climate type | Tropical Monsoon (Koppen classification: Aw — tropical wet and dry) |
| Summer | March to June. Hot and humid on the coast (Visakhapatnam: 32-37°C). Relatively less humid in Rayalaseema (Kurnool: 35-42°C). |
| Winter | December to February. Pleasant (coast: 20-30°C. Rayalaseema: 18-28°C). |
| Rainfall distribution | Coastal AP (Godavari, Krishna deltas): 900-1,100 mm/year. Rayalaseema: 500-700 mm/year (semi-arid). |
| Northeast Monsoon significance | Coastal AP (Nellore, Prakasam, Guntur, Krishna, East/West Godavari, Visakhapatnam) receives ~60% of its rainfall from the retreating monsoon (October-December) . Rayalaseema receives mainly from southwest monsoon (June-September). |
Why Rayalaseema is Drought-Prone
Rayalaseema (Kurnool, Anantapur, Kadapa, Chittoor districts) lies in the rain shadow of the Western Ghats. The SW monsoon winds deposit most of their moisture on the Western Ghats (windward side). By the time they cross the peninsula and reach Rayalaseema, they have lost most of their moisture → rainfall is low (500-700 mm/year) and highly variable. 'The agony of Rayalaseema is written in its geography — trapped between the Western Ghats' shadow and the variability of the northeast monsoon.'
Cyclone Vulnerability of AP Coast
AP has a 974 km coastline on the Bay of Bengal — making it one of the most cyclone-prone states in India. The October-December period is the peak cyclone season. Major cyclones: Hudhud (2014 — Visakhapatnam, devastating), Titli (2018 — Srikakulam), Nilam (2012), Laila (2010). AP has developed an advanced Cyclone Early Warning System and disaster preparedness infrastructure including multi-purpose cyclone shelters.
7. Common Mistakes
- 'Monsoon means heavy rainfall' — CORRECTION: Monsoon means seasonal reversal of winds — it can bring heavy rainfall (SW monsoon) or dry conditions (retreating monsoon).
- 'The SW monsoon brings rain to all parts of India equally' — CORRECTION: Rainfall distribution is highly uneven. The Western Ghats (west coast) receive very heavy rain, while the leeward side (east of Western Ghats, including Rayalaseema) receives much less.
- 'Tamil Nadu receives most of its rainfall from the SW monsoon' — CORRECTION: Tamil Nadu receives most of its rainfall from the Northeast (retreating) monsoon (October-December).
- 'India has only two seasons — summer and winter' — CORRECTION: India has FOUR seasons — Cold (Dec-Feb), Hot (Mar-May), Advancing Monsoon (Jun-Sep), Retreating Monsoon (Oct-Nov).
- 'El Nino always causes drought in India' — CORRECTION: El Nino TENDS to weaken the monsoon — but NOT always. Some El Nino years have had normal monsoon rainfall. La Nina generally strengthens the monsoon.
8. Exam Focus
| Topic | Marks (approx.) |
|---|---|
| Factors affecting India's climate | 3-4 |
| Monsoon mechanism (ITCZ, jet streams, differential heating) | 4-5 |
| Four seasons — characteristics | 4-5 |
| Distribution of rainfall | 2-3 |
| AP climate and cyclone vulnerability | 3-4 |
Key Facts for Quick Revision
- Climate ≠ Weather: Climate is long-term average; weather is short-term condition.
- SW Monsoon: June-September (75-90% of annual rainfall). NE Monsoon: October-December (Tamil Nadu, coastal AP).
- Wettest place: Mawsynram (Meghalaya) ~11,872 mm/year.
- Driest place: Jaisalmer (Rajasthan) ~100 mm/year.
- El Nino: Warmer Pacific → weaker Indian monsoon. La Nina: Cooler Pacific → stronger Indian monsoon.
- AP: Tropical monsoon. NE monsoon critical for coastal AP. Rayalaseema is drought-prone (rain shadow).
9. Quick Self-Test
- Distinguish between climate and weather. (Answer: Climate = long-term average (30+ years). Weather = short-term (daily/hourly) condition.)
- What is the monsoon and why does India experience it? (Answer: Seasonal reversal of winds caused by differential heating of land and sea, shifting of ITCZ, and jet streams.)
- Name the four seasons in India. (Answer: Cold (Dec-Feb), Hot (Mar-May), Advancing Monsoon (Jun-Sep), Retreating Monsoon (Oct-Nov).)
- Why does Tamil Nadu receive rainfall in winter? (Answer: From the Northeast (retreating) monsoon — winds cross the Bay of Bengal, pick up moisture, and bring rain to the Coromandel Coast.)
- What is the significance of the NE monsoon for Andhra Pradesh? (Answer: Coastal AP (Nellore to Visakhapatnam) receives ~60% of its annual rainfall from the retreating/NE monsoon — this is its MAIN rainy season.)
- Why is Rayalaseema drought-prone? (Answer: Lies in the rain shadow of the Western Ghats. The SW monsoon loses most moisture on the western side. Low and variable rainfall: 500-700 mm/year.)
- What are the two branches of the SW monsoon? (Answer: Arabian Sea branch (west coast) and Bay of Bengal branch (east coast/northeast).)
- Which place receives the highest and lowest rainfall in India? (Answer: Highest — Mawsynram (Meghalaya). Lowest — Jaisalmer (Rajasthan).)
- Name one major cyclone that hit AP and its impact. (Answer: Cyclone Hudhud (2014) — devastated Visakhapatnam, caused massive damage to infrastructure, trees, and power lines.)
- How does El Nino affect the Indian monsoon? (Answer: El Nino (warming of Pacific Ocean) tends to WEAKEN the monsoon, reducing rainfall in India.)
