Climate — India
"The monsoon is India's true finance minister." — A saying that captures how much the rains matter.
1. Chapter Overview
India has a TROPICAL MONSOON climate. This chapter explains: the FACTORS controlling India's climate, the MECHANISM of the monsoon (why it comes in June and leaves in September), the FOUR SEASONS, and the distribution of RAINFALL across the country.
2. Factors Controlling India's Climate
1. Latitude
- Tropic of Cancer (23°30'N) passes through the MIDDLE of India
- Southern India = tropical (warm year-round). Northern India = subtropical (distinct winter).
2. The Himalayas
- Act as a CLIMATIC BARRIER: block COLD Central Asian winds (keeping N India warmer than same latitude in China)
- Force monsoon winds to RISE → orographic rainfall
3. Altitude
- Mountains (Himalayas, Western Ghats) are COLDER than plains
- Temperature decreases ~6.5°C per 1,000 m
4. Distance from the Sea (Continentality)
- Coastal areas: MODERATE temperatures (Mumbai: warm, but not extreme)
- Interior: EXTREME temperatures (Delhi: 45°C in summer, 5°C in winter)
5. Pressure and Winds
- The seasonal REVERSAL of winds is the ESSENCE of the monsoon
- January: high pressure over Central Asia → cold, dry winds from NE over India
- July: INTENSE LOW over NW India → draws moist SW winds from the ocean
6. Upper Air Circulation — Jet Streams
- Sub-tropical westerly jet: brings Western Disturbances (winter rain in NW India)
- Tropical easterly jet: develops in summer — steers monsoon depressions
7. Western Disturbances
- Cyclonic systems from the Mediterranean
- Bring WINTER RAIN (December–February) to NW India — vital for RABI crops (wheat)
3. The Monsoon Mechanism
What is the Monsoon?
- A SEASONAL REVERSAL of wind direction
- SW Monsoon (June–September): winds from ocean → land. WET.
- NE Monsoon (October–December): winds from land → ocean. DRY (except TN coast, where NE winds pick up moisture from Bay of Bengal → RAIN).
Why Does the Monsoon Occur?
- Differential heating: Land (India) heats up MUCH FASTER than the surrounding ocean in summer → INTENSE LOW PRESSURE forms over NW India
- Shift of ITCZ: The Inter-Tropical Convergence Zone shifts NORTH over India in summer → draws moist maritime air
- The Himalayas: Block the monsoon winds from escaping north → force them to RISE → orographic rain
- Jet stream: Tropical easterly jet steers monsoon depressions
Monsoon Burst and Break
- Burst: SUDDEN onset of heavy rain (Kerala coast ~June 1)
- Break: period of LITTLE OR NO rain during the monsoon season (days to weeks)
- Breaks are related to the movement of the MONSOON TROUGH
4. The Four Seasons
| Season | Months | Characteristics |
|---|---|---|
| Cold Weather (Winter) | Dec–Feb | Cool, dry. Pleasant in N India; warm in S India. Western Disturbances bring rain to NW. |
| Hot Weather (Summer) | Mar–May | INTENSE HEAT (45°C+ in NW). 'Loo' (hot, dry winds in N India). Pre-monsoon showers ('mango showers' in Kerala, 'Kal Baisakhi' in W Bengal). |
| Southwest Monsoon | Jun–Sep | ~75% of India's annual rainfall. Two branches: Arabian Sea (Western Ghats orographic rain) + Bay of Bengal. |
| Retreating Monsoon (Post-Monsoon) | Oct–Nov | Dry in most of India. Heavy rain on Tamil Nadu coast (NE Monsoon). Cyclones in Bay of Bengal. |
5. Distribution of Rainfall
High Rainfall Areas (>200 cm)
- Western Ghats (windward side)
- NE India (Meghalaya — Mawsynram: world's HIGHEST average annual rainfall)
- Andaman & Nicobar Islands
Moderate Rainfall (100–200 cm)
- Ganga Plains, central India, West Bengal, coastal Odisha and AP
Low Rainfall (50–100 cm)
- Interior Deccan (rain shadow of Western Ghats), W Rajasthan, parts of Gujarat, Haryana, Punjab
Very Low Rainfall (<50 cm)
- Thar Desert (western Rajasthan) — <15 cm
- Ladakh — cold desert, ~10 cm
6. Climatic Regions of India (Köppen)
- Amw (Monsoon with short dry season): W coast, NE India
- Aw (Tropical Savanna): most of Peninsular India
- BShw (Semi-arid): Rajasthan, Gujarat, interior Karnataka
- BWhw (Hot Desert): W Rajasthan
- Cwg (Humid Subtropical): Ganga plains, NE India
- Dfc (Cold, humid): parts of Himalayas
7. Exam Focus
- Factors controlling India's climate (7 factors)
- Monsoon mechanism — differential heating, ITCZ shift, Himalayan barrier, jet stream
- Four seasons with characteristics
- Monsoon burst and break
- Highest and lowest rainfall areas — Mawsynram and Thar/Ladakh
- Western Disturbances and their agricultural importance (rabi crops)
8. Conclusion
India's climate is the story of the MONSOON:
- FACTORS: Latitude, the Himalayas (barrier), altitude, continentality, pressure/wind reversal, jet streams, western disturbances
- MECHANISM: Land heats → intense low → ITCZ shifts north → moist ocean air sucked in → Himalayas force it up → RAIN
- SEASONS: Winter (cool, dry) → Summer (hot, dust storms, mango showers) → SW Monsoon (75% of rain) → Retreating (TN rain, cyclones)
- RAINFALL: Varies from Mawsynram's 1,141 cm to Ladakh's 10 cm
When the monsoon is late, a billion people watch the sky. When it arrives, a billion people breathe.
