📑 Topics on this page (Jump to Topic):
📌 1. Monsoon Mechanism
- "Monsoon" comes from the Arabic "mausim" — seasonal reversal of winds. India has a tropical monsoon climate.
- Factors: differential heating of land and sea, northward shift of the ITCZ (to the Ganga plain) in summer, heating of the Tibetan Plateau, the subtropical westerly jet moving north of the Himalayas and the onset of the tropical easterly jet, high pressure near Madagascar.
- The SW monsoon reaches the Kerala coast around 1 June; covers India by ≈ 15 July. Two branches — the Arabian Sea branch (stronger) and the Bay of Bengal branch.
- Burst of monsoon — sudden onset of heavy rain; break in monsoon — dry spells during the rainy season.
- Retreating monsoon (Oct-Nov) — "October heat"; picks up moisture over the Bay of Bengal and rains on Tamil Nadu — the NE monsoon. Hence Tamil Nadu (Coromandel) gets most rain in winter.
📌 2. Seasons of India (IMD)
| Season | Months | Features |
|---|---|---|
| Cold weather | Dec-Feb | Western disturbances (from the Mediterranean) — winter rain in Punjab-Haryana, good for rabi (wheat) |
| Hot weather | Mar-May | Loo (north); mango showers (Kerala-Karnataka); Kalbaisakhi (WB); blossom/coffee showers (Karnataka); Bardoli Chheerha (Assam) |
| SW monsoon | Jun-Sep | ≈ 75% of annual rain |
| Retreating monsoon | Oct-Nov | October heat; cyclones on the east coast |
📌 3. Rainfall Distribution
- Highest rainfall: Mawsynram (≈ 11,870 mm) and Cherrapunji/Sohra — Khasi hills, Meghalaya; the funnel-shaped Garo-Khasi hills trap the Bay branch.
- Lowest: western Rajasthan (Jaisalmer), Ladakh (Leh — cold desert).
- The windward slope of the Western Ghats (Malabar, Konkan) gets heavy rain; the leeward interior Deccan lies in the rain shadow.
- The Arabian Sea branch runs parallel to the Aravallis, so Rajasthan gets little rain.
📌 4. El Niño, La Niña & IOD
- El Niño ("Christ child") — abnormal warming of the eastern Pacific (Peru coast); linked to a weak monsoon/drought in India.
- La Niña — cooling of the eastern Pacific; usually a good monsoon in India. ENSO = El Niño Southern Oscillation.
- Indian Ocean Dipole (IOD) — a positive IOD (warmer western Indian Ocean) helps the Indian monsoon.
- India Meteorological Department (IMD) — est. 1875, HQ New Delhi; Köppen types in India include Aw, Am, Cwg, BWhw.
⚠️ Exam Traps:
- Most rain on the Tamil Nadu coast comes from the NE (retreating) monsoon in Oct-Dec.
- Western disturbances come from the Mediterranean, not the Bay of Bengal.
- Kalbaisakhi = WB; mango showers = Kerala/Karnataka; Loo = North India.
- El Niño → usually less rain in India; La Niña → more.
📌 5. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. Where does the SW monsoon first reach India? Practice
Correct answer: (B)
Usually around 1 June on the Kerala coast.
Usually around 1 June on the Kerala coast.
Q2. Most of India's annual rainfall comes from the — Practice
Correct answer: (C)
≈ 75% of rain falls in June-September.
≈ 75% of rain falls in June-September.
Q3. Which place in India receives the highest rainfall? Practice
Correct answer: (D)
Mawsynram (Meghalaya) averages ≈ 11,870 mm.
Mawsynram (Meghalaya) averages ≈ 11,870 mm.
Q4. Tamil Nadu receives most of its rain in — Practice
Correct answer: (A)
The retreating/NE monsoon brings moisture from the Bay of Bengal.
The retreating/NE monsoon brings moisture from the Bay of Bengal.
Q5. Winter rain in NW India is caused by — Practice
Correct answer: (B)
Cyclonic disturbances from the Mediterranean help rabi crops.
Cyclonic disturbances from the Mediterranean help rabi crops.
Q6. "Kalbaisakhi" is associated with — Practice
Correct answer: (C)
Evening thunderstorms in WB-Assam in summer; useful for tea, jute, rice.
Evening thunderstorms in WB-Assam in summer; useful for tea, jute, rice.
Q7. "Mango showers" occur in — Practice
Correct answer: (D)
Pre-monsoon showers help mangoes ripen early.
Pre-monsoon showers help mangoes ripen early.
Q8. "Loo" is a — Practice
Correct answer: (A)
Hot dry wind of the northern plains in May-June.
Hot dry wind of the northern plains in May-June.
Q9. "October heat" is associated with the — Practice
Correct answer: (B)
Clear skies and high humidity during the retreat cause sultry heat.
Clear skies and high humidity during the retreat cause sultry heat.
Q10. El Niño usually has what effect on the Indian monsoon? Practice
Correct answer: (C)
Warming of the eastern Pacific often brings deficient rain to India.
Warming of the eastern Pacific often brings deficient rain to India.
Q11. The word "monsoon" is derived from — Practice
Correct answer: (D)
Arabic "mausim" = season.
Arabic "mausim" = season.
Q12. A major reason for low rainfall in Rajasthan is that — Practice
Correct answer: (A)
Winds are not forced up by the range, so they do not rain.
Winds are not forced up by the range, so they do not rain.
Q13. Why does the interior Deccan east of the Western Ghats get little rain? Practice
Correct answer: (B)
Moisture is shed on the windward slope.
Moisture is shed on the windward slope.
Q14. When was the India Meteorological Department established? Practice
Correct answer: (C)
IMD was set up in 1875; HQ New Delhi.
IMD was set up in 1875; HQ New Delhi.
Q15. In summer the ITCZ shifts to — Practice
Correct answer: (D)
Its northward shift forms the monsoon trough.
Its northward shift forms the monsoon trough.
Q16. Which is considered favourable for the Indian monsoon? Practice
Correct answer: (A)
A warmer western Indian Ocean (positive IOD) strengthens the monsoon.
A warmer western Indian Ocean (positive IOD) strengthens the monsoon.
Q17. Dry spells during the monsoon are called — Practice
Correct answer: (B)
In a "break" there is little rain for days or weeks.
In a "break" there is little rain for days or weeks.
Q18. Why does Ladakh (Leh) get very little rain? Practice
Correct answer: (C)
Monsoon winds cannot cross the Great Himalaya.
Monsoon winds cannot cross the Great Himalaya.
Q19. Summer thunderstorms in Assam are locally called — Practice
Correct answer: (D)
In Assam Kalbaisakhi is called "Bardoli Chheerha".
In Assam Kalbaisakhi is called "Bardoli Chheerha".
Q20. Pre-monsoon showers useful for coffee flowering in Karnataka are — Practice
Correct answer: (A)
In Karnataka they are "blossom showers".
In Karnataka they are "blossom showers".