CDS Geography · Indian Geography — Physical Features
Monsoon and Rainfall
Why one side of a mountain is wet and the other dry, how the two branches of the monsoon and the retreating monsoon share out the rain, and where India is coldest and driest.
Why this matters
Seven CDS questions from 2017 to 2021: 1 EASY, 5 MODERATE, 1 HARD. Each one turns on a single idea, the rain shadow or the path of a monsoon branch, so one clear picture answers them all.
Concept 1 of 3: Windward and leeward: the rain shadow
Wet monsoon wind rises when it meets a mountain, cools, and drops its rain on the side facing it (the windward side). By the time it crosses the top it is dry, so the far side (the leeward side) gets little rain. That dry far side is the rain shadow.
Definition
Examples in India:
- Western Ghats: the coast (Mumbai, Mangaluru) is windward and very wet; the plateau east of the Ghats (Pune, Bengaluru, interior Maharashtra) is leeward and much drier.
- Great Himalaya: Leh in Ladakh lies in its rain shadow and is a cold desert with about 100 mm of rain a year, less than Jodhpur in the Thar.
- Khasi hills: Mawsynram and Cherrapunji, on the windward slope, are the wettest places in India.
| Place | Side | Rain |
|---|---|---|
| Mumbai, Mangaluru | Windward of the Western Ghats | Very heavy |
| Pune, Bengaluru | Leeward of the Western Ghats | Low |
| Interior Maharashtra | Rain shadow of the Western Ghats | Low in the monsoonQ CDS 2017 (II): both statements true, and the rain shadow explains the low rain. |
| Leh | Rain shadow of the Great Himalaya | About 100 mm a year, the leastQ CDS 2020 (II): Leh gets less than Jodhpur, New Delhi or Bengaluru. |
| Mawsynram, Cherrapunji | Windward of the Khasi hills | The heaviest in India |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2018 · CDS (II) 2018 — General Knowledge · Q38Moderate
Example 1 · Indian Geography — Physical Features · Monsoon and Rainfall
Which one of the following places does not fall on leeward slope?
The coast is windward
Places on the west coast, such as Mangaluru, face the monsoon and are windward. The leeward, rain-shadow places are east of the Ghats, such as Pune and Bengaluru.
Leh, not the Thar, is the driest
The Thar is dry, but Leh in the rain shadow of the Himalaya gets even less: about 100 mm a year against roughly 350 mm at Jodhpur.
Concept 2 of 3: Monsoon branches and the retreating monsoon
The south-west monsoon splits around the peninsula into two branches. One crosses the Arabian Sea and hits the Western Ghats; the other crosses the Bay of Bengal, hits the north-east and turns west up the Ganga plain. In autumn the winds turn round, and the Tamil Nadu coast, dry all summer, gets its rain.
Definition
The pattern:
- The monsoon reaches Kerala around 1 June.
- Arabian Sea branch: the west coast and the Western Ghats, then on to central and north-west India.
- Bay of Bengal branch: Bengal and the north-east; the Himalaya turn it west along the Ganga plain.
- The two branches meet over north-west India, so Punjab and Haryana get rain from both.
- Retreating (north-east) monsoon, October to December: picks up moisture over the Bay of Bengal and gives the Coromandel coast of Tamil Nadu most of its yearly rain.
- Western disturbances: winter rain in Punjab and Haryana, good for the wheat crop.
| Wind | Who gets the rain |
|---|---|
| Arabian Sea branch | West coast, Western Ghats, then central and north-west India |
| Bay of Bengal branch | Bengal, the north-east, then west up the Ganga plain |
| Both branches together | North-west India, such as PunjabQ CDS 2021 (II): Punjab, not Maharashtra, Meghalaya or Tamil Nadu. |
| Retreating (north-east) monsoon | Coromandel coast of Tamil Nadu, October to December |
| Western disturbances | Punjab and Haryana in winter |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
CDS · 2018 · CDS (II) 2018 — General Knowledge · Q39Moderate
Example 2 · Indian Geography — Physical Features · Monsoon and Rainfall
South Arcot and Ramanathapuram receive over 50 percent of their annual rainfall from which one of the following?
Tamil Nadu's rain comes late
The Coromandel coast lies in the rain shadow during the south-west monsoon. It gets most of its rain from the retreating north-east monsoon, October to December.
Concept 3 of 3: Winter temperature and drought
In January the north of India is cold and the south stays warm, because the south is closer to the equator and surrounded by sea. Drought hits where rain is low and unreliable: the dry west, not the wet plains or the north-east.
Definition
Two facts:
- In January, the 20°C isotherm runs roughly along the Tropic of Cancer and splits India into a cooler north and a warmer south of about equal size.
- The most drought-prone areas are the dry west: Kachchh in Gujarat and western Rajasthan (west of the Aravalli). The Ganga plains, coastal Andhra Pradesh and the north-east get dependable rain.
| Fact | Answer |
|---|---|
| January isotherm that halves India | 20°C, near the Tropic of CancerQ |
| Most drought-prone regions | Kachchh and western Rajasthan |
| Regions with dependable rain | Ganga plains, coastal Andhra Pradesh, the north-east |
Practice this conceptself-check · 3 quick reps
The same idea in a real exam question:
CDS · 2021 · CDS (II) 2021 — General Knowledge · Q84Easy
Example 3 · Indian Geography — Physical Features · Monsoon and Rainfall
The Government wants to prepare a plan for drought prone areas of the country. Which one of the following regions will be predominantly focused ?
20°C, not 15°C or 25°C
The January isotherm that cuts India into two near-equal halves is 20°C, and it runs close to the Tropic of Cancer.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (3)
Windward and leeward: the rain shadow5 rows
| Place | Side | Rain |
|---|---|---|
| Mumbai, Mangaluru | Windward of the Western Ghats | Very heavy |
| Pune, Bengaluru | Leeward of the Western Ghats | Low |
| Interior Maharashtra | Rain shadow of the Western Ghats | Low in the monsoonQ CDS 2017 (II): both statements true, and the rain shadow explains the low rain. |
| Leh | Rain shadow of the Great Himalaya | About 100 mm a year, the leastQ CDS 2020 (II): Leh gets less than Jodhpur, New Delhi or Bengaluru. |
| Mawsynram, Cherrapunji | Windward of the Khasi hills | The heaviest in India |
Monsoon branches and the retreating monsoon5 rows
| Wind | Who gets the rain |
|---|---|
| Arabian Sea branch | West coast, Western Ghats, then central and north-west India |
| Bay of Bengal branch | Bengal, the north-east, then west up the Ganga plain |
| Both branches together | North-west India, such as PunjabQ CDS 2021 (II): Punjab, not Maharashtra, Meghalaya or Tamil Nadu. |
| Retreating (north-east) monsoon | Coromandel coast of Tamil Nadu, October to December |
| Western disturbances | Punjab and Haryana in winter |
Winter temperature and drought3 rows
| Fact | Answer |
|---|---|
| January isotherm that halves India | 20°C, near the Tropic of CancerQ |
| Most drought-prone regions | Kachchh and western Rajasthan |
| Regions with dependable rain | Ganga plains, coastal Andhra Pradesh, the north-east |
Watch out for (4)
- The coast is windward→ Windward and leeward: the rain shadow
- Leh, not the Thar, is the driest→ Windward and leeward: the rain shadow
- Tamil Nadu's rain comes late→ Monsoon branches and the retreating monsoon
- 20°C, not 15°C or 25°C→ Winter temperature and drought
Test yourself on Indian Geography — Physical Features
20 past CDS questions from this chapter, timed at 20 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.