Chapter Overview

India’s climate is tropical monsoon (उष्णकटिबंधीय मानसूनी): a seasonal reversal of winds brings about three-quarters of the year’s rain in just four months, June to September. The monsoon decides the kharif harvest, reservoir levels, food prices and even rural demand for goods. In Chhattisgarh, the “rice bowl”, a late onset or a long July break is felt in every village. This chapter explains how the monsoon works, how the seasons follow from it, where the rain falls and how reliably, and why distant oceans (El Niño, La Niña, the Indian Ocean Dipole) make some years good and others disastrous.

What You’ll Learn

By the end of this chapter, you will be able to:

List the controls of India’s climate and explain the monsoon with the thermal, ITCZ and jet-stream concepts
Give the IMD normal dates of onset and withdrawal (revised in 2020) and trace the Arabian Sea and Bay of Bengal branches
Explain active and break spells and why the timing of rain matters for paddy
Describe the four seasons and match local storms and winds (loo, mango showers, kalbaisakhi, western disturbances) to their regions
Use the Long Period Average and IMD categories to judge a monsoon, and map rainfall zones, gradients, variability and Koeppen climatic regions
Explain ENSO, the Southern Oscillation, the IOD and the MJO, and their record of effects on India up to the 2026 season
Write Mains answers on monsoon dependence and drought with a Chhattisgarh angle

Prerequisites

Physiography of India — the Himalaya, Western Ghats and plateaus that shape rainfall
Physical Geography of Chhattisgarh — the state’s relief, to apply the national picture locally

Learning Path

Follow the topics in this order:

graph TD
    A["1. Mechanism of the Monsoon
Climate controls, ITCZ, jet streams,
onset dates, branches, breaks"] --> B["2. Seasons of India
Cold, hot, rainy, retreating;
local storms and winds"]
    B --> C["3. Rainfall Distribution
LPA, IMD categories, zones,
variability, Koeppen regions"]
    C --> D["4. El Nino, La Nina and IOD
ENSO, indices, MJO,
record of effects on India"]
    D --> E["5. Quick Revision
One-page sheet"]
    E --> F["Next chapter:
Soils and Natural Vegetation"]

Topics in This Chapter

#	Topic	What it covers
1	Mechanism of the Indian Monsoon	Controls of climate; thermal and ITCZ concepts; westerly and easterly jets, Tibet, Somali jet, Mascarene High; normal dates (1 June, 8 July, 17 September, 15 October); two branches; breaks; withdrawal
2	Seasons of India	Cold weather and western disturbances; hot weather, loo, mango and blossom showers, kalbaisakhi; south-west monsoon; retreating monsoon, October heat, north-east monsoon, cyclones; six traditional seasons
3	Rainfall Distribution and Climatic Regions	LPA 1,160.1 mm (annual) and 868.6 mm (June–September); IMD categories; rainfall zones and gradients; extremes; rain shadow; variability; Koeppen types; Chhattisgarh’s pattern
4	El Niño, La Niña and the Indian Ocean Dipole	Walker circulation; El Niño and La Niña; Southern Oscillation and SOI; Niño 3.4, ONI and RONI; IOD; MJO; ENSO and Indian droughts up to 2026
—	Quick Revision	Every date, number and name on one page

Where It Is Asked

Paper	What to expect
Prelims P-I (Part 1, India GS)	Fact-based and statement-based MCQs: onset and withdrawal dates, jet streams, branches of the monsoon, local winds and storms, highest and lowest rainfall places, Koeppen types, El Niño/La Niña/IOD features. Match-the-following on local storms and regions is common
Mains P-V (GS-III), Geography of India	Short answers (western disturbances, break in monsoon, rain shadow, IOD) and longer answers (mechanism of the monsoon, rainfall variability and drought, ENSO and Indian agriculture)
Prelims P-I (Part 2, Chhattisgarh)	The national picture underlies state questions on Chhattisgarh’s climate, rainfall and agro-climatic zones: see Climate and Soils of Chhattisgarh

Exam focus

High-yield: the revised normal dates (8 July for the whole country; withdrawal 17 September to 15 October); LPA 87 cm (1971–2020); IMD categories; loo / mango showers / kalbaisakhi / Bardoli Chheerha; Koeppen types; El Niño vs La Niña vs positive IOD.
Common mistakes: using the old 15 July date or the old 88 cm LPA; putting mango showers in Bengal; saying every El Niño causes drought; reversing the positive IOD.
Chhattisgarh angle for Mains: rain from Bay of Bengal depressions along the monsoon trough; Bastar wettest, western plain (Kabirdham–Bemetara) driest in the lee of the Maikal range; rain-fed paddy and drought response in El Niño years such as 2026.

Quick Reference: The Chapter at a Glance

Item	Key point
Climate type	Tropical monsoon; Tropic of Cancer crosses northern Chhattisgarh
Onset over Kerala	1 June (normal)
Whole country covered	8 July (normal, revised 2020)
Withdrawal	Begins about 17 September (west Rajasthan); complete about 15 October
Jet streams	Westerly jet shifts north of the Himalaya before onset; tropical easterly jet forms in summer
Branches	Arabian Sea (stronger) and Bay of Bengal
Seasons	Cold (Dec–Feb), hot (Mar–May), SW monsoon (Jun–Sep), retreating (Oct–Nov)
Annual LPA	1,160.1 mm (1971–2020)
June–September LPA	868.6 mm (87 cm), about 75% of annual
Wettest / driest	Mawsynram / Leh and western Rajasthan
ENSO	El Niño (warm) usually weakens the monsoon; La Niña (cold) usually helps
IOD	Positive (western Indian Ocean warmer) helps the monsoon
2026 season	About 87% of LPA: deficient, in an El Niño year

Start Learning

Begin with the first topic:

→ Mechanism of the Indian Monsoon