Indian Climate: Monsoon, Seasons, Rainfall & Climate Phenomena

India’s climate is primarily classified as “tropical monsoon” type. Understanding the monsoon mechanism, seasons, and rainfall distribution is essential for Kerala PSC exams. Climate questions appear in nearly every graduate-level paper.

Factors Influencing India’s Climate

Factor	How it Affects
Latitude	Tropic of Cancer divides India into tropical (south) and subtropical (north)
Himalayas	Block cold Central Asian winds; trap monsoon moisture
Distribution of land and water	Differential heating drives monsoon winds
Distance from sea	Coastal areas are moderate; interior is extreme
Altitude	Temperature decreases ~6.5°C per 1,000 m rise
Relief/Topography	Western Ghats force orographic rainfall on windward side
Upper air circulation	Jet streams influence onset and withdrawal of monsoon

The Four Seasons of India

Season	Months	Key Features
Cold Weather (Winter)	December–February	NE monsoon winds; dry in most of India; Tamil Nadu gets rainfall
Hot Weather (Summer)	March–May	Rising temperatures; loo (hot winds) in north; pre-monsoon showers (mango showers in Kerala, Nor’westers/Kal Baisakhi in Bengal/Assam)
Advancing Monsoon (Rainy)	June–September	SW monsoon; bulk of India’s rainfall (about 75% of annual total)
Retreating Monsoon (Autumn)	October–November	Monsoon withdraws from NW to SE; cyclones in Bay of Bengal; NE monsoon brings rain to Tamil Nadu

The Southwest Monsoon — Mechanism

Key Concepts

Concept	Explanation
Differential heating	Land heats faster than sea in summer, creating low pressure over northern plains
ITCZ shift	Inter-Tropical Convergence Zone shifts northward to Ganga plains in summer
Trade winds	SE trade winds from Southern Hemisphere cross equator, deflect right (Coriolis force), become SW monsoon
Somali Jet / Low-Level Jet	Strong wind current crossing Arabian Sea; drives moisture to India
Tibetan Plateau heating	Creates upper-level high pressure; helps establish the monsoon circulation
Tropical Easterly Jet	Upper atmosphere jet stream over peninsular India during monsoon

Two Branches of SW Monsoon

Branch	Route	Areas Receiving Rainfall
Arabian Sea Branch	Hits Western Ghats first; one arm goes to Gujarat/Rajasthan; one to central India	Kerala (June 1), Karnataka, Maharashtra, Gujarat
Bay of Bengal Branch	Enters NE India (Meghalaya); deflected westward by Himalayas along Ganga plain	NE India, Bihar, UP, Punjab

Monsoon Timeline

Date (Approximate)	Event
June 1	SW monsoon arrives in Kerala (onset)
June 10	Reaches Mumbai
June 15	Covers most of South and Central India
July 1	Covers eastern India
July 15	Reaches all of India including NW
September 1	Begins retreat from NW India
October 15	Withdraws from most of northern India
December	Fully withdrawn from India

PSC Note: June 1 is the normal date of monsoon onset over Kerala. This is the single most tested date in Indian geography.

The Northeast Monsoon (Retreating Monsoon)

Feature	Detail
Period	October–December
Wind direction	Northeast to Southwest
Moisture source	Bay of Bengal
Main beneficiary	Tamil Nadu and parts of Andhra Pradesh
Why Tamil Nadu?	Coast lies parallel to NE winds; winds pick up moisture over Bay of Bengal
Cyclone season	October–November cyclones in Bay of Bengal

Rainfall Distribution

Annual Rainfall Zones

Zone	Rainfall (cm/year)	Areas
Heavy rainfall (over 200 cm)	Western Ghats windward side, NE India (Meghalaya), Andaman-Nicobar	Cherrapunji, Mawsynram, Western coast
Moderate rainfall (100–200 cm)	Eastern plains, western coastal areas, parts of UP, Bihar, Bengal	Most of peninsular India
Low rainfall (50–100 cm)	Interior Deccan, parts of central India, Punjab, Haryana	Rain shadow regions
Very low rainfall (below 50 cm)	Western Rajasthan (Thar), Ladakh, parts of Gujarat	Arid/semi-arid zones

Rainfall Records

Record	Place	Detail
Wettest place (world, average annual)	Mawsynram (Meghalaya)	~11,871 mm average annual
Second wettest / most rain in a single year	Cherrapunji (Sohra)	Held the record once; now second to Mawsynram
Driest in India	Leh (Ladakh)	About 10 cm per year

Why Meghalaya gets so much rain: The funnel-shaped hills of the Khasi and Jaintia ranges force the Bay of Bengal branch of the monsoon sharply upward, causing intense orographic rainfall.

Climate Regions of India (Koppen Classification)

Type	Code	Areas	Features
Tropical Wet (Rainforest)	Af	Western coast, NE India, Andaman	Heavy rain throughout year
Tropical Monsoon	Am	Most of Western Ghats, West Bengal	Seasonal heavy rain, short dry season
Tropical Wet and Dry (Savanna)	Aw	Most of peninsular India	Distinct wet and dry seasons
Semi-arid (Steppe)	BSh	Rajasthan, Gujarat, parts of Karnataka, TN	Low rainfall, hot
Hot Desert	BWh	Western Rajasthan (Thar)	Very low rainfall, extreme heat
Humid Subtropical	Cwa	Northern plains (UP, Bihar, Punjab, Haryana)	Hot summers, cold winters, monsoon rain
Montane/Alpine	H	Himalayas, high-altitude areas	Cold, varies with altitude

Important Local Winds and Weather Phenomena

Phenomenon	Region	Description
Loo	Northern plains (UP, Rajasthan, Punjab)	Hot, dry summer winds (May–June)
Mango Showers	Kerala, Karnataka	Pre-monsoon showers in April–May helping mango ripening
Cherry Blossoms / Blossom Showers	Karnataka (coffee-growing areas)	Pre-monsoon showers helping coffee flowering
Nor’westers / Kal Baisakhi	West Bengal, Assam	Violent thunderstorms in April–May; beneficial for tea and jute
Bardoli Chheerha	Assam	Pre-monsoon thundershowers
October Heat	Northern India	Oppressive heat and humidity during retreating monsoon
Western Disturbances	North India (Punjab, J&K, HP)	Winter rainfall caused by Mediterranean weather systems traveling eastward

El Nino and La Nina

El Nino (ENSO — El Nino Southern Oscillation)

Feature	Detail
What it is	Periodic warming of sea surface temperature (SST) in central and eastern tropical Pacific Ocean
Normal condition	Warm water in western Pacific (near Indonesia); cold water in eastern Pacific (near Peru)
During El Nino	Warm water shifts to eastern Pacific; trade winds weaken
Effect on Indian monsoon	Generally weakens the SW monsoon, leading to drought or below-normal rainfall
Frequency	Every 2–7 years
Name meaning	”The Christ Child” (usually appears around Christmas off Peru’s coast)

La Nina

Feature	Detail
What it is	Abnormal cooling of SST in eastern Pacific
Effect on Indian monsoon	Generally strengthens the SW monsoon, leading to above-normal or heavy rainfall
Relation to El Nino	Opposite phase of ENSO cycle
Name meaning	”The Girl”

Indian Ocean Dipole (IOD)

Feature	Detail
What it is	Difference in SST between western and eastern Indian Ocean
Positive IOD	Western Indian Ocean warmer; enhances Indian monsoon rainfall
Negative IOD	Eastern Indian Ocean warmer; weakens Indian monsoon
Interaction	Positive IOD can counteract El Nino’s negative impact on Indian monsoon

Jet Streams and Indian Monsoon

Jet Stream	Season	Location	Effect
Subtropical Westerly Jet	Winter	South of Himalayas (over northern plains)	Brings western disturbances; winter rain in north India
Tropical Easterly Jet	Summer (monsoon)	Over peninsular India (at about 14°N)	Associated with strong SW monsoon

Key fact: The onset of SW monsoon coincides with the withdrawal of the Subtropical Westerly Jet from over northern India and the establishment of the Tropical Easterly Jet.

Climate Change and India

Observation	Detail
Temperature trend	Average temperature has risen by about 0.7°C over the past century
Monsoon trend	Increased variability; more extreme rainfall events
Glaciers	Himalayan glaciers retreating
Sea level	Rising about 1.3 mm per year along Indian coast
Extreme events	Increasing frequency of cyclones, floods, and droughts

Frequently Asked PSC Questions

Q: Normal date of monsoon onset over Kerala? A: June 1

Q: Wettest place in the world? A: Mawsynram, Meghalaya

Q: Which state gets rainfall from NE monsoon? A: Tamil Nadu (also parts of Andhra Pradesh)

Q: What is Loo? A: Hot dry winds blowing in northern plains during summer

Q: El Nino effect on Indian monsoon? A: Weakens the monsoon (leads to drought/below-normal rainfall)

Q: Mango showers occur in which state? A: Kerala and Karnataka (pre-monsoon showers in April–May)

Q: About 75% of India’s annual rainfall is received during? A: Southwest monsoon season (June–September)

Q: Western disturbances bring rainfall to which region? A: North India (Punjab, J&K, HP) during winter

Q: Tropic of Cancer passes through how many Indian states? A: 8 states (Gujarat, Rajasthan, MP, Chhattisgarh, Jharkhand, West Bengal, Tripura, Mizoram)

Exam Tips

• June 1 (monsoon onset in Kerala) is the single most asked date — never forget it
• El Nino = drought, La Nina = excess rain — this one-line distinction scores marks
• Mawsynram vs Cherrapunji — PSC still asks “wettest place” — answer is Mawsynram (for average annual), not Cherrapunji
• Know the two branches of SW monsoon and which areas each covers
• Tamil Nadu’s NE monsoon rainfall is a frequently asked “exception” question
• The Tropic of Cancer passing through 8 states is asked as both “name them” and “how many”