Climate and monsoon

Why it matters

Every June, millions of farmers wait for the first heavy rain. When it comes on time, rivers fill and crops grow; when it fails, there is drought and prices rise. That is why the monsoon is often called the "real finance minister" of India.

• Weather is the condition of the air (temperature, rain, wind, humidity) at a place for a short time — a few hours or a day.
• Climate is the average weather of a large area over a long period, usually 30 years or more.

The word monsoon comes from the Arabic word mausim, meaning "season". A monsoon is a wind that reverses its direction with the season — it blows from sea to land in summer and from land to sea in winter. India's climate is called a tropical monsoon climate because these seasonal winds control its rain and its seasons.

In the Constable paper, this topic appears in the Indian Geography part of General Studies, mostly as one-line facts, local winds, match-the-following and short "why" statements.

Core concept

Level 1 — Elements and factors of climate

Weather and climate are described using five elements: temperature, air pressure, wind, humidity and precipitation (rain, snow, hail).

Why is Delhi very hot in May and cold in January, while Mumbai stays mild? Because of these factors:

Factor	How it works	Indian example
Latitude	Sun's rays are more direct near the equator, so it is hotter there	South India is warmer than Kashmir in winter
Altitude (height)	Temperature falls by about 6.5 °C for every 1,000 m of height	Shimla and Ooty are cooler than the plains below them
Distance from sea	The sea heats and cools slowly, so it keeps coastal places moderate	Mumbai has a mild (equable) climate; Delhi has an extreme (continental) climate
Pressure and winds	Winds always blow from high pressure to low pressure	Seasonal winds decide where and when it rains
Relief (mountains)	Mountains block winds and force moist air to rise and rain	The Himalayas stop cold Central Asian winds and trap monsoon winds

The Tropic of Cancer passes through the middle of India, so the north lies outside the tropics. Still, the whole country has a monsoon climate, because the Himalayas shut out cold northern winds and make the monsoon winds drop their rain here.

Level 2 — The four seasons

Season	Months	Main features
Cold weather (winter)	December – February	Dry north-east winds blow from land to sea; clear skies; cold north; rain/snow in the north-west from western disturbances; rain on the Tamil Nadu coast
Hot weather (summer)	March – May	Sun's rays become direct over north India; heat increases northwards; hot dry wind Loo; dust storms and local pre-monsoon showers
South-west monsoon (rainy)	June – September	Moist winds from the Indian Ocean; about three-fourths of India's yearly rain falls in this season
Retreating monsoon (post-monsoon)	October – November	Winds weaken and turn back; "October heat"; cyclones on the eastern coast; main rainy season of the Tamil Nadu coast

Winter rain in the north-west: Western disturbances are low-pressure systems that start over the Mediterranean Sea and travel east with the westerly winds. They bring light rain to Punjab, Haryana and nearby plains and snow to the Himalayas. This small winter rain is very useful for the rabi crop, especially wheat.

Pre-monsoon local winds and showers (summer):

Name	Region	Nature / use
Loo	Northern plains (Punjab to Bihar)	Hot, dry, dusty afternoon wind in May–June; can cause heatstroke
Mango showers	Kerala and coastal Karnataka	Pre-monsoon showers that help mangoes ripen early
Blossom (coffee) showers	Kerala and nearby coffee areas	Make coffee plants flower
Kalbaisakhi (Nor'westers)	West Bengal and Assam	Violent evening thunderstorms; name means "calamity of the month of Baisakh"; in Assam they are called Bardoli Chheerha and help tea, jute and rice

How the south-west monsoon works (the "why")

1. Unequal heating: In summer, land heats much faster than the sea. A strong low-pressure area forms over north-west India (the Thar region), while the Indian Ocean stays cooler with higher pressure.
2. Winds move: Air flows from the high-pressure ocean towards the low-pressure land.
3. They turn: The south-east trade winds of the southern hemisphere cross the equator. The Earth's rotation (Coriolis force) bends them to the right, so they reach India from the south-west — hence "south-west monsoon".
4. They carry moisture: Crossing the warm ocean, they fill with water vapour.
5. They rain: When they hit hills or rise over hot land, the air cools, vapour condenses and it rains.

Timing: The monsoon usually reaches the Andaman and Nicobar Islands in the second half of May. It reaches the mainland at Kerala around 1 June, often with a sudden heavy downpour called the "burst of the monsoon". It then spreads north and covers the whole country by about early-to-mid July. Withdrawal begins from north-west India (Rajasthan) in September and is slower and more gradual than the onset.

The two branches

The Indian peninsula splits the monsoon into two branches. The Arabian Sea branch is the stronger one.

	Arabian Sea branch	Bay of Bengal branch
Path	Strikes the Western Ghats; another part moves along the Narmada–Tapi valleys into central India; a third part moves over Gujarat and Rajasthan	Strikes the Myanmar and Bangladesh coasts, turns into north-east India, then is turned westward by the Himalayas along the Ganga plain
Key result	Very heavy rain on the west coast; little rain in Rajasthan because the Aravallis lie parallel to the wind and do not stop it	Funnel-shaped Garo–Khasi hills give Meghalaya the heaviest rain on Earth; rain decreases from east to west along the Ganga plain

Rainfall distribution

• Highest rain (over about 400 cm a year in parts): the west coast and north-east India. Mawsynram, near Cherrapunji (Sohra) in Meghalaya, gets the highest average annual rainfall in the world.
• Lowest rain (under about 60 cm): western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab; the interior Deccan east of the Western Ghats; and Ladakh (a cold desert).

Rain shadow: When moist wind climbs a mountain, the windward side gets heavy rain (orographic or relief rainfall). After crossing the top, the air sinks, warms up and can hold its moisture, so the far side gets little rain. This dry far side is called the leeward side or rain-shadow area. Mangaluru and Mumbai (windward) are very wet; Bengaluru and Pune (leeward, on the plateau) are much drier.

Why the Tamil Nadu coast is dry in June–September: it lies in the rain shadow of the Western Ghats for the Arabian Sea branch, and the coast runs parallel to the Bay of Bengal branch. It gets most of its rain in October–December, when the north-east winds pick up moisture over the Bay of Bengal.

Level 3 — Advanced ideas

• ITCZ and monsoon trough: The Inter-Tropical Convergence Zone is a low-pressure belt where trade winds meet. In July it shifts north to about 20°–25° N over the Ganga plain; here it is called the monsoon trough.
• Break in the monsoon: a dry spell of days or weeks during the rainy season. It happens when the monsoon trough moves close to the Himalayan foothills — the plains go dry while the hills get heavy rain.
• Jet streams: In winter a fast westerly jet stream blows south of the Himalayas and brings western disturbances. In summer it shifts north of the Himalayas, helping the monsoon set in.
• El Niño: an occasional warming of the Pacific Ocean off the coast of Peru (South America). El Niño years are usually linked with a weak monsoon in India, though not every time. La Niña (cooling there) is often linked with a good monsoon. A positive Indian Ocean Dipole (western Indian Ocean warmer than the eastern) usually helps the Indian monsoon.

Worked examples

Example 1 — Rain shadow.
Question: Mumbai receives far more rain than Pune, though Pune is not far away. Why?
Thinking: Both get the Arabian Sea branch. Mumbai is on the windward (sea-facing) side of the Western Ghats, where moist air rises and rains. Pune lies on the leeward side, where sinking air warms up and gives little rain.
Answer: Pune lies in the rain-shadow area of the Western Ghats.

Example 2 — Rain in the "wrong" season.
Question: Chennai gets most of its rain in which months, and from which winds?
Thinking: In June–September, the Tamil Nadu coast is in the rain shadow of the Arabian Sea branch and parallel to the Bay of Bengal branch. In October–December, north-east winds cross the Bay of Bengal, pick up moisture and hit the coast; cyclones also come then.
Answer: October–December, from the north-east (retreating) monsoon.

Example 3 — Winter rain for wheat.
Question: A farmer in Haryana gets a light rain in January that helps his wheat. What brings it?
Thinking: Winter winds over India are dry north-east winds, so it is not the monsoon; the rain comes from systems travelling from the west.
Answer: Western disturbances, which start over the Mediterranean Sea.

Example 4 — Arranging places.
Question: Arrange in decreasing order of monsoon rainfall: Delhi, Kolkata, Patna, Prayagraj.
Thinking: The Bay of Bengal branch moves west along the Ganga plain, losing moisture as it goes.
Answer: Kolkata > Patna > Prayagraj > Delhi.

Real-world connection

• Farming: Kharif crops (rice, cotton, maize) are sown with the onset of the south-west monsoon. Rabi crops (wheat, mustard, gram) are sown after it and use winter rain and stored water. A late or weak monsoon hurts both.
• Water and power: Monsoon rain fills reservoirs for drinking water, irrigation and hydroelectricity.
• Police duty: Constables are often first responders in floods, heatwaves and cyclone evacuations. Knowing that cyclones mostly hit the eastern coast in October–November, or that Loo is dangerous on May–June afternoons, helps in planning patrols and relief work.

How it is asked in the exam

With 200 questions in 180 minutes you get about 54 seconds per question. Climate questions are quick recall — aim for 20–30 seconds and save time for arithmetic.

Common formats:

• One-line fact: "The south-west monsoon first reaches mainland India at —" (Kerala).
• Local winds / match the following: Loo, Mango showers, Kalbaisakhi, western disturbances matched with regions or effects.
• Statement-based: two statements on branches, rain shadow or El Niño; choose "only I", "only II", "both" or "neither".
• Arrange in order: places by rainfall.

Difficulty levels:

• Easy: direct recall — origin of the word "monsoon", highest-rainfall place, months of a season.
• Medium: applying a cause — why Rajasthan is dry, why Pune gets less rain than Mumbai.
• Hard: two- or three-statement items mixing El Niño, jet streams and monsoon breaks, where one word makes a statement wrong. Example: (I) The Arabian Sea branch gives heavy rain to western Rajasthan. (II) The Aravallis lie parallel to this wind. Answer: only II is correct.

తెలుగు సారాంశం (Telugu summary)

భారతదేశ శీతోష్ణస్థితిని "ఉష్ణమండల రుతుపవన శీతోష్ణస్థితి" అంటారు. "మాన్సూన్" అనే పదం అరబిక్ పదం "మౌసిమ్" (రుతువు) నుంచి వచ్చింది; అంటే రుతువును బట్టి దిశ మార్చుకునే గాలులు.
వేసవిలో భూమి సముద్రం కంటే త్వరగా వేడెక్కి వాయవ్య భారతదేశంపై అల్పపీడనం ఏర్పడుతుంది. దాంతో హిందూ మహాసముద్రం నుంచి తేమతో కూడిన గాలులు నైరుతి దిశ నుంచి వీస్తాయి.
నైరుతి రుతుపవనాలు సాధారణంగా జూన్ 1 నాటికి కేరళ తీరాన్ని చేరుతాయి; సెప్టెంబర్‌లో వాయవ్య భారతదేశం (రాజస్థాన్) నుంచి వెనక్కి మళ్లడం మొదలవుతుంది.
వీటికి అరేబియా సముద్ర శాఖ, బంగాళాఖాత శాఖ అనే రెండు శాఖలు ఉన్నాయి; అరేబియా సముద్ర శాఖ బలమైనది.
పశ్చిమ కనుమల పవనాభిముఖ వైపు భారీ వర్షం కురుస్తుంది; అవతలి వైపు ఉన్న పుణె, బెంగళూరు వంటి ప్రాంతాలు వర్షచ్ఛాయ ప్రాంతాలు.
మేఘాలయలోని మౌసిన్‌రామ్ ప్రపంచంలోనే అత్యధిక సగటు వార్షిక వర్షపాతం పొందుతుంది; పశ్చిమ రాజస్థాన్, లద్దాఖ్ అతి తక్కువ వర్షం పొందుతాయి. ఆరావళి పర్వతాలు గాలికి సమాంతరంగా ఉండటం వల్ల రాజస్థాన్‌లో వర్షం తక్కువ.
శీతాకాలంలో మధ్యధరా సముద్రం నుంచి వచ్చే పశ్చిమ అలజడులు పంజాబ్, హర్యానాలకు వర్షం తెచ్చి గోధుమ (రబీ) పంటకు మేలు చేస్తాయి.
తమిళనాడు తీరానికి ఎక్కువ వర్షం అక్టోబర్–డిసెంబర్‌లో ఈశాన్య (తిరోగమన) రుతుపవనాల వల్ల వస్తుంది; ఈ కాలంలో బంగాళాఖాతంలో తుఫానులు తూర్పు తీరాన్ని తాకుతాయి.
వేసవి స్థానిక గాలులు: లూ (ఉత్తర మైదానాలు), మామిడి జల్లులు (కేరళ, కర్ణాటక), కాల్‌బైశాఖి (పశ్చిమ బెంగాల్, అస్సాం). ఎల్‌నినో సంవత్సరాల్లో రుతుపవనం సాధారణంగా బలహీనపడుతుంది.

Key terms (English — తెలుగు):

• Weather — వాతావరణం
• Climate — శీతోష్ణస్థితి
• Monsoon — రుతుపవనాలు
• South-west monsoon — నైరుతి రుతుపవనాలు
• North-east / retreating monsoon — ఈశాన్య / తిరోగమన రుతుపవనాలు
• Low pressure — అల్పపీడనం
• Rainfall — వర్షపాతం
• Rain-shadow area — వర్షచ్ఛాయ ప్రాంతం
• Windward side — పవనాభిముఖ వైపు
• Leeward side — పవనవిముఖ వైపు
• Western disturbances — పశ్చిమ అలజడులు
• Cyclone — తుఫాను