Climate

1. Climate vs Weather

Weather refers to the state of the atmosphere over a short period of time — hours or days. It changes rapidly. For example, today it may be sunny, tomorrow it may rain.

Climate refers to the average weather conditions of a place measured over a long period of time (30 years). It is far more stable and predictable. The elements that make up both weather and climate are the same: temperature, humidity, rainfall, sunshine, wind speed and direction, and cloudiness.

India's climate is often described as the "Monsoon type of climate." The word "monsoon" comes from the Arabic word mausim, meaning season. The monsoon refers to the seasonal reversal of wind direction during the year.

Unity in diversity: Despite India's vast size and geographic diversity — from Himalayan peaks to coastal plains — the monsoon binds the entire subcontinent in a single climatic rhythm. This is why the monsoon is called the unifying bond of India.

2. Factors Controlling India's Climate

India's climate is shaped by a combination of seven key factors:

(a) Latitude: India lies between the Tropic of Cancer (23.5 degrees N) and the equator in the south, and extends up to about 37 degrees N in the north. The Tropic of Cancer passes through the middle of India, dividing it into two halves. The southern half (tropical) remains warm throughout the year, while the northern half (sub-tropical and temperate) experiences a continental-type climate with wider temperature ranges.

(b) Altitude: As altitude increases, temperature decreases. The Himalayas in the north are cold and snowy even in summer, while the Deccan Plateau and coastal plains remain warm. The Himalayas act as a barrier preventing cold Central Asian winds from entering India, making winters milder than they would otherwise be.

(c) Pressure and Winds: The pressure and wind systems over India are strongly influenced by the large landmass to the north (Central Asia) and the warm Indian Ocean to the south. During winter, a high-pressure area develops over Central Asia, causing cold dry winds to blow outward. During summer, low pressure over the Indian subcontinent draws in moist winds from the ocean.

(d) Distance from the Sea (Continentality): Coastal areas experience a moderate climate because the sea heats and cools slowly (high specific heat). Inland areas far from the sea have an extreme or continental climate — very hot summers and very cold winters. Cities like Delhi and Nagpur experience a much wider temperature range than Mumbai or Chennai.

(e) Ocean Currents: The warm Indian Ocean on three sides of the peninsula raises the humidity of winds blowing over it. This moisture-laden air is the source of most of India's rainfall.

(f) Relief Features (Orographic Effect): Mountains and hills play a crucial role. When moisture-laden winds strike a mountain range, they are forced to rise. As they rise, they cool and cause orographic rainfall on the windward side. The leeward (rain-shadow) side receives very little rain. For example, the Western Ghats cause heavy rainfall on the west coast (Malabar Coast) but the Deccan Plateau behind them is dry.

(g) Upper Air Circulation (Jet Streams): Jet streams are fast-flowing, narrow air currents found in the upper atmosphere at heights of 7–12 km. The Sub-tropical Westerly Jet Stream blows over India in winter, responsible for western disturbances (bringing winter rain to north India). In summer, the jet stream shifts north of the Himalayas, allowing monsoon winds to dominate.

3. The Monsoon Mechanism

The monsoon is the most important climatic event for India. Understanding its mechanism requires looking at three interconnected phenomena:

(a) ITCZ — Inter-Tropical Convergence Zone: This is the equatorial trough (low-pressure belt) near the equator where Trade Winds from both hemispheres meet. Normally it lies near the equator, but during summer (July) it shifts northward to the Gangetic Plain due to intense heating of the land. This shift is crucial — it draws moisture-laden southwest winds deep into India. The ITCZ over the Gangetic Plain is sometimes called the monsoon trough.

(b) Jet Streams and Monsoon Onset: During winter, the Sub-tropical Westerly Jet Stream blows south of the Himalayas, keeping cold conditions in north India. By late May/early June, this jet stream retreats north of the Himalayas. Simultaneously, an Easterly Jet Stream (Tropical Easterly Jet) develops over the Indian Peninsula around 14 degrees N. This easterly jet accelerates the onset of the southwest monsoon and is responsible for the sudden, violent onset called the "Burst of Monsoon."

(c) Differential Heating of Land and Sea: Land heats up and cools down faster than the sea. During Indian summer (April–June), the landmass becomes intensely hot, creating a strong low-pressure system over the subcontinent. The Indian Ocean remains cooler (high pressure). Winds blow from high pressure (sea) to low pressure (land) — bringing moisture-laden air onshore. This is the fundamental driver of the Southwest Monsoon. In winter, the process reverses: land cools rapidly, creating high pressure, and dry winds blow from land to sea — this is the Northeast Monsoon.

(d) El Nino Effect: El Nino (meaning "the child" in Spanish) is a warm ocean current that appears in the eastern Pacific Ocean near Peru around December every few years. When El Nino is strong, it causes:

• Higher sea surface temperatures in the Pacific Ocean
• Weakening of trade winds globally
• Weakening of the Indian monsoon — leading to drought conditions in India
• Excess rainfall in parts of the Pacific region

A negative El Nino event is called La Nina, which tends to intensify the Indian monsoon, leading to above-normal rainfall. El Nino events occur irregularly, roughly every 2–7 years.

4. The Four Seasons of India

(a) Cold Weather Season (Winter) — December to February

• The sun shines vertically over the Tropic of Capricorn (southern hemisphere), so northern India receives oblique sunlight and experiences low temperatures.
• Temperature decreases from south to north. Chennai remains around 24–25 degrees C while Delhi drops to 5–10 degrees C.
• A high-pressure area develops over northern India; winds blow from north to south (from land to sea).
• The northeast trade winds pick up some moisture from the Bay of Bengal and cause rainfall in Tamil Nadu and Andhra Pradesh — called the Northeast Monsoon.
• Western Disturbances: Low-pressure systems from the Mediterranean Sea are carried by westerly jet streams across West Asia into northwest India. These bring winter rainfall to Punjab, Haryana, and Uttarakhand and snowfall in the Himalayas. This rain is crucial for Rabi crops (wheat).

(b) Hot Weather Season (Summer) — March to May

• The sun moves northward toward the Tropic of Cancer. Temperatures rise sharply across the subcontinent.
• Highest temperatures (45–48 degrees C) are recorded in Rajasthan, Punjab, and Haryana — the Thar Desert region.
• A strong low-pressure area builds over Rajasthan and the Indo-Gangetic Plain.
• Loo: Hot, dry, dusty winds called Loo blow over the northern plains from west to east during afternoon in May and June. They can be dangerous for human health.
• Dust Storms (Andhis): In Rajasthan and Punjab, dust storms occur in the afternoon, often followed by cooling and light rain.
• Nor'westers (Kalbaisakhi): In West Bengal and Assam, violent squalls blow from the northwest during late afternoons. Known as Kalbaisakhi in Bengali, they bring thunder, lightning, and heavy rainfall. They are beneficial for tea cultivation in Assam and jute in West Bengal.
• Mango Showers: Pre-monsoon showers in Kerala and Karnataka help in the early ripening of mangoes.

(c) Advancing Southwest Monsoon Season (Rainy Season) — June to September

• By early June, the southwest monsoon sets in over the Kerala coast (around June 1). This sudden and violent onset is called the Burst of Monsoon.
• The monsoon arrives in two branches:
  • Arabian Sea Branch: Strikes the Western Ghats first, causing very heavy rainfall on the west coast. It then crosses the Ghats (weakened) and brings less rain to the Deccan Plateau. Another sub-branch goes up the Arabian Sea into Gujarat and Rajasthan.
  • Bay of Bengal Branch: Moves up along the Bay of Bengal, enters northeast India (Assam, Meghalaya) and then turns west along the Himalayas, covering the Gangetic Plain progressively.
• Both branches converge and cover the whole of India by mid-July.
• Mawsynram (Meghalaya) near Cherrapunji receives the world's highest rainfall (about 1141 cm annually) due to orographic effect — moisture-laden Bay of Bengal winds hit the steep slopes of the Khasi Hills.

(d) Retreating Southwest Monsoon Season (Post-Monsoon / Autumn) — October to November

• By September, the monsoon begins to retreat from north India. The low-pressure trough over the Gangetic Plain weakens.
• Winds start reversing direction — the northeast trade winds pick up moisture from the Bay of Bengal and bring rain to the southeastern coast (Tamil Nadu, coastal Andhra Pradesh).
• October and November are hot and humid — this uncomfortable period is called "October Heat."
• Cyclonic depressions form in the Bay of Bengal and move northwest, bringing rain to the Coromandel coast. These tropical cyclones can be very destructive.
• By December, the monsoon has completely retreated and the cold weather season begins.

5. Onset and Variability of Monsoon

Onset of Monsoon: The monsoon does not arrive gradually — it comes with a "burst," bringing very heavy rainfall, thunder, and lightning almost overnight. The normal date of onset is June 1 over Kerala.

The monsoon advances northward, covering different parts at different times:

• June 1 — Kerala coast
• June 10–13 — Mumbai and Goa
• June 29 (normal) — Delhi
• Mid-July — Rajasthan and the rest of India

Variability: The monsoon is notoriously variable from year to year, causing:

• Droughts: When rainfall is significantly below normal (often linked to El Nino years).
• Floods: When rainfall is far above normal, causing rivers to overflow.
• Breaks in monsoon: During the monsoon season, there are "active" periods (heavy rain) and "break" periods (little or no rain for a week or more). Breaks occur when the monsoon trough shifts toward the Himalayas. During breaks, rainfall decreases over the plains but heavy rain continues in Himalayan foothills.
• Some years the monsoon is early (beneficial for kharif crops), other years it is late or fails.

6. Rainfall Distribution across India

Rainfall in India is extremely uneven — some areas are among the rainiest in the world, while others are near-desert conditions.

High Rainfall (above 200 cm annually):

• Western Coast (Konkan and Malabar Coast): The Arabian Sea branch of the monsoon strikes the Western Ghats head-on. Mumbai receives about 200 cm; some Ghats slopes receive over 400 cm.
• Northeast India: Mawsynram and Cherrapunji (Meghalaya) receive the world's highest rainfall — about 1141 cm at Mawsynram. Assam, Meghalaya, Manipur, and Mizoram receive 200+ cm annually.
• Sub-Himalayan belt in West Bengal and Sikkim also receives very heavy rain.

Moderate Rainfall (100–200 cm):

• Most of the Gangetic Plain (UP, Bihar, West Bengal plains)
• Eastern Madhya Pradesh, Odisha, and southern parts of peninsular India

Low Rainfall (50–100 cm):

• Interior Deccan Plateau (rain-shadow zone of Western Ghats)
• Eastern Rajasthan, parts of Haryana and Punjab, and western UP

Very Low Rainfall (below 50 cm — semi-arid or arid):

• Rajasthan (Thar Desert): Less than 25 cm in many areas. Jaisalmer receives as little as 9 cm per year. The Aravalli Mountains run parallel to the Arabian Sea branch and do not block moisture from reaching Rajasthan (the branch flows parallel to and then over the Aravallis).
• Leh (Ladakh): Cold desert — less than 10 cm annually. Located in the rain-shadow of the Himalayas; both monsoon branches are blocked.
• Parts of Kutch in Gujarat also receive very low rainfall.

Special Note — Tamil Nadu: The east coast (Coromandel Coast) receives most of its rain during the retreating monsoon (October–December) from the northeast monsoon, not the southwest monsoon. During the southwest monsoon, Tamil Nadu lies in the rain-shadow zone of the Eastern Ghats.

7. Monsoon — The Unifying Bond of India

The monsoon is not just a meteorological event — it is a cultural, agricultural, and social phenomenon that unites the entire country.

• Agricultural lifeline: About 70% of India's annual rainfall comes from the southwest monsoon (June–September). The entire calendar of Kharif crops (rice, jowar, bajra, cotton, groundnut) is tied to the monsoon's arrival.
• Rivers and water: All major Indian rivers (Ganga, Brahmaputra, Godavari, Krishna, Narmada) are fed primarily by monsoon rainfall. Reservoirs, groundwater, and irrigation systems all depend on monsoon recharge.
• Cultural celebration: The arrival of monsoon is celebrated across India — Teej festivals in Rajasthan, boat races in Kerala, and folk songs across regions celebrate the first rains. Kalidasa's Meghaduta ("The Cloud Messenger") is a famous Sanskrit poem celebrating the monsoon.
• Economic impact: A good monsoon boosts agricultural output, raises rural incomes, increases consumer spending, and positively affects the entire economy. A failed monsoon can cause drought, economic slowdown, and distress migration.
• Common experience — the unifying bond: Despite differences in language, culture, religion, and geography, all Indians wait for and depend on the same monsoon. Farmers from Kerala to Punjab, from Assam to Rajasthan, look to the sky in June with the same hope and anxiety. This shared dependence is what makes the monsoon India's unifying bond.

8. Climate Regions of India

Based on temperature, rainfall, and seasonal patterns, India has several distinct climate regions:

(a) Tropical Rainforest Climate: Western slopes of the Western Ghats, Andaman and Nicobar Islands, and parts of northeast India. Heavy rainfall throughout the year (over 200 cm), high temperature, and high humidity. Dense evergreen forests.

(b) Tropical Savanna (Monsoon) Climate: Most of peninsular India (excluding rainforest areas). Distinct wet (monsoon) and dry seasons. Rainfall 75–150 cm, concentrated in 4–5 months. Temperature high throughout the year. This is the most widespread climate type in India.

(c) Tropical Semi-Arid (Steppe) Climate: Interior Deccan Plateau — rain-shadow zone of the Western Ghats. Rainfall 40–75 cm. Dryland farming, millets, and pulses are grown here. Parts of Karnataka, Maharashtra, and Andhra Pradesh.

(d) Tropical and Sub-Tropical Arid and Desert Climate: Western Rajasthan (Thar Desert) and Rann of Kutch. Rainfall below 25 cm, extreme heat in summer, cold nights in winter. Sparse thorny vegetation; wildlife includes the desert fox and Indian bustard. Longest summer days due to northerly latitude.

(e) Humid Sub-Tropical Climate (with dry winters): Northern Plains — Punjab, Haryana, Uttar Pradesh, Bihar. Hot summers, cold winters, moderate rainfall (60–100 cm) mainly in monsoon season. Western disturbances bring important winter rain for Rabi crops.

(f) Mountain (Alpine) Climate: Himalayas and northeastern hill ranges. Temperature and rainfall vary sharply with altitude. Perpetual snow above 5000 m. Lower slopes have temperate forest. Leh and Ladakh experience cold desert conditions — very little rainfall and extreme cold.

9. NCERT Exercises — Fully Solved

Q1. What are the controls affecting the climate of India?

Answer: The six major controls are: (i) Latitude — the Tropic of Cancer divides India into tropical (warmer) and subtropical zones; (ii) Altitude — higher areas are cooler; the Himalayas protect India from cold north-Asian winds; (iii) Pressure and winds — seasonal reversal of wind direction drives the monsoon; (iv) Distance from the sea — coastal areas have moderate climate, interiors have extreme climate; (v) Ocean currents — warm Indian Ocean keeps coastal climates moist and humid; (vi) Relief features — mountains cause orographic rainfall on windward side and rain-shadow on leeward side; (vii) Jet streams (upper air circulation) — western disturbances in winter; easterly jet triggers monsoon onset.

Q2. Why does India have a monsoon type of climate?

Answer: India has a monsoon type of climate because of its location in the tropical and sub-tropical zone, surrounded by the Indian Ocean on three sides. The dominant control is the seasonal reversal of winds — the southwest monsoon in summer (driven by intense low pressure over the hot landmass pulling in ocean air) and northeast winds in winter (land cools, high pressure pushes winds out to sea). The ITCZ migration to the Gangetic Plain, the retreat of the Westerly Jet Stream and the emergence of the Easterly Jet Stream in summer, and the Himalayan barrier all reinforce this classical monsoon pattern. The entire agricultural, economic, and cultural life of India follows this monsoon rhythm.

Q3. Which part of India does not have a well-defined hot weather season?

Answer: The peninsular coast and extreme south India do not have a well-defined hot weather season. Coastal areas receive sea breezes that moderate temperatures year-round. Temperatures rarely cross 38 degrees C on the coast. In contrast, interior north India experiences intense summer heat (45–48 degrees C) with a very distinct hot season from March to May. The moderating influence of the surrounding seas prevents a sharp hot season in peninsular India.

Q4. Why do the monsoon winds change direction?

Answer: The change in direction of monsoon winds is due to: (i) Differential heating of land and sea — land heats up and cools faster than the sea. In summer, intense low pressure forms over land, drawing moist ocean winds inward (southwest monsoon). In winter, high pressure over land pushes winds outward toward the sea (northeast winds). (ii) Coriolis force — deflects winds to the right in the Northern Hemisphere, causing the incoming winds to approach from the southwest. (iii) Seasonal shift of ITCZ and jet streams — the northward shift of the ITCZ and the replacement of the westerly jet by the easterly jet over the peninsula in summer trigger and amplify the reversal.

Q5. What is the "burst of the monsoon"? What do you understand by "breaks" in the monsoon?

Answer: The "burst of monsoon" refers to the sudden onset of monsoon rains characterised by extremely heavy rainfall, thunder, and lightning — not a gradual increase but a violent downpour as if the sky has "burst" open. It first occurs over Kerala around June 1. Breaks in monsoon are periods of little or no rainfall during the rainy season, lasting a week or more. Breaks occur when the monsoon trough (ITCZ) shifts northward toward the Himalayas — rainfall decreases over the plains but heavy rain continues in the Himalayan foothills. A prolonged break can cause drought conditions in the affected parts of India.

Q6. Define "October Heat."

Answer: After the retreat of the southwest monsoon in October–November, the northern plains become oppressively hot and humid. The sky is clear of clouds but the land remains moist after months of heavy rain. High temperatures combined with high humidity create very uncomfortable conditions. This uncomfortable transition period, between the end of the rainy season and the onset of cool winter, is called "October Heat."

Q7. Why does Mawsynram receive the highest rainfall in the world?

Answer: Mawsynram (near Cherrapunji in Meghalaya) receives the world's highest average annual rainfall (~1141 cm) due to the orographic (relief) effect. The Bay of Bengal branch of the southwest monsoon moves northeastward and hits the steep southern slopes of the Khasi and Jaintia Hills (Meghalaya). The funnel-shaped topography concentrates and forces the moisture-laden air upward rapidly; the air cools and condenses, producing exceptionally intense and prolonged rainfall. The hills act as a wall that traps and uplifts the moist ocean air.