These climate of India notes for OPSC/UPSC cover the controls of climate, the monsoon mechanism and theories, jet streams, El Niño and La Niña, the four seasons, local storms, rainfall distribution and the Köppen types, with a full section on Odisha's climate and cyclones. For OAS prelims the chapter yields steady questions on monsoon dates, rainfall patterns, jet streams and local winds, and for mains it supports answers on monsoon variability, ENSO, western disturbances, cyclones and climate impacts on agriculture.
Climate of India: Type and Controlling Factors
India has a tropical monsoon climate, marked by seasonal reversal of winds and a distinct wet and dry season, with great regional variety. The Tropic of Cancer divides the country into two nearly equal halves: the south is tropical and the north is sub-tropical or temperate, so India lies in both zones. The 18°C January isotherm is taken as the dividing line between the tropical and sub-tropical zones.
| Control | Effect on India |
|---|---|
| Latitude | Tropic of Cancer splits the country; the south is hot throughout the year |
| Altitude | Temperature falls about 6.5°C per 1,000 m; hill stations are cooler than the plains |
| Distance from the sea | Coastal places have an equable climate; interior places such as Amritsar have extremes |
| Relief | Himalayas block Central Asian cold winds; Western Ghats cause orographic rain; Thar heating creates low pressure |
| Pressure and winds | Seasonal reversal of winds; jet streams; western disturbances |
| Ocean currents and ENSO | El Niño and Indian Ocean Dipole modulate monsoon rainfall |
- Longitude is not counted as a climatic control; latitude, altitude, distance from sea, relief and winds are.
- The monsoon climate does not arise merely from tropical location, since India extends from 8°4′N to 37°6′N.
- South India has an equable climate with low diurnal and annual range, while extremes are found in the north-west.
Köppen Climate Types in India
| Type | Description and area |
|---|---|
| Amw | Monsoon with short dry season; west coast south of Goa |
| As | Monsoon with dry summer; Coromandel coast of Tamil Nadu |
| Aw | Tropical savanna; most of the Peninsular plateau, including Odisha |
| BShw | Semi-arid steppe; rain-shadow belt of the Peninsula and Punjab–Haryana |
| BWhw | Hot desert; western Rajasthan |
| Cwg | Monsoon with dry winter; Ganga plain and north-east |
| Dfc | Cold humid winter; Arunachal Pradesh |
| E | Polar or alpine type; higher Himalaya |
IMAGE (Map): Köppen climate regions of India
Labels: Amw, As, Aw, BShw, BWhw, Cwg, Dfc, E, Tropic of Cancer
Caption: Climatic regions of India according to Köppen.
Find it: NCERT Class 11 India Physical Environment Chapter 4, Figure 4.7
Monsoon Mechanism and Theories of the Monsoon
The word monsoon comes from the Arabic mausim, meaning season. It refers to the seasonal reversal of wind direction, caused by the differential heating of land and sea.
Thermal Concept (Halley)
Halley (1686) explained the monsoon as a large-scale land and sea breeze. In summer the land heats faster than the sea, low pressure develops over north-west India and the winds blow from the sea to the land. In winter the process reverses.
Dynamic Concept (Flohn)
Flohn explained the monsoon as the seasonal shift of the planetary wind and pressure belts, in particular the Inter-Tropical Convergence Zone (ITCZ). In July the ITCZ, also called the monsoon trough, lies over the Ganga plain, so the south-east trades cross the equator, are deflected to the right by the Coriolis force and blow as the south-west monsoon.
Modern Concept: Jet Streams, Tibet and ENSO
- The heating of the Tibetan plateau creates a strong upper-air heat source.
- The sub-tropical westerly jet withdraws north of the Himalaya in early June, and the tropical easterly jet develops over the Peninsula. This shift coincides with the sudden burst of the monsoon.
- El Niño and the Indian Ocean Dipole (IOD) change the strength of the monsoon each year.
| Concept | Proponent | Core idea |
|---|---|---|
| Early observation | Al Masudi | First account of the reversal of ocean currents and monsoon winds |
| Thermal | Halley | Differential heating of land and sea |
| Dynamic | Flohn | Seasonal migration of the ITCZ and pressure belts |
| Jet stream concept | Yin (Yeh) | Upper-air jet shift controls the burst |
| El Niño concept | Gilbert Walker, Berkeley | Walker circulation and Southern Oscillation |
The summer monsoon arises from intense heating of the north-western plains and the Tibetan plateau, the shift of the ITCZ to about 25°N, the cross-equatorial flow of the south-east trades, and the upper-air change in the jet streams. It is not explained by the Himalaya alone.
IMAGE (Diagram): Mechanism of the south-west monsoon
Labels: Tibetan plateau heating, ITCZ over the Ganga plain, south-east trades crossing the equator, Coriolis deflection, tropical easterly jet, westerly jet north of the Himalaya, Arabian Sea branch, Bay of Bengal branch
Caption: How the south-west monsoon is drawn into India.
Find it: NCERT Class 11 India Physical Environment Chapter 4, Figures 4.2 and 4.3
Onset, Branches and Withdrawal
The monsoon arrives first in Kerala around 1 June. It splits into two branches: the Arabian Sea branch, which is stronger and brings heavy rain to the windward Western Ghats, and the Bay of Bengal branch, which is drawn towards the low pressure over north India and brings rain to the north-east and the Ganga plain. By the revised IMD normal dates, the monsoon covers the whole country by about 8 July and begins withdrawing from west Rajasthan around 17 September, with withdrawal complete by about 15 October.
| Region | Approximate onset |
|---|---|
| Kerala | 1 June |
| West Bengal, Odisha, Assam | About 5 to 10 June |
| Mumbai | About 10 June |
| Uttar Pradesh, Bihar | Mid to late June |
| Delhi | Late June |
| West Rajasthan | Early July |
A break in the monsoon occurs when the monsoon trough shifts towards the Himalayan foothills, leaving the plains dry while the foothills and the north-east receive heavy rain.
- Western disturbances are steered by the westerly jet, not the easterly jet.
- La Niña generally favours a good monsoon; it does not mean the monsoon is unaffected.
- The westerlies blow between about 30° and 60° latitude in each hemisphere.
- The monsoon arrives in Kerala first and not in Assam.
Jet Streams and ENSO
Jet Streams
Jet streams are narrow, fast upper-tropospheric winds, flowing from west to east, embedded in the upper westerlies. They are geostrophic upper-air winds, not surface winds, and they do not themselves bring rain.
| Jet stream | Season | Effect |
|---|---|---|
| Sub-tropical westerly jet | Winter, flowing south of the Himalaya and split into two branches by the Himalaya and Tibetan plateau | Steers western disturbances into north-west India |
| Tropical easterly jet | Summer, over the Peninsula, around 14°N | Linked to the monsoon burst and its strength |
El Niño, La Niña and the Indian Ocean Dipole
- El Niño: periodic warming of the eastern equatorial Pacific, which weakens the Walker circulation. It is generally associated with a deficient Indian monsoon, though not every El Niño year causes drought.
- La Niña: cooling of the equatorial Pacific, generally favouring a good monsoon.
- ENSO: El Niño and La Niña are opposite phases of the El Niño Southern Oscillation.
- Indian Ocean Dipole: a positive IOD (warmer western Indian Ocean) favours the monsoon and can offset an El Niño.
The monsoon of 2015 was deficient in an El Niño year, but in 1997 a strong positive IOD helped the monsoon even in a strong El Niño year.
Four Seasons of India (IMD Classification)
| Season | Months | Key features |
|---|---|---|
| Cold weather (winter) | December to February | High pressure over north-west India, clear skies, dry outblowing winds; western disturbances bring rain and snow to the north-west; tropical NE monsoon winds |
| Hot weather (summer) | March to May | Rising temperatures and low pressure in the north-west; loo; local storms |
| South-west monsoon | June to September | About 75 per cent of annual rainfall |
| Retreating monsoon | October to November | Clear skies, October heat, cyclones in the Bay of Bengal; NE monsoon rain on the Tamil Nadu coast |
Winter and Western Disturbances
Winter has clear skies and dry, stable air under a high-pressure system. Western disturbances are extra-tropical cyclonic systems that originate over the Mediterranean region and are brought into India by the westerly jet. They give winter rain and snow to Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana and Uttarakhand, which is highly beneficial for rabi crops such as wheat. Their rainfall decreases from west to east. Cold waves in the north are due to the lack of maritime influence, proximity to the Himalaya and cold air masses.
Hot Weather Season and Local Storms
| Local wind or storm | Region | Notes |
|---|---|---|
| Loo | Northern plains from Punjab to Bihar | Hot, dry afternoon wind of May–June |
| Kalbaisakhi (Nor’wester) | West Bengal, Odisha, Assam region | Evening thunderstorms of April–May; beneficial for jute and rice |
| Bardoichila | Assam | The Assam version of the Nor’wester |
| Mango showers | Kerala and coastal Karnataka | Pre-monsoon showers that help ripen mangoes |
| Cherry blossom (coffee showers) | Karnataka and Kerala | Help the flowering of coffee |
Retreating Monsoon
From October the low-pressure trough moves south, the monsoon withdraws, skies clear, days are hot and humid (October heat) and nights are pleasant. Cyclonic depressions from the Bay of Bengal bring heavy rain to the Coromandel coast in October–December, and the north-east monsoon gives Tamil Nadu more than half of its annual rain.
IMAGE (Map): Normal withdrawal and onset lines of the monsoon
Labels: Kerala 1 June; Mumbai 10 June; Delhi late June; Rajasthan early July; withdrawal line 17 September; Bay of Bengal branch, Arabian Sea branch
Caption: Progress and withdrawal of the south-west monsoon.
Find it: IMD normal onset and withdrawal dates map; NCERT Class 11 India Physical Environment Chapter 4
Rainfall Distribution in India
| Zone | Rainfall | Areas |
|---|---|---|
| Very high | Over 200 cm | Western Ghats windward side, Meghalaya, Assam and Arunachal hills, Tripura |
| High | 100 to 200 cm | Odisha, Jharkhand, east Madhya Pradesh, Bengal plains, parts of the Ghats |
| Medium | 50 to 100 cm | Punjab, Haryana, Uttar Pradesh, Gujarat, Deccan interior |
| Low | Below 50 cm | Western Rajasthan, Ladakh, rain-shadow pockets of the Deccan |
- Mawsynram in the East Khasi Hills records the highest average annual rainfall in India. The funnel-shaped Garo–Khasi–Jaintia hills trap and lift the Bay of Bengal branch.
- Rain shadow areas: Pune, Bengaluru, Vidarbha and Leh lie on leeward slopes, while Mumbai and Mangaluru are windward.
- Rainfall in the Ganga plain decreases westwards, from Bengal to Punjab, and the monsoon lasts longer in the south than in the north.
- A rainy day in IMD terms is a day with 2.5 mm or more of rain in 24 hours.
- Rajasthan has the highest rainfall variability, and low-rainfall areas are more variable than high-rainfall areas.
Rainfall-sequence questions are common: Sahyadri over the Ganga delta, over eastern Uttar Pradesh, over northern Gujarat; or Kochi, Kolkata, Patna, Delhi from high to low. Think windward, then east to west, then rain shadow.
Mains Dimension: Monsoon, Climate Variability and Impacts
Why the Monsoon Matters
Over 75 per cent of India's rainfall falls in the monsoon, so it governs kharif output, reservoir levels, hydropower, rural incomes and inflation. India remains a thirsty land despite abundant rain because of rapid run-off, evaporation and the concentration of rainfall in a few months, along with high variability.
Monsoon Variability and Extremes
- Breaks and active spells cause floods in some regions and droughts in others in the same season.
- Heat waves: the IMD declares a heat wave at 40°C or more in the plains and 30°C or more in hills, with a departure from normal of 4.5°C or more.
- Extreme rainfall: intense short spells have grown more frequent, leading to urban floods.
- Cyclones: the Bay of Bengal is more cyclone-prone than the Arabian Sea, with peaks in April–May and October–November, and most cyclones strike the east coast.
Forecasting and Institutions
The IMD issues monsoon forecasts, and the Ministry of Earth Sciences launched the Monsoon Mission in 2012 to improve dynamic forecasts in collaboration with IITM Pune. Mission Mausam was launched in 2024 to strengthen weather and climate observation and forecasting.
Likely Mains Questions
- Explain the mechanism of the south-west monsoon with reference to the role of jet streams and the Tibetan plateau. (250 words)
- Discuss the impact of El Niño and the Indian Ocean Dipole on the Indian monsoon. (150 words)
- Why do western disturbances matter to north-west India's agriculture? (150 words)
- Why are Bay of Bengal cyclones more frequent and destructive on the east coast than Arabian Sea cyclones on the west coast? (250 words)
- Explain why India faces water stress despite adequate annual rainfall. (150 words)
In mains answers, move from mechanism to variability to impact to response. Use named examples such as the 1999 Odisha Super Cyclone, the Monsoon Mission of 2012 and the revised IMD dates.
Climate of Odisha: Odisha Angle
Odisha lies wholly south of the Tropic of Cancer and has a tropical monsoon climate of the Aw (tropical savanna) type. The coast is maritime, humid and equable, while the western interior is hotter, with a larger range of temperature.
| Season | Features in Odisha |
|---|---|
| Winter (December to February) | Mild and mostly dry; Daringbadi in Kandhamal, the Kashmir of Odisha, is among the coolest places |
| Summer (March to May) | Hot; Titlagarh in Bolangir and other places in western Odisha record the highest temperatures, often above 45°C; Nor’wester (Kalbaisakhi) thunderstorms bring relief |
| Monsoon (June to September) | Most of the rain, from the Bay of Bengal branch and low-pressure systems moving inland; onset about 5 to 10 June |
| Post-monsoon (October to November) | Cyclonic storms and heavy rain on the coast |
Cyclones in Odisha
The Odisha coast is highly prone to tropical cyclones because it lies on the Bay of Bengal, where cyclones form frequently, and because the low, wide coastal plain offers little resistance to storm surge.
| Cyclone | Year | Landfall |
|---|---|---|
| Super Cyclone | 29 October 1999 | Near Paradip; led to the creation of the Odisha State Disaster Management Authority (OSDMA) |
| Phailin | October 2013 | Near Gopalpur, Ganjam; large-scale evacuation limited deaths |
| Fani | May 2019 | Near Puri |
| Yaas | May 2021 | Northern Odisha coast |
| Dana | October 2024 | Near Bhitarkanika and Dhamra |
Mangroves of Bhitarkanika reduce the impact of storm surges but do not cause cyclones, which form over warm Bay of Bengal waters. After the 1999 Super Cyclone Odisha set up OSDMA, cyclone shelters and early warning systems, which became a model for disaster management.
During Phailin in 2013, Odisha evacuated about a million people before landfall, which sharply reduced the death toll compared with 1999.
Climate of India MCQ and PYQ Practice
In January, the isotherm taken as the basis for dividing India into tropical and sub-tropical zones is
- 21°C
- 18°C
- 12°C
- 15°C
Show answer
(b) - The 18°C January isotherm. IAS (Pre) 1997
The term monsoon originated from which language?
- Arabic
- Spanish
- Hindi
- English
Show answer
(a) - It comes from the Arabic mausim. MPPSC (Pre) 2013
In which of the following states does the monsoon arrive first?
- Assam
- West Bengal
- Maharashtra
- Kerala
Show answer
(d) - Kerala, around 1 June. UPPSC (Pre) 2006
Arrange the following states by ascending date of onset of the monsoon: I. Uttar Pradesh II. West Bengal III. Kerala IV. Rajasthan
- II, III, I, IV
- III, II, I, IV
- III, I, II, IV
- I, II, III, IV
Show answer
(b) - Kerala, West Bengal, Uttar Pradesh, Rajasthan. CDS 2010
Which one of the following causes rainfall in the north-western parts of India during winter?
- Cyclonic depression
- Retreating monsoon
- Western disturbances
- South-West monsoon
Show answer
(c) - Western disturbances. IAS (Pre) 2009
South Arcot and Ramanathapuram receive over 50 per cent of their annual rainfall from
- South-West Monsoon
- North-East Monsoon
- Bay of Bengal branch of the summer monsoon
- Western disturbances
Show answer
(b) - The north-east monsoon. CDS 2018
In which of the following places does the maximum rainfall in India occur?
- Shillong
- Tura
- Mawsynram
- Cherrapunji
Show answer
(c) - Mawsynram. SSC 2012
Which one of the following places does not fall on a leeward slope?
- Pune
- Bengaluru
- Leh
- Mangaluru
Show answer
(d) - Mangaluru is on the windward coast. CDS 2018