Climate and Rainfall of India: Monsoon, Seasons and PYQs
Climate of India notes for exams: the monsoon mechanism, four seasons, onset and retreat, rainfall distribution, local storms and El Nino effects.
By GK24 Editorial Team· Published · 4 min read
India has a tropical monsoon climate, named from the Arabic word mausim, meaning season, because its winds reverse direction between summer and winter. The whole agricultural year, the filling of reservoirs and a large part of the economy turn on a rainy season of about four months. Because the country stretches from the Himalaya to the sea and from the desert to the rainforest, almost every climatic type is found within it, and examiners test both the mechanism of the monsoon and the names of its local winds.
Why India has a monsoon climate
The Tropic of Cancer passes through the middle of the country, so the south is tropical and the north lies in the sub-tropical belt. The Himalaya blocks the cold winds of Central Asia and holds the monsoon winds over the plains, which is why north India is warmer in winter than places at the same latitude in western Asia. In summer the intense heating of the Thar desert and the northern plains creates a low pressure trough, while high pressure sits over the southern Indian Ocean. Air moves from the high to the low, and the south-east trade winds of the southern hemisphere cross the equator, turn right under the Coriolis force and arrive as the south-west monsoon. The shifting of the Inter Tropical Convergence Zone northwards, the heating of the Tibetan plateau and the position of the tropical easterly jet stream over peninsular India are the other elements of the mechanism.
The four seasons
| Season | Months | Main features |
|---|---|---|
| Winter | December to February | Clear skies, low humidity, rain in the north-west from western disturbances and in Tamil Nadu from the retreating monsoon |
| Summer | March to May | Rising temperature, the loo in the northern plains, local storms such as Kal Baisakhi and mango showers |
| South-west monsoon | June to September | The rainy season, about three-quarters of the annual rainfall, with breaks in the monsoon |
| Retreating monsoon | October to November | October heat, cyclones on the eastern coast, north-east monsoon rain in Tamil Nadu |
The south-west monsoon normally reaches Kerala about the first of June, the burst of the monsoon. It then advances in two branches, the Arabian Sea branch and the Bay of Bengal branch, which meet over the north-western plains. The Bay branch is deflected westwards by the Himalaya and moves up the Ganga valley, which is why rainfall in the plains falls from east to west. The monsoon begins to withdraw from north-western India in early September and leaves the southern peninsula by December. During the retreat the winds blow from land to sea, pick up moisture over the Bay of Bengal and give the Coromandel coast of Tamil Nadu its main rainfall, called the north-east or retreating monsoon.
How rainfall is distributed
The average annual rainfall of India is about 125 centimetres, but the distribution is very uneven. Mawsynram and Cherrapunji in the Khasi hills of Meghalaya receive the heaviest rainfall in the country because the funnel shaped hills force the moist Bay branch to rise. The windward side of the Western Ghats, the coastal plain of Kerala and Karnataka, the north-eastern states and the sub-Himalayan belt of West Bengal get over 200 centimetres. The Deccan plateau east of the Ghats and eastern Rajasthan get between 60 and 100 centimetres because they lie in the rain shadow. Western Rajasthan, the Kutch region of Gujarat and the cold desert of Ladakh get under 60 centimetres. A line joining places of equal rainfall on a map is called an isohyet, as a line of equal pressure is an isobar and a line of equal temperature an isotherm.
Local storms and winds
- Loo: a hot, dry and strong afternoon wind of the northern plains in May and June, which can cause heat stroke.
- Kal Baisakhi or Norwesters: violent evening thunderstorms of West Bengal, Bihar, Jharkhand and Assam in the pre-monsoon months, useful for jute and rice.
- Mango showers: pre-monsoon showers in Kerala and coastal Karnataka that help mangoes ripen.
- Blossom showers or cherry blossom: pre-monsoon showers in Karnataka that help the coffee flowers bloom.
- Bardoli Chheerha: the name given to pre-monsoon showers in Assam.
- October heat: the oppressive, humid weather of the retreating monsoon in the northern plains.
Western disturbances, El Nino and La Nina
Western disturbances are low pressure systems that form over the Mediterranean region and travel eastwards with the westerly jet stream. They bring winter rain and snow to Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana and western Uttar Pradesh, and that rain is valuable for the rabi crop, especially wheat. El Nino is the periodic warming of the surface water of the eastern and central Pacific Ocean off the coast of Peru; it usually weakens the Indian monsoon and is associated with deficient rainfall. La Nina is the opposite, cooler than normal Pacific water, and is usually associated with a good monsoon. The Indian Ocean Dipole, the difference in surface temperature between the western and eastern Indian Ocean, also affects the strength of the monsoon. Within the season a spell of several dry days is called a break in the monsoon, and it is a break at the wrong moment, rather than the annual total, that ruins a crop.
Exam Point of View
Three kinds of question come from this topic. First, the mechanism: which wind, which pressure belt, which jet stream, which branch of the monsoon. Second, the names of local winds and storms, where Kal Baisakhi, loo, mango shower, blossom shower and Bardoli Chheerha must be matched to their regions. Third, rainfall figures and terms, where isohyet, the wettest place, the rain shadow of the Western Ghats and the rainfall of Rajasthan are asked. The standard traps are giving the south-west monsoon for the winter rain of Tamil Nadu, mixing the isohyet with the isobar, placing the blossom shower in Meghalaya instead of Karnataka, and reversing the effects of El Nino and La Nina.
Important Facts
| Climate type | Tropical monsoon; monsoon from the Arabic mausim, meaning season |
|---|---|
| Onset over Kerala | About 1 June, known as the burst of the monsoon |
| Branches of the monsoon | Arabian Sea branch and Bay of Bengal branch |
| Withdrawal | Begins from north-west India in early September |
| Rainy season share | About three-quarters of the annual rainfall in four months |
| Average annual rainfall | About 125 centimetres for the country as a whole |
| Wettest area | Mawsynram and Cherrapunji in the Khasi hills, Meghalaya |
| Driest areas | Western Rajasthan, Kutch and Ladakh, under 60 centimetres |
| Line of equal rainfall | Isohyet |
| Winter rain of Tamil Nadu | North-east or retreating monsoon, October to December |
| Winter rain of north-west India | Western disturbances from the Mediterranean region |
| Local storms | Loo, Kal Baisakhi, mango shower, blossom shower, Bardoli Chheerha |
| El Nino | Warming of the eastern Pacific; usually weakens the monsoon |
| Break in the monsoon | A dry spell within the rainy season |
Practice MCQs on this topic
What causes rainfall on the coastal areas of Tamil Nadu in the beginning of winters?
- A.North-Eastern Monsoon
- B.Local Air Circulation
- C.Temperate Cyclones
- D.South-West Monsoon
Show answer
As the monsoon retreats in October and November the wind direction reverses and air moves from the land towards the sea.
Read the full explanation →In which state of India is the rain caused by a lightning storm called Cherry Blossom?
- A.Gujarat
- B.Meghalaya
- C.Uttarakhand
- D.Karnataka
Show answer
The pre-monsoon thundery showers of Karnataka are called cherry blossom showers or blossom showers because they help the coffee plants of the Kodagu, Chikkamagaluru and Hassan belt to flower.
Read the full explanation →In India, during October-November, with the apparent movement of the sun towards the south, the ______ over the northern plains becomes weaker.
- A.Upper level trough
- B.Monsoon trough
- C.Lee trough
- D.Inverted trough
Show answer
The monsoon trough is the belt of low pressure that lies across the northern plains during the rainy season and guides the depressions that bring rain.
Read the full explanation →The line joining the areas having the same rainfall is called:
- A.Isobar
- B.Isohyet
- C.Isotherm
- D.Isohaline
Show answer
An isohyet is a line drawn on a map through all the places that receive the same amount of rainfall in a given period.
Read the full explanation →Which of the following pairs of type of climate and area is NOT correct? I. Semi-arid steppe climate - Punjab. II. Monsoon with dry summer - Coromandel coast of Tamil Nadu.
- A.Only I
- B.Neither I nor II
- C.Only II
- D.Both I and II
Show answer
In the Koeppen classification as applied to India, the semi-arid steppe climate marked BShw covers parts of Punjab, Haryana, western Uttar Pradesh and the drier interior of the peninsula, where rainfall is low but not as low as in a true desert.
Read the full explanation →The south-west monsoon normally reaches the coast of Kerala on about which date?
- A.1 April
- B.1 May
- C.1 June
- D.1 July
Show answer
The south-west monsoon normally sets in over the Kerala coast about the first of June, and the sudden heavy downpour that marks its arrival is called the burst of the monsoon.
Read the full explanation →Which place in India receives the highest average annual rainfall?
- A.Mawsynram in Meghalaya
- B.Agumbe in Karnataka
- C.Amboli in Maharashtra
- D.Pasighat in Arunachal Pradesh
Show answer
Mawsynram lies in the Khasi hills, and the neighbouring Cherrapunji, now called Sohra, stands close behind it.
Read the full explanation →The violent pre-monsoon evening thunderstorms of West Bengal and Assam are known as:
- A.Loo
- B.Kal Baisakhi
- C.Mango shower
- D.Blossom shower
Show answer
These are the violent evening thunderstorms of the months before the monsoon in West Bengal, Bihar, Jharkhand and Assam, and the name means the calamity of the month of Baisakh because the squalls can flatten huts and trees.
Read the full explanation →The winter rainfall of Punjab, Haryana and western Uttar Pradesh is caused by:
- A.The retreating monsoon
- B.Tropical cyclones of the Bay of Bengal
- C.Western disturbances
- D.The Arabian Sea branch of the south-west monsoon
Show answer
These are low pressure systems, that is temperate cyclones, which form over the Mediterranean and the Caspian region and travel eastwards with the westerly jet stream.
Read the full explanation →El Nino, which is usually linked with a weak Indian monsoon, refers to the warming of the surface waters of which ocean?
- A.The Atlantic Ocean
- B.The Pacific Ocean
- C.The Indian Ocean
- D.The Arctic Ocean
Show answer
El Nino is the periodic warming of the surface water of the central and eastern Pacific off the coast of Peru and Ecuador, and the name, meaning the child, was given by fishermen because it appears around Christmas.
Read the full explanation →Frequently Asked Questions
Why does Tamil Nadu get rain in winter and not in the south-west monsoon?
The Coromandel coast lies in the rain shadow of the Western Ghats when the south-west monsoon blows, so the Arabian Sea branch has already lost its moisture before it crosses to the east. During the retreat of the monsoon in October and November the winds blow from land to sea, gather moisture over the Bay of Bengal and strike the coast, giving Tamil Nadu its main rainy season, called the north-east or retreating monsoon.
What is a break in the monsoon?
A break is a spell of several dry days in the middle of the rainy season, caused by the shifting of the monsoon trough. Rain stops over the plains while the foothills and the eastern coast may still get showers. Long breaks at the sowing or flowering stage damage crops even in a year whose total rainfall is normal, which is why the distribution of rain matters more than the total.
What is the difference between an isohyet, an isobar and an isotherm?
All three are lines drawn on a map joining places with the same value of a weather element. An isohyet joins places of equal rainfall, an isobar joins places of equal atmospheric pressure and an isotherm joins places of equal temperature. An isohaline joins places of equal salinity in the sea. Examiners ask this as a one-line match, so the four terms should be learnt together.
How do El Nino and La Nina affect India?
El Nino is an abnormal warming of the surface water of the central and eastern Pacific Ocean, and it shifts the rising air and the rain belt away from the Indian region, so monsoon rainfall is usually below normal. La Nina is the cooling of the same waters and is usually linked with a normal or above normal monsoon. The link is a tendency and not a rule, since the Indian Ocean Dipole and other factors also act on the season.
Why is north India warmer in winter than other places on the same latitude?
The Himalaya stands as a wall across the north and blocks the extremely cold winds that blow out of Central Asia in winter. The mountains also hold the monsoon winds within the subcontinent in summer so that they shed their rain here. Without this barrier the northern plains would have a much colder winter, like places at the same latitude in western and central Asia.
Sources
- Contemporary India II (Class X), chapter on climate — NCERT
- India: Physical Environment (Class XI), chapter on climate — NCERT
