Monsoons are distinguished by abundant seasonal rainfall as well as consistent seasonal winds that switch direction with startling regularity. The name “monsoon” derives from the Arabic word “mausim,” which means “season.” For centuries, sailors used this term to describe a pattern of alternating winds that blow from the north-east for six months and from the south-west for the other six months across the Indian Ocean and Arabian Sea. In general, the seasonal wind shift is around 120°, which is generated mostly by the differential heating of land and ocean. This low pressure zone is characterised by the continual ascent of moist wind from the sea surface to the upper layers of the sky, where cooling causes the air to lose its ability to store as much moisture, resulting in precipitation.

The interaction between these two seasons, Advancing and Retreating monsoons, makes the monsoon a unique phenomena in India. Study more topics from Indian Geography and their types from UPSC point of view.

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What Is the Monsoon?

The monsoon, which is simply a seasonal reversal of wind direction, is responsible for the majority of the rainfall in India and several other regions of the world. During the summer, the Thar desert and adjacent portions of the northern and central Indian subcontinent heat up.A low-pressure zone forms over the subcontinent as a result of the fast solar heating, which occurs primarily between April and May. The moisture-laden breezes from the Indian Ocean rush in to fill the vacuum. The ITCZ also swings northwards towards the subcontinent, bringing monsoon rains to the mainland in the last week of May or the first week of June. The monsoon is split into two sections beyond Kerala: the Arabian Sea branch and the Bay of Bengal branch. By the first week of July, monsoon winds had reached virtually every part of India.

What Causes the Monsoon Season?

• Differential Heating: The monsoon season is primarily caused by differential heating between land and sea.
• Summer Heating: During summer, land surfaces heat up more quickly than oceans, creating a temperature difference.
• Low-Pressure Area: As land heats up, low-pressure areas form, drawing moist air from oceans towards the land.
• Winds Shift: The pressure difference causes a shift in wind patterns, with moist air being pulled from the Indian Ocean.
• Moisture Laden Air: The onshore winds bring moisture-laden air, leading to abundant rainfall over the affected regions.
• Monsoon Trough: The shift in wind patterns establishes a monsoon trough, a region of low pressure supporting sustained rainfall.
• Seasonal Reversal: The monsoon season exhibits a seasonal reversal of wind direction, impacting various parts of the world.
• Importance for Agriculture: The monsoon is crucial for agriculture, providing essential water for crops in affected regions.

Onset of the Monsoon in India for UPSC

• The monsoon usually comes in the first week of June near the southern tip of the Indian peninsula. It then splits into two branches, the Arabian Sea branch and the Bay of Bengal branch.
• The time from early to mid June when the first batch of Monsoon winds arrive on the western coast of the Indian peninsula is referred to as the Monsoon onset.
• The Arabian Sea branch arrives at Mumbai ten days later, on June 10th. By mid-June, the Arabian Sea branch of the monsoon had arrived over Saurashtra-Kachchh and the central section of the nation.
• The Bay of Bengal moves quickly and arrives in Assam in the first week of June. Monsoon winds are then diverted by high mountains and flow west over the Ganga plains.
• The monsoon branches of the Arabian Sea and the Bay of Bengal meet over the northern region of the Ganga plains.
• By the end of June, Delhi generally receives monsoon rains from the Bay of Bengal branch.
• By the first week of July, monsoon has arrived in western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan. By mid-July, the monsoon had reached Himachal Pradesh and the rest of the country.

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Retreating Monsoon Season for UPSC

• The clouds dissipate as the monsoons move away, and the sky clears. The temperature begins to drop precipitously during the day.
• Except for a few southern states, monsoon rains are waning across India. The monsoon trough is weakening and gradually shifting southward.
• Because of the retreating monsoons, the most severe and destructive tropical cyclones form in the Indian oceans, particularly in the Bay of Bengal.
• Winds blow from the north west to the south east and transport little moisture from the surface to the sea.
• It is beneficial in the production of Rabi crops.
• The monsoons leave the country’s extreme northwestern point in September, the peninsula in October, and the extreme south-eastern tip in December.
• The south-west monsoons arrive in Punjab in the first week of July and leave in the second week of September.
• The south-west monsoons arrive on the Coromandel coast in the first week of June and leave in the middle of December.
• In contrast to the abrupt burst of the advancing monsoons, the retreat is more gradual and takes roughly three months.

Branches of Indian Monsoon For UPSC

Arabian Sea branch:

• It is sometimes referred to as the South-West monsoon. This monsoon trough travels around the Arabian Sea.
• It moves quickly and arrives in the country’s northwestern and north-eastern regions in the first week of June.
• The Inter-Tropical Convergence Zone is a low-pressure zone in the equator where trade winds converge, and it is found about 20-25 degrees latitude in June (known as monsoon trough).
• As a result of this change, southern hemisphere trade winds blow from southwest to northwest and northeast. In the plains, these trade winds bring southwest monsoon.

Bay of Bengal Branch:

• It is sometimes referred to as the South-East Monsoon. This branch of monsoon flows along the Bay of Bengal.
• It moves quickly and arrives in the country’s north-eastern region in the first week of June.
• The heating of the continent creates low pressure, which attracts southeast trade winds from the high-pressure area of the seas.
• Monsoon winds move from a high-pressure area to a low-pressure area. A south-east monsoon from the Bay of Bengal is expected.
• In the Northern Plains, this combines with southwest trade winds.

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What Do You Understand About the Summer Monsoon?

• The summer monsoon is known for its tremendous rains. It usually takes place between the months of April and September.
• These locations experience a humid environment and intense rains during the summer monsoon.
• The summer monsoon is critical to India and Southeast Asia. Agriculture, for example, is reliant on yearly rainfall. For the remainder of the year, the summer monsoon fills wells and aquifers.
• The region’s economy suffers when the summer monsoon is late or poor.
• The summer monsoon has been referred to as India’s genuine finance minister.

What Do You Understand About the Winter Monsoon?

• The winter monsoon in the Indian Ocean, which lasts from October to April, is less well-known than its wet summer counterpart.
• The northeast winds blow during the dry winter monsoon. These winds originate in the atmosphere above Mongolia and northern China.
• Winter monsoons in Southeast Asia are less strong than summer monsoons, in part because the Himalaya Mountains block most of the wind and precipitation from reaching the shore.
• The Himalayas also keep most of the chilly air out of regions like southern India and Sri Lanka, keeping them warm all year.
• Droughts are occasionally accompanied with winter monsoons.

Factors affecting Indian Monsoon In India for UPSC Exam

Coriolis Force:

• The Coriolis Force is a fictitious force that exists only due to the spinning action of the Earth.
• This force is also responsible for the rotational motion observed in tropical cyclones.
• As a result, the monsoon winds are diverted eastwards and now blow from the south-west to the north-east.
• Because the rotating motion of the Earth is constant, the Coriolis Force experienced by a particular parcel of air with a specific velocity at a certain latitude is likewise constant.

Mascarene High:

• The Mascarene High is regarded as the driving force behind the southwest monsoon winds in the Indian subcontinent.
• This high-pressure area often forms by mid-April, and its strength is an essential element in determining the severity of the monsoon in India.
• A stronger high pressure will result in greater winds or a stronger monsoon current.
• If the development of Mascarene High is delayed, it is possible that the onset of monsoon in India may be delayed as well.

Indian Summer:

• Winds move from places of high pressure to areas of low pressure.
• The Himalayan range plays an important role in summer heating by preventing cold air from the north from entering and allowing warmth to occur.
• During this season, the country of India becomes extremely hot. Temperatures in the oceans surrounding the nation are also rising.
• We notice a gradient between air pressure over the sea and that over India as a result of the various heating rates and capacities of air over the sea and that over the land (especially Rajasthan). 
• The air pressure over India is lower than the air pressure over the southern Arabian Sea and the Bay of Bengal. The monsoon winds are drawn in by this method.

Indian Ocean Dipole:

• N H Saji of Japan’s University of Aizu and colleagues found an ENSO-like phenomena in the Indian Ocean in 1999 and dubbed it the Indian Ocean Dipole (IOD).
• IOD, like ENSO, has three phases: positive, negative, and neutral. During the positive phase of IOD, sea surface temperatures in the western Indian Ocean are warmer than those in the eastern Indian Ocean.
• The opposite occurs during the IOD negative phase, and no gradient is noticed during the IOD neutral period.
• It has been found that during the positive IOD phase, the Indian summer monsoon rainfall is significantly higher than during the negative IOD period.

El Nino Southern Oscillation:

• The oscillatory phase of sea surface temperatures around the equatorial Pacific Ocean is referred to as the El Nino Southern Oscillation (ENSO).
• For a long time, forecasters have struggled with ENSO because of its mainly unexpected character.
• Because it impacts air circulation, ENSO has been a driver of worldwide weather (especially in nations bordering the Pacific Ocean).

Intertropical Convergence Zone(ITCZ)

• In equatorial latitudes, the Inter Tropical Convergence Zone (ITCZ) is a large trough of low pressure.
• This is where the trade winds from the northeast and southeast meet.
• This convergence zone is roughly parallel to the equator, although it travels north and south with the apparent movement of the sun.
• The strength and location of this high-pressure system have an impact on the Indian Monsoon.

Tropical Easterly Jet

• The TEJ is critical in kicking off the southwest monsoon.
• This jet falls over the Indian Ocean (around Madagascar) and deepens its high pressure cell, causing a south-west monsoon to form.
• When the summer temperature of the air over Tibet remains high for an extended period of time, it aids in the development of the easterly jet, resulting in heavy rainfall in India.
• If the snow on the Tibet Plateau does not melt, the easterly jet does not form. This has a negative impact on the incidence of rainfall in India.
• As a result, every year with heavy and widespread snow in Tibet will be followed by a year with a weak monsoon and less rainfall.

El Nino

• This is the term used to describe the occasional emergence of a warm ocean current along Peru’s coast as a temporary substitute for the cold Peruvian current.
• ‘El Nino’ is a Spanish term that means ‘the kid,’ and it relates to the infant Christ, as this stream begins to flow during the Christmas season.
• El Nino causes a rise in sea-surface temperatures and a decrease of the trade winds in the region.

What Do You Understand About The Onset of the South-West Monsoon?

• With the apparent movement of the Sun, the position of the ITCZ varies north and south of the equator.
• The sun shines vertically over the Tropic of Cancer in June, while the ITCZ moves northward.
• Under the influence of Coriolis force, the southern hemisphere’s southeast trade winds cross the equator and begin blowing in a southwest to northeast direction.
• As they pass over the warm Indian Ocean, these winds pick up moisture.
• The ITCZ changes to 20°-25° N latitude in July and is positioned in the Indo-Gangetic Plain, while the south-west monsoons blow from the Arabian Sea and the Bay of Bengal. The ITCZ at this position is commonly referred to as the Monsoon Trough.
• The phenomena of the withdrawal of the westerly jet stream from its location over the north Indian plain, south of the Himalayas, is also connected to the shift in the position of the ITCZ.
• The relief and thermal low pressure over northwest India change the direction of these winds as they reach the land.
• The monsoon enters the Indian mainland through two channels: the Arabian Sea Branch and the Bay of Bengal branch.

What Do You Understand About The Retreating Monsoon Season?

• Clear sky and an increase in temperature signal the end of the southwest monsoon season.
• The ground is still wet. The weather becomes unpleasant as a result of the high temperature and humidity. This is usually referred to as the ‘October heat.’
• The temperature begins to drop significantly in the second half of October, particularly in northern India.
• The weather during the receding monsoon is dry in north India, but rainy in the eastern section of the Peninsula.
• The rainiest months in this region are October and November.
• The extensive rain during this season is caused by the passage of cyclonic depressions that start over the Andaman Sea and manage to traverse the southern Peninsula’s eastern coast. These tropical cyclones are extremely dangerous.
• These depressions and cyclones are responsible for the majority of the rainfall on the Coromandel Coast.
• In contrast to the rest of the country, which receives rain during the southwest monsoon season from June to September, the northeast monsoon is critical for agricultural and water security in the south.

Consequences of Monsoons on Life in India

Positive Consequences

• Agriculture provides a living for around 64% of the population in India, and agriculture is dependent on the monsoon.
• India’s agricultural success is heavily reliant on timely and evenly distributed rainfall. Agriculture suffers if it fails, especially in areas where irrigation systems have not been established.
• Regional differences in monsoon climate aid in the cultivation of a variety of crops.
• In India, regional monsoon variance is expressed in a wide range of food, clothing, and housing styles.
• Monsoon rain serves to replenish dams and reservoirs, which are then utilised to generate hydroelectric power.
• Winter rains from temperate cyclones in north India are extremely beneficial to Rabi crops.

Negative Consequences

• Every year, the variability of rainfall causes droughts or floods in various sections of the nation.
• Soil erosion is an issue across huge parts of India as a result of a sudden monsoon burst.
• Sudden rainfall causes landslides in steep locations, causing damage to natural and physical infrastructure and interrupting human life economically and socially.

In this article, we have studied the features associated with the Advancing and Retreating Monsoon in India. Besides, we have understood the significance of this phenomenon for India.

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