The Southwest Monsoon is the rainy season that lasts from June to September. The Southwest Monsoon is the Indian subcontinent's primary rainy season. The southwest monsoon holds over the country during the summer monsoon season. During this time, the country receives nearly 75% of its annual rainfall. This article will explain to you about the Southwest Monsoon Season which will be helpful in preparing Geography for the UPSC Civil service exam.

What is the Southwest Monsoon Season?

• The Southwest Monsoon Season, also called Rainy Season, is from June to September.
• This southwest monsoon is caused by an intense low-pressure system forming over the Tibetan Plateau as a result of intense heating during the summer season.
• They bring a lot of moisture with them as they pass over the equatorial warm currents.
• The rain begins when these winds hit or strike the mountain barriers.
• These southeast trade winds cross the equator and enter the Bay of Bengal and the Arabian Sea, only to become entangled in the air circulation over India.
• They travel in a southwesterly direction after crossing the equator. Southwest monsoons are named after this.
• Most parts of the country experience heavy rainfall due to the monsoon season winds.

Temperature during Southwest Monsoon Season

• The onset of the South West Monsoons causes a significant temperature drop [3° to 6°C].
• During the rainy season, the temperature is less uniform.
• With the end of the southwest monsoons, the temperature rises in September.
• Whenever there is a break in the monsoons, the temperature rises.
• Due to clouds and rain, the diurnal temperature range is small.
• West of the Aravali, the highest temperatures [38° to 40°C] can be found. Due to a lack of clouds and warm continental air masses, this is the case.
• Temperatures in other parts of Northwest India are also above 30°C.
• Due to heavy rainfall, temperatures in the Western Ghats are quite low.
• Temperatures in the coastal areas of Tamil Nadu and adjoining parts of Andhra Pradesh are above 30°C due to the lack of rainfall during this season.

Pressure and Winds During South West Monsoon Season

• Due to the high temperature, low pressure prevails over northwest India.
• The Ganga plain is home to the ITCZ (monsoon trough). Its location is subject to frequent changes depending on the weather.
• The atmospheric pressure continues to rise as it moves southward.
• Winds from the Arabian Sea and the Bay of Bengal blow southwest to northeast over the peninsular region due to a pressure gradient between north and south.
• In the Indo-Gangetic plain, where they move from east to west, their direction changes.

Rainfall During South West Monsoon Season

• This season receives three-quarters of the total annual rainfall.
• This season, the average rainfall across India's plains is around 87 percent.
• In the Andaman and Nicobar Islands, the monsoon usually arrives on the 20th of May.
• The monsoon moves much faster in the Bay of Bengal than it does in the Arabian Sea.
• The onset of the southwest monsoon over Kerala, i.e. the first point of entry into India's mainland, is usually on June 1st.
• The monsoons arrive quickly, bringing with them a lot of thunder, lightning, and heavy rain. Monsoon burst is the name given to this sudden onset of rain.
• Monsoons can be delayed or arrive much earlier than expected.
• The onset usually occurs between the 29th of May and the 7th of June.
• The earliest onset dates were May 11th, 1918, and May 11th, 1955, respectively, while the most delayed onset date was June 18th, 1972.

Branches of South West Monsoon

• Beyond south Kerala, monsoon winds split into two branches:
  • The Arabian Sea branch
  • The Bay of Bengal branch
• The Arabian Sea branch moves northwards gradually. By the 10th of June, it will have arrived in Mumbai.
• The Bay of Bengal branch quickly spreads across most of Assam. It is expected to arrive in Kolkata on June 7th.
• The Bay branch is deflected westward by the Himalayan barrier as it approaches the Himalayan foothills, and it advances up the Gangetic plain.
• The two branches come together to form a single current mostly around Delhi.
• Both branches arrive in Delhi at roughly the same time.
• West Uttar Pradesh, Haryana, Punjab, Rajasthan, and finally Himachal Pradesh and Kashmir are all affected by the combined current.
• The monsoon is usually established over most of the country by the end of June.
• By mid-July, the monsoon has spread throughout Kashmir and the rest of the country.
• It will lose most of its moisture by the time it reaches Kashmir.
• For the following reasons, the Arabian Sea branch of the monsoon is much stronger than the Bay of Bengal branch:
  • The Arabian Sea is larger than the Bay of Bengal.
  • The entire Arabian Sea current advances towards India, whereas only a portion of the Bay of Bengal current enters India, with the remainder flowing to Myanmar, Thailand, and Malaysia.

Streams of Arabian Sea Branch

When the Arabian Sea branch of the southwest monsoons reaches India's mainland, it splits into three distinct streams.

• The first stream hits India's west coast, dumping over 250 cm of rain on the country.
• It strikes the Western Ghats perpendicularly, resulting in abundant Orographic Rainfall [400 to 500 cm annual rainfall on the windward side].
• On the leeward side of the crest, rainfall is reduced to about 30-50 cm.
• On the immediate leeward side of the Western Ghats, there is a narrow belt of severe aridity.
• However, once it has passed, the air begins to rise again, and rainfall amounts increase further east.
• The second stream flows through the Narmada—Tapi troughs (narrow rift valley) before reaching central India.
• Due to the lack of a major orographic obstacle across the rift, it does not produce much rain near the coast.
• This stream brings rain to some parts of central India (Ex: Nagpur).
• The third stream runs parallel to the Aravali Range and does not produce much rain. As a result, Rajasthan is primarily a desert state.
• On the south-eastern edge of the Aravali Range, however, there is some orographic effect.
• Mt. Abu receives about 170 cm of rain, whereas the surrounding plains receive only 60 to 80 cm.

Streams of Bay of Bengal Branch

The southwest monsoon's Bay of Bengal Branch is divided into two distinct streams.

• The first stream reaches Meghalaya after crossing the Ganga-Brahmaputra delta.
• The orographic effect causes heavy rainfall in this area. Cherrapunji receives 1,102 cm of annual rainfall, the majority of which falls between June and August.
• Mawsynram (the current champion), which is located at 1,329 meters above sea level and is only 16 kilometers west of Cherrapunji (the X champion), receives more annual rainfall (1,221 cm).
• Both stations are at the northern end of a deep valley that runs from south to north on the southern slopes of the Khasi hills.
• The Bay of Bengal branch's second stream flows along the Himalayan foothills, deflected to the west by the Himalayas, bringing widespread rainfall to the Ganga plain.
• As we move from east to west up the plain, the rainfall from this stream decreases steadily.
• The rain shadow effect of the Arabian Sea current and the Bay of Bengal current, which flow parallel to the coast, keeps the Tamil Nadu coast relatively dry during the southwest monsoon season.

Break in the South West Monsoons

• During the Monsoon season, the Monsoon trough shifts to the Himalayan foothills, resulting in a sharp decrease in rainfall in most parts of the country but an increase in the Himalayas, Northeast India, and the Southern Peninsula.
• There are times in July and August when the monsoons are particularly weak.
• Outside of the Himalayan belt and the southeast peninsula, rainfall is practically non-existent. This is referred to as a monsoon break.
• Breaks are most likely to take place during the second week of August and will last a week.
• The breaks are thought to have been caused by the monsoon trough shifting northward (minimum low-pressure cell in ITCZ).
• During the break period, the axis of the trough is located in the Himalayan foothills.
• The monsoon trough is a part of the Intertropical Convergence Zone, which can be seen as a line on a weather map showing the locations of minimum sea level pressure, and is a zone where the wind patterns of the southern and northern hemispheres converge.
• During the break, heavy rainfall occurs in the sub-Himalayan regions and on the Himalayan southern slopes.
• During the rainy season, there are usually one or two breaks. There is a break in the monsoons 85 times out of 100 years.

Depressions in South West Monsoon Season

• Depressions [intense low pressure] originating in the Arabian Sea and Bay of Bengal are responsible for a large portion of the rainfall in the South West Monsoon.
• Some depressions form over land as well.
• From June to September, about 3-4 depressions form per month.
• Almost all of them are trapped inward through the deltas of great rivers like the Ganga, Mahanadi, Godavari, Krishna, and Cauvery [they need moisture to survive] and cause heavy rain in these areas.
• The latitudinal position of ITCZ is strongly correlated with the location of depressions.
• The majority of the depressions in the Bay of Bengal originate west of 900 E and move north-west.
• In June-July, depressions in the Arabian Sea move northwest or northerly, potentially affecting west Gujarat or Maharashtra.
• Storms are relatively rare in August and September, and they form near the Maharashtra-Gujarat coast.
• These depressions are responsible for the majority of the rainfall in the country's central and northern regions.
• Deficits or no rain result from the absence of depression or a change in their tracks.

Factors Influencing South-West Monsoon Formation

Differential Heating and Cooling of Land and Water

• Due to the differential heating and cooling of land and water, India's landmass has low pressure, while the seas around it have relatively high pressure.
• This greatly impacts the formation of South-West Monsoons.
• As a result of this, the direction of monsoon winds is reversed.

InterTropical Convergence Zone (ITCZ)

• During the summer months, the ITCZ swings north, bringing monsoon rains to Kozhikode, India.
• During the summer in the Southern Hemisphere, the ITCZ drops south, bringing monsoon rains to Darwin, Australia.
• The fact that land cannot hold heat, as well as the ocean, has an impact on the location of monsoon rainfall.

Presence of the High-Pressure Area

• The presence of a high-pressure area over the Indian Ocean, east of Madagascar, at about 20°S.
• The Indian Monsoon is affected by the intensity and location of this high-pressure area.
• During the summer, the Tibetan plateau becomes extremely hot, resulting in strong vertical air currents and the formation of low pressure over the plateau at about 9 kilometers above sea level.

Tropical Easterly Jet (African Easterly Jet)

• Tropical depressions are directed into India by the easterly jet stream.
• The distribution of monsoon rainfall over the Indian subcontinent is influenced by these depressions.
• The areas of India with the most rainfall are along the tracks of these depressions.

Southern Oscillation (SO)

• The Southern Oscillation (SO) occurs when the tropical eastern south Pacific Ocean has high pressure while the tropical eastern Indian Ocean has low pressure.
• However, there is a reversal in pressure conditions every few years, with the eastern Pacific having lower pressure than the eastern Indian Ocean.
• The SO is a term that refers to a periodic change in pressure conditions.
• As those conditions change, summer temperatures in parts of India can reach 45 degrees Celsius, while the Indian Ocean is significantly cooler.
• Weaker monsoons and even droughts are also sometimes the result of the above conditions.

Climate Change

• As the atmosphere warms as a result of climate change, it can hold more water vapor, which affects how our monsoon behaves.
• According to new research, global warming is likely to make India's monsoon season wetter and more dangerous.
• Climate change has been disrupting the monsoon season for years, according to scientists.
• Previous research has suggested that increased moisture in the warmed atmosphere, as a result of global warming caused by greenhouse gases, will result in rainier summer monsoon seasons and unpredictable, extreme rainfall events.

Significance of Southwest Monsoon Season

• Over half of India's farmland is irrigated by the southwest monsoon.
• During the monsoon season, India receives roughly 70% of its annual rainfall, which has an impact on the yield of some key kharif or summer crops like rice, pulses, and oilseeds like soybeans.
• Cotton, maize, paddy, soybean, groundnut, bajra, and sesame are some of the most important crops that rely on Monsoon rains.
• In India, dairy farms rely on the Southwest Monsoon to keep their cows healthy and well-fed.

Conclusion

By the beginning of September, Southwest Monsoon starts retrieving from the far northwest and gradually moves southward. However, heavy rains brought on by these monsoon winds can cause devastating floods in India's Northern Plains, causing loss of life and property. They are notorious for their unpredictability. Droughts and heavy floods are caused by dry and wet spells in one part of the country, while droughts are possible in the other.

FAQs

Question: What is the Southwest Monsoon?

Question: What are the two branches of the Southwest Monsoon?

Question: How does the Southwest Monsoon affect Indian agriculture?

Question: What causes the onset of the Southwest Monsoon?

Question: Which regions in India receive the maximum rainfall during the Southwest Monsoon?

MCQs

1. What is the main cause of the Southwest Monsoon in India?

a) Earth's axial tilt

b) Differential heating of land and water

c) Ocean currents

d) Winds from the Arctic

2. Which branch of the Southwest Monsoon is responsible for rainfall in Kerala?

a) Arabian Sea branch

b) Bay of Bengal branch

c) Pacific Ocean branch

d) Indian Ocean branch

3. Which crop depends heavily on the Southwest Monsoon in India?

a) Wheat

b) Rice

c) Barley

d) Millets

4. Which region in India receives the highest rainfall during the Southwest Monsoon?

a) Rajasthan

b) Punjab

c) Western Ghats

d) Gujarat

5. Which of the following locations is known as the wettest place on Earth during the Southwest Monsoon?

a) Ladakh

b) Mawsynram

c) Jaisalmer

d) Kanyakumari

GS Mains Questions and Model Answers

Q1: Discuss the factors influencing the onset and intensity of the Southwest Monsoon in India.

Answer: Several factors influence the onset and intensity of the Southwest Monsoon, including the differential heating of land and water, the presence of the Inter-Tropical Convergence Zone (ITCZ), the strength of the Mascarene High, and the impact of El Niño and La Niña phenomena. The monsoon is also affected by the Himalayan mountain range, which acts as a barrier, forcing the winds to rise and condense, resulting in rainfall. The Southern Oscillation also plays a critical role in determining the monsoon's strength and distribution.

Q2: Analyze the socio-economic impact of the Southwest Monsoon on India.

Answer: The Southwest Monsoon is the lifeline of India’s agricultural sector, providing vital water for irrigation. A good monsoon season boosts crop production, enhances rural incomes, and promotes overall economic growth. However, a delayed or deficient monsoon can lead to droughts, reduced agricultural yields, water scarcity, and inflation in food prices. Industries like hydropower, fisheries, and tourism are also significantly influenced by the monsoon. Thus, the monsoon has a direct impact on employment, food security, and rural livelihoods in India.

Q3: Examine the regional variations in the distribution of monsoon rainfall across India.

Answer: Monsoon rainfall varies greatly across India due to factors like topography and proximity to the coast. The Western Ghats and northeastern regions receive heavy rainfall due to the orographic effect. In contrast, the interior Deccan plateau and parts of Rajasthan receive much less rainfall. The Bay of Bengal branch brings substantial rainfall to the northeastern states, while the Arabian Sea branch affects western India. Rain-shadow regions like Tamil Nadu remain relatively dry during the Southwest Monsoon, receiving rainfall during the Northeast Monsoon.

Previous Year Questions on Southwest Monsoon Season

1. UPSC CSE Prelims 2017:

Question: The main source of rainfall during the Southwest Monsoon in India is:

A. Cyclones

B. Western Disturbances

C. Moisture-laden winds from the Indian Ocean

D. Local convectional rainfall

Answer: C

Explanation: The Southwest Monsoon is primarily driven by moisture-laden winds from the Indian Ocean, which bring heavy rainfall across India between June and September.

2. UPSC CSE Mains 2016 (GS Paper 1):

Question: Discuss the role of the Southwest Monsoon in shaping the socio-economic life of India.

Answer: The Southwest Monsoon plays a critical role in India’s economy, especially in the agricultural sector. Nearly 60% of Indian agriculture is rain-fed, making monsoon rainfall crucial for Kharif crops like rice, sugarcane, and cotton. The monsoon also impacts hydroelectric power generation and water availability for drinking and irrigation. Moreover, timely and adequate monsoon rainfall can prevent droughts, ensuring food security and stabilizing the economy. Conversely, erratic or deficient monsoons can lead to agricultural losses and water scarcity, impacting millions of livelihoods.

3. UPSC CSE Prelims 2018:

Question: Which region in India is first to receive the onset of the Southwest Monsoon?

A. Western Rajasthan

B. Kerala

C. Tamil Nadu

D. Gujarat

Answer: B 

Explanation: The onset of the Southwest Monsoon occurs in Kerala, usually by the first week of June, marking the beginning of the monsoon season in India.