Arrange the following States cn the basis of ascending dates of the onset of monsoon : 1. Uttar Pradesh 2. West Bengal 3. Kerala 4. Rajasthan Select the correct answer using the code given below : Code :

1. Mechanism of the Southwest Monsoon (basic)

To understand the Southwest Monsoon, we must first look at it not just as 'rain,' but as a massive, seasonal reversal of wind patterns. Historically, this was explained through the Thermal Concept proposed by Edmund Halley in 1686. He suggested that during summer, the huge landmass of Asia heats up much faster than the surrounding oceans. This creates a strong low-pressure centre over North-West India and Pakistan, while the cooler oceans maintain high pressure. Air naturally flows from high to low pressure, driving moisture-laden winds toward the Indian subcontinent Geography of India (Majid Husain), Chapter 4: Climate of India, p.1.

However, modern meteorology provides a more complete picture through the Dynamic Concept. This focuses on the Inter-Tropical Convergence Zone (ITCZ)—a low-pressure belt where trade winds from the Northern and Southern Hemispheres meet. As the sun moves north toward the Tropic of Cancer in summer, the ITCZ also shifts northward, eventually positioning itself over the Gangetic Plain (around 20°N-25°N). When the Southeast Trade Winds from the Southern Hemisphere cross the equator to reach this low-pressure zone, they are deflected to the right by the Coriolis Force. These winds then enter India from the southwest, giving the season its name: the Southwest Monsoon INDIA PHYSICAL ENVIRONMENT (NCERT 2025 ed.), Chapter 4: Climate, p.30.

The arrival of these winds is not simultaneous across the country but follows a distinct geographical sequence. The monsoon typically 'bursts' on the Malabar Coast (Kerala) by June 1. It then splits into two branches—the Arabian Sea branch and the Bay of Bengal branch. The Bay of Bengal branch moves rapidly up the coast, reaching West Bengal by early June, then advances through the Gangetic plains to reach Uttar Pradesh by mid-June. Finally, the winds reach the arid regions of Rajasthan by early July, making the Thar Desert the last region to witness the onset INDIA PHYSICAL ENVIRONMENT (NCERT 2025 ed.), Chapter 4: Climate, p.35.

Region	Typical Onset Date
Kerala (Malabar Coast)	June 1
West Bengal (Kolkata)	June 5 - June 10
Uttar Pradesh	June 15 - June 20
Rajasthan (Thar Desert)	Early to Mid-July

Sources: Geography of India (Majid Husain), Chapter 4: Climate of India, p.1-3; INDIA PHYSICAL ENVIRONMENT (NCERT 2025 ed.), Chapter 4: Climate, p.30-35

2. The Two Branches: Arabian Sea and Bay of Bengal (basic)

As the moisture-laden Southwest Monsoon approaches the Indian landmass, it encounters the tapering shape of the Indian peninsula. This geographic feature acts like a wedge, bifurcating the single monsoon stream into two distinct branches: the Arabian Sea Branch and the Bay of Bengal Branch. This split is a defining moment in the Indian climatic calendar, determining which regions get rain and when Majid Husain, Climate of India, p.16.

The Arabian Sea Branch is considerably more powerful—roughly three times stronger than its eastern counterpart. It advances in three main streams:

• The first strikes the Western Ghats, causing heavy orographic rainfall on the windward side.
• The second enters through the Narmada and Tapi river valleys, carrying moisture into Central India and reaching the Chotanagpur plateau NCERT Class XI, Climate, p.35.
• The third strikes the Saurashtra and Kachchh regions, passing over Rajasthan toward the Himalayas.

Parallelly, the Bay of Bengal Branch moves northwards. Interestingly, it doesn't just travel straight up; it strikes the Arakan Coast of Myanmar and the hills of Southeast Bangladesh. The Arakan Hills and the mighty Himalayas act as a barrier, deflecting this branch westward. Consequently, instead of moving south-to-north, the monsoon enters West Bengal and the Ganga Plains from the southeast and south, moving toward the Punjab plains NCERT Class XI, Climate, p.37. Another part of this branch is funneled into the Brahmaputra valley, leading to world-record rainfall in places like Mawsynram on the Meghalaya Plateau Majid Husain, Climate of India, p.16.

Feature	Arabian Sea Branch	Bay of Bengal Branch
Entry Point	Western Coast (Kerala/Mumbai)	Eastern Coast (West Bengal/Bangladesh)
Key Barrier	Western Ghats	Arakan Hills & Himalayas
Movement	Northward & Eastward	Westward (along Ganga Plains) & Northeastward

Sources: Geography of India, Majid Husain, Climate of India, p.16; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.35-37

3. Global Drivers: ENSO and Jet Streams (intermediate)

To understand why the Indian monsoon varies from year to year, we must look far beyond India's borders to the Pacific and Indian Oceans. The most significant global driver is the ENSO (El Niño-Southern Oscillation). In a "normal" year, strong trade winds push warm surface waters toward Asia, creating a low-pressure zone over the Western Pacific that acts as a vacuum, pulling moisture toward the Indian subcontinent. However, during an El Niño event, these trade winds weaken, and the warm water shifts eastward toward South America. This disrupts the Walker Circulation, often leading to weaker monsoon rains or even droughts in India Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415. Conversely, La Niña—the cooling of the central Pacific—typically enhances the Indian monsoon, bringing surplus rainfall.

Closer to home, the Indian Ocean Dipole (IOD) acts as the "Pacific's sibling" in the Indian Ocean. It is a seesaw of sea-surface temperatures between the western pole (Arabian Sea) and the eastern pole (near Indonesia). A Positive IOD occurs when the western Indian Ocean becomes unusually warm. This setup is a boon for India because it intensifies the moisture-laden winds heading toward the coast. Remarkably, a strong Positive IOD can sometimes "save" the monsoon even during an El Niño year, as seen in 1997 Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.416.

Phenomenon	Condition for Strong Monsoon	Condition for Weak Monsoon
ENSO	La Niña (Cold Eastern Pacific)	El Niño (Warm Eastern Pacific)
IOD	Positive (Warm Western Indian Ocean)	Negative (Warm Eastern Indian Ocean)

Finally, the Jet Streams act as the atmospheric "gatekeepers." For the southwest monsoon to establish itself, the Sub-Tropical Westerly Jet (STWJ), which flows over the Himalayas during winter, must retreat northward into Central Asia. This vacancy allows the Tropical Easterly Jet (TEJ) to form over the peninsula. The TEJ is a high-altitude wind that creates a massive "pumping" effect, sucking air from the surface and forcing the moisture-heavy southwest winds to rush into the Indian landmass Physical Geography by PMF IAS, Earths Atmosphere, p.274.

Sources: Physical Geography by PMF IAS, El Nino, La Nina & El Nino Modoki, p.415-416; Physical Geography by PMF IAS, Earths Atmosphere, p.274

4. Withdrawal of Monsoon and North-East Monsoon (intermediate)

The Withdrawal of the Monsoon (also known as the Retreating Monsoon) is a gradual process that marks the transition from the wet rainy season to the dry winter season. Unlike the sudden 'burst' of the onset, the retreat is steady and occurs as the sun begins its southward migration, weakening the low-pressure system over the Indian subcontinent Geography of India, Majid Husain, Climate of India, p.25. The withdrawal begins in Northwest India (specifically the Punjab and Rajasthan plains) by the third week of September. This is logically consistent: the regions that receive the monsoon last are often the first to see it leave Certificate Physical and Human Geography, GC Leong, The Tropical Monsoon and Tropical Marine Climate, p.159. By mid-October, the southerly branch of the jet stream returns to its winter position south of the Himalayas, signaling the definitive end of the summer monsoon across northern India.

During this transition (October and November), a unique phenomenon known as 'October Heat' occurs. As the monsoon clouds clear, the sun shines brightly on the still-saturated, moist land. This combination of high temperature and high humidity creates oppressive, sultry weather conditions INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.37. While North India becomes dry and starts cooling rapidly by late October, the retreating winds shift their focus to the Peninsula. These winds, now blowing from the northeast, are generally dry as they originate over land. However, as they cross the Bay of Bengal, they pick up significant moisture Physical Geography by PMF IAS, Climatic Regions, p.431.

This moisture-laden North-East Monsoon is the primary source of rainfall for the southeastern coast of India. Between October and December, it brings torrential rain to Tamil Nadu, southern Andhra Pradesh, and parts of Kerala and Karnataka INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.34. While the rest of the country prepares for a dry winter, the Coromandel Coast experiences its rainiest months. It is important to distinguish this from the winter rains in Northwest India (Punjab), which are caused by Western Disturbances (temperate cyclones) rather than the North-East Monsoon winds themselves Physical Geography by PMF IAS, Climatic Regions, p.431.

Feature	South-West Monsoon (Onset)	Retreating/North-East Monsoon
Nature	Sudden 'Burst'	Gradual and steady withdrawal
Wind Direction	Sea to Land (South-West)	Land to Sea (North-East)
First to Experience	Kerala (Malabar Coast)	North-West India (Punjab/Rajasthan)
Major Rainfall Area	Most of India	Tamil Nadu and South-East Peninsula

Sources: Geography of India, Majid Husain, Climate of India, p.25; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.34-37; Certificate Physical and Human Geography, GC Leong, The Tropical Monsoon and Tropical Marine Climate, p.159; Physical Geography by PMF IAS, Climatic Regions, p.431

5. Western Disturbances and Winter Precipitation (intermediate)

While the Southwest Monsoon dominates India's summer, the winter weather in Northern India is shaped by a distinct phenomenon known as Western Disturbances (WDs). These are extra-tropical cyclones—low-pressure systems that originate far away over the Mediterranean Sea. They travel thousands of kilometers across Turkey, Iraq, Iran, and Pakistan before entering the Indian subcontinent from the northwest Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.52. These systems are not driven by surface trade winds but are carried into India by the Subtropical Westerly Jet Stream, a high-altitude wind current Physical Geography by PMF IAS, Temperate Cyclones, p.410.

The impact of Western Disturbances is most significant between November and May, peaking during the winter months of December to April. Although the total volume of rainfall they bring is "meagre" compared to the summer monsoon, its economic and ecological value is immense. In the plains of Punjab, Haryana, and Western Uttar Pradesh, the light rain is a lifeline for Rabi crops, particularly wheat INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.33. In the Himalayan region, this precipitation takes the form of snowfall, which is crucial because it feeds the glaciers that sustain the flow of perennial rivers during the scorching summer months.

Feature	Western Disturbances	Southwest Monsoon
Origin	Mediterranean Sea (Temperate/Extra-tropical)	Indian Ocean (Tropical)
Carrier	Westerly Jet Streams	Low-level Trade Winds
Direction of Travel	West to East	South to North / West to East
Rainfall Gradient	Decreases from West to East	Decreases from East to West (in North India)

One characteristic feature of WDs is their spatial distribution: the precipitation goes on decreasing from west to east in the plains. For instance, Punjab receives more winter rain than Bihar INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.33. Furthermore, the arrival of these disturbances is often followed by cold waves, where clear skies and the influx of cold air from the north cause temperatures to plummet across northern and central India Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.52.

Sources: Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.52; Physical Geography by PMF IAS, Temperate Cyclones, p.410; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.33

6. Spatio-Temporal Progress of Monsoon Onset (exam-level)

The arrival of the Southwest Monsoon in India is not a single event but a gradual, albeit dramatic, progression known as the "burst." This journey begins when the heating of the Indian landmass causes the Inter-Tropical Convergence Zone (ITCZ) to shift northward, reaching approximately 25°N by July. This shift creates a powerful low-pressure trough that draws in moisture-laden winds from the Indian Ocean INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.34. While the monsoon actually reaches the Andaman and Nicobar Islands and Sri Lanka by the last week of May, its official "burst" on the Indian mainland occurs at the Malabar Coast in Kerala around June 1 Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 4: Climate of India, p.16.

Upon hitting the tapering southern peninsula, the monsoon current bifurcates into two distinct branches: the Arabian Sea Branch and the Bay of Bengal Branch. The Arabian Sea branch moves northward along the Western Ghats, reaching Mumbai by June 10. Simultaneously, the Bay of Bengal branch advances rapidly through the Bay, striking the coast of West Bengal and Bangladesh. Due to the presence of the Himalayas and the orientation of the monsoon trough, this branch is deflected westward, reaching Kolkata by June 7 and moving up the Gangetic Plain Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 4: Climate of India, p.17.

As these two branches advance, they eventually merge over the northern plains. The monsoon reaches Uttar Pradesh by mid-June (roughly June 15–20) and continues its northwestward trek. By the first week of July, the monsoon is established over most of India. The very last region to receive the monsoon is the Thar Desert in Rajasthan, typically by mid-July. By the time it reaches this far west, the winds have often shed most of their moisture, resulting in the desert's characteristic aridity Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 4: Climate of India, p.17.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.34; Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 4: Climate of India, p.16; Geography of India, Majid Husain (McGrawHill 9th ed.), Chapter 4: Climate of India, p.17

7. Solving the Original PYQ (exam-level)

This question perfectly synthesizes your understanding of the spatial progression of the Southwest Monsoon. Having studied the "burst" mechanism and the bifurcation into two branches, you can now apply the logic of geographical proximity and pathing. The monsoon typically arrives at the Malabar Coast in Kerala by June 1st, marking the primary entry point for the Arabian Sea branch. Almost simultaneously, the Bay of Bengal branch advances rapidly toward the northeast and the eastern coast, reaching West Bengal shortly after (around June 5-10). As these moisture-laden winds move inland up the Indo-Gangetic Plain from east to west, they arrive in Uttar Pradesh by mid-June, finally reaching the far-western regions of Rajasthan last, often by early July. As detailed in INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), this predictable march allows us to establish the correct sequence as 3-2-1-4.

When evaluating the options, the most common trap is misjudging the east-to-west movement across Northern India or the timing of the two branches. Option (C) incorrectly places Uttar Pradesh before West Bengal, ignoring that the monsoon must pass through the deltaic regions before reaching the central plains. Similarly, Option (A) suggests West Bengal precedes Kerala; however, while the Bay of Bengal branch is fast, the formal onset of the Indian monsoon is traditionally marked by the Kerala burst. UPSC often tests your ability to visualize the isochrones of monsoon arrival, where the distance from the sea and the orientation of the moisture-laden winds dictate the timing. Therefore, (B) 3 - 2-1-4 is the only logical choice that reflects the ascending chronological order of these states relative to the monsoon's path.