Which one of the following sets of states does not receive most of its rainfall from SW monsoon during the months of June to September?

1. Mechanism of the Indian Monsoon (basic)

To understand the Indian Monsoon, we must first look at it through two lenses: the Classical Thermal Theory and the Modern Dynamic Theory. Historically, in 1686, Edmund Halley proposed that the monsoon is essentially a giant, seasonal version of a land and sea breeze. During summer, the massive landmass of Asia heats up much faster than the surrounding oceans, creating a deep thermal low pressure over North-West India and Central Asia Geography of India, Climate of India, p.1. This pressure difference draws moisture-laden winds from the high-pressure zones over the cooler oceans toward the land. However, modern research shows that heat alone isn't the whole story; if it were, the rains would start in April when temperatures first soar, rather than waiting until June Geography of India, Climate of India, p.3.

The modern understanding centers on the Inter Tropical Convergence Zone (ITCZ)—a low-pressure belt near the equator where trade winds from both hemispheres meet. In summer, as the sun moves north toward the Tropic of Cancer, the ITCZ also shifts northward, positioning itself over the Indo-Gangetic plain (around 20°N-25°N). This shift creates what we call the monsoon trough INDIA PHYSICAL ENVIRONMENT, Chapter 4: Climate, p.30. This trough is so powerful that it pulls the Southeast Trade Winds from the Southern Hemisphere across the equator.

As these winds cross the equator, they are influenced by the Coriolis Force, which deflects moving objects to the right in the Northern Hemisphere. Consequently, the winds turn and approach the Indian landmass from a Southwesterly direction, giving the Southwest Monsoon its name. The final piece of the puzzle involves the upper atmosphere: the Westerly Jet Stream must retreat north of the Himalayas, allowing the Tropical Easterly Jet Stream to establish itself over the peninsula, which triggers the sudden 'burst' of the monsoon INDIA PHYSICAL ENVIRONMENT, Chapter 4: Climate, p.31.

Comparison: Classical vs. Modern View

Feature	Classical (Thermal) Theory	Modern (Dynamic) Theory
Primary Driver	Differential heating of land and sea.	Shift of the ITCZ and Jet Streams.
Mechanism	Giant land/sea breeze effect.	Equatorial winds crossing the equator + Coriolis effect.
Scope	Surface level temperature/pressure.	Includes upper-air circulation (Jet Streams).

Sources: Geography of India, Climate of India, p.1-3; INDIA PHYSICAL ENVIRONMENT, Chapter 4: Climate, p.30-31

2. Branches of the Southwest (SW) Monsoon (basic)

To understand the Indian Monsoon, we must first look at the map of India. As the Southwest Monsoon winds approach the landmass, the tapering shape of the Indian Peninsula acts like a wedge, splitting the moisture-laden winds into two distinct streams: the Arabian Sea Branch and the Bay of Bengal Branch Geography of India by Majid Husain, Climate of India, p.16. While both originate from the same parent system, they follow very different paths and interact with India's topography in unique ways.

The Arabian Sea Branch is the more powerful of the two. It strikes the Western Ghats first, causing heavy orographic rainfall on the windward side. It then advances northwards, reaching Mumbai by June 10th and eventually spreading into Central India Geography of India by Majid Husain, Climate of India, p.16. In contrast, the Bay of Bengal Branch behaves quite differently. Instead of heading straight north, it strikes the coast of Myanmar. Here, the Arakan Hills act as a physical barrier, deflecting the winds toward the Indian subcontinent. This is why the monsoon enters West Bengal and Bangladesh from the south and southeast rather than the southwest India Physical Environment (NCERT), Climate, p.37.

Once inside the Indian mainland, the Bay of Bengal branch splits again. One part moves up the Brahmaputra valley, while the other moves westward along the Ganga plains. Eventually, both the Arabian Sea and Bay of Bengal branches merge in the Gangetic Plain of North India. By the time these winds reach the far northwest, like the Thar Desert, they have shed most of their moisture, which is why Rajasthan remains relatively arid even during the peak season Geography of India by Majid Husain, Climate of India, p.17.

Feature	Arabian Sea Branch	Bay of Bengal Branch
Size & Volumne	Larger surface area; carries more moisture.	Smaller area; highly influenced by river runoff.
Primary Barrier	Western Ghats	Arakan Hills (Myanmar) and Himalayas
Salinity	Higher (greater evaporation).	Lower (receives fresh water from Ganga/Brahmaputra) Physical Geography by PMF IAS, Tropical Cyclones, p.358.

Sources: Geography of India by Majid Husain, Climate of India, p.16; Geography of India by Majid Husain, Climate of India, p.17; India Physical Environment (NCERT), Climate, p.37; Physical Geography by PMF IAS, Tropical Cyclones, p.358

3. Orographic Rainfall and the Rain-Shadow Effect (intermediate)

To understand the Indian monsoon, one must first grasp the concept of Orographic Rainfall (from the Greek word oros, meaning mountain). This occurs when moisture-laden winds are physically forced to rise by a relief feature, such as a mountain range. As the air climbs, it undergoes adiabatic cooling—the temperature drops as pressure decreases at higher altitudes. Eventually, the air reaches its dew point, water vapor condenses into clouds, and heavy precipitation is released on the windward side (the slope facing the wind). In India, the Western Ghats (Sahyadris) act as a massive wall, forcing the Arabian Sea branch of the monsoon to rise between 900m and 1200m, resulting in torrential rains of 250 cm to 400 cm on the coastal plains INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4, p.35.

The story changes dramatically once the winds cross the mountain crest. As the air descends the leeward side, it undergoes adiabatic warming due to increasing atmospheric pressure. This warming increases the air's capacity to hold moisture, causing its relative humidity to drop. These descending, or katabatic, winds become dry and stable, leaving the region behind the mountains with significantly less rainfall Physical Geography by PMF IAS, Hydrological Cycle, p.339. This dry zone is known as the Rain-Shadow Area.

Feature	Windward Side (e.g., Mahabaleshwar)	Leeward Side (e.g., Pune)
Air Movement	Ascending and cooling	Descending and warming
Relative Humidity	Increases (leading to saturation)	Decreases (becoming dry)
Rainfall amount	Very High (>600 cm in some areas)	Low (~70 cm)

In the Indian context, this effect explains why the interior parts of Maharashtra, Karnataka, Telangana, and Andhra Pradesh receive much less rainfall compared to the Konkan coast Geography of India by Majid Husain, Climate of India, p.37. Even though these regions are geographically close to the sea-facing coast, the Western Ghats act as a barrier that "shadows" them from the bulk of the monsoon's moisture.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.35; Physical Geography by PMF IAS, Hydrological Cycle (Water Cycle), p.339; Geography of India by Majid Husain, Climate of India, p.37

4. The Retreating Monsoon and Northeast (NE) Monsoon (intermediate)

Once the summer sun begins its 'southward march' toward the Equator, the intense heat over the Indian landmass starts to fade. This triggers a massive atmospheric shift: the Inter Tropical Convergence Zone (ITCZ), which had been sitting over the Ganga plains, begins to move south. As the low-pressure trough weakens and shifts toward the Bay of Bengal, the moisture-laden Southwest winds lose their grip. This transition period, occurring during October and November, is what we call the Retreating Monsoon INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.37. During this time, the weather is characterized by clear skies and a rise in temperature, creating a sticky, oppressive condition known as 'October Heat.'

As the monsoon 'retreats' from Northwest India starting in early September, the wind direction eventually reverses. By winter, the winds blow from the land toward the sea, becoming the Northeast (NE) Monsoon Exploring Society: India and Beyond, Social Science-Class VII, Climates of India, p.55. Because these winds originate over the dry landmass of Central Asia and Tibet, they are generally dry and bring little to no rain to most of India. However, there is a very famous exception: as these winds sweep over the Bay of Bengal, they pick up significant moisture. When they strike the Coromandel Coast, they bring torrential rainfall to Tamil Nadu, southern Andhra Pradesh, and parts of Karnataka and Kerala INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Chapter 4, p.34.

It is important to distinguish this from the rainfall in North India during the same period. While the Southeast coast is getting drenched by the NE Monsoon, the Northwestern parts of India (like Jammu & Kashmir and Punjab) receive winter precipitation from Western Disturbances—temperate cyclones originating far away in the Mediterranean region. Thus, while the rest of the country remains largely dry, these two pockets (the SE Coast and the Northern mountains) have their own unique winter rain schedules.

Feature	Southwest (SW) Monsoon	Northeast (NE) Monsoon
Season	June to September	October to December
Wind Direction	Sea to Land	Land to Sea
Major Beneficiary	Most of India (except TN)	Tamil Nadu & SE Coast

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.37; Exploring Society: India and Beyond, Social Science-Class VII (NCERT Revised ed 2025), Climates of India, p.55; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.34

5. Western Disturbances and Winter Precipitation (intermediate)

While the Southwest Monsoon is the primary source of water for most of India, the winter season brings a unique weather phenomenon known as Western Disturbances (WDs). These are extra-tropical cyclones or low-pressure systems that originate far away over the Mediterranean Sea. As the sun moves southward in winter, the global wind belts shift, allowing the Subtropical Westerly Jet Stream to position itself over the Indo-Gangetic plains. This high-altitude wind acts like a conveyor belt, carrying these moisture-laden disturbances across Turkey, Iran, Afghanistan, and Pakistan before they enter Northwest India Majid Hussain, Environment and Ecology, Natural Hazards and Disaster Management, p.52.

The impact of Western Disturbances is most pronounced between December and April. Unlike the sudden, heavy downpours of the summer monsoon, WDs typically bring light to moderate rainfall in the plains (Punjab, Haryana, and Delhi) and heavy snowfall in the Himalayan regions like Jammu & Kashmir and Himachal Pradesh. This is why J&K is a notable exception to the general rule of Indian rainfall; while the rest of the country dries up after September, J&K receives significant precipitation during the winter months NCERT Class XI, India Physical Environment, Chapter 4, p.34. This winter rain is locally known as Mahawat and is incredibly precious for the Rabi crops, particularly wheat, as it provides much-needed moisture during the grain-filling stage.

Beyond rainfall, Western Disturbances also influence the temperature profile of North India. Their arrival is often preceded by a rise in night temperatures, and their departure is typically followed by a cold wave, as clear skies allow for rapid terrestrial radiation and the influx of cold air from the snow-clad mountains Majid Hussain, Environment and Ecology, Natural Hazards and Disaster Management, p.52. Interestingly, while these systems are temperate in origin, they are essential to the agricultural and hydrological cycle of the Indian subcontinent.

Feature	Southwest Monsoon	Western Disturbances
Origin	Indian Ocean / Arabian Sea	Mediterranean Sea
Driving Force	Pressure gradient / ITCZ	Subtropical Westerly Jet Stream
Primary Season	June to September	December to March/April
Beneficiary	Kharif Crops	Rabi Crops

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Natural Hazards and Disaster Management, p.52; Certificate Physical and Human Geography, GC Leong (Oxford University press 3rd ed.), The Warm Temperate Western Margin (Mediterranean) Climate, p.181; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.34

6. Koeppen's Classification of Indian Climate (exam-level)

Wladimir Koeppen’s climate classification is the most widely used empirical system, meaning it is based on observed data—specifically, annual and monthly averages of temperature and precipitation—rather than the underlying causes like pressure belts or winds Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), World Climate and Climate Change, p.98. For India, this system provides a systematic way to map our diverse weather patterns, using capital letters to denote major climatic groups and small letters to indicate the seasonality of rainfall. In India, the most dominant categories are the 'A' (Tropical) and 'B' (Dry) climates. The 'A' group requires that the mean monthly temperature of all months be above 18°C. A unique feature of the Indian Peninsula is the 'Aw' (Tropical Savanna) climate, which covers most of the plateau south of the Tropic of Cancer. However, the coastal regions vary significantly: the West Coast is classified as 'Amw' (Monsoon type with a short dry season), while the Coromandel Coast (Tamil Nadu) is classified as 'As'. The 's' here is crucial—it stands for summer dry season, reflecting that this region stays dry during the Southwest monsoon and receives rain during the winter India Physical Environment, Geography Class XI (NCERT 2025 ed.), Climate, p.37. Moving north, the climate shifts to 'Cwg' (Humid Subtropical) across the Indo-Gangetic plains. The 'g' specifically refers to the Ganges type of temperature profile, where the maximum temperature is recorded before the summer rain (in May/June). In the extreme north and northeast, we find 'Dfc' (Cold Humid Winter) in Arunachal Pradesh and 'E' (Polar) types in the high Himalayas.

Koeppen Code	Climate Type	Region in India
Amw	Monsoon with short dry season	West Coast (south of Mumbai)
As	Monsoon with dry summer	Coromandel Coast (Tamil Nadu)
Aw	Tropical Savanna	Most of the Peninsular Plateau
Bwhw	Hot Desert	Western Rajasthan (Thar)
Cwg	Humid Subtropical (Dry winter)	Ganga Plains, Eastern Rajasthan
Dfc	Cold Humid Winter	Arunachal Pradesh

Sources: Fundamentals of Physical Geography, Geography Class XI (NCERT 2025 ed.), World Climate and Climate Change, p.98; India Physical Environment, Geography Class XI (NCERT 2025 ed.), Climate, p.37

7. Regional Anomalies in Annual Rainfall Cycles (exam-level)

While the Southwest (SW) Monsoon is the undisputed architect of India’s water security, delivering rain to the vast majority of the country between June and September, it is not a uniform blanket. In the diverse geography of India, certain regions march to the beat of a different drum. These regional anomalies are primarily driven by mountain barriers, coastline orientation, and the influence of extra-tropical weather systems.

The most striking anomaly is the Tamil Nadu coast (Coromandel Coast). While the rest of India is getting drenched in July and August, this region remains remarkably dry INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.29. This happens because of a dual disadvantage during the SW Monsoon season:

Factor	Description
Coastline Orientation	The Tamil Nadu coast is situated parallel to the Bay of Bengal branch of the SW monsoon, meaning the moisture-laden winds blow past it rather than striking it INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.37.
Rain-shadow Effect	It lies in the leeward side (rain-shadow) of the Western Ghats for the Arabian Sea branch. As the winds descend the mountains, they warm up and lose their ability to precipitate INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.37.

Instead, Tamil Nadu receives the bulk of its rainfall during the Northeast (NE) Monsoon (October to December), when retreating winds pick up moisture from the Bay of Bengal and hit the coast directly. Similarly, in the north, Jammu & Kashmir and parts of the Himalayas experience a significant rainfall peak during the winter months (December to March). This isn't from the monsoon at all, but from Western Disturbances — shallow cyclonic depressions originating over the Mediterranean Sea that bring crucial snow and rain to the northern plains and mountains INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.38. Even in the far North-East, states like Arunachal Pradesh and Assam receive some winter rainfall, though their primary peak remains the SW monsoon Geography of India, Majid Husain, Climate of India, p.19.

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.29; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.37; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Chapter 4: Climate, p.38; Geography of India, Majid Husain, Climate of India, p.19

8. Solving the Original PYQ (exam-level)

To solve this question, you must synthesize three core concepts you've just mastered: the orographic effect, the seasonal reversal of winds, and the Western Disturbances. While the Southwest (SW) monsoon is the primary rain-bearer for the Indian subcontinent, its effectiveness is not uniform. By applying the concept of the rain-shadow effect, we know that the Western Ghats block the Arabian Sea branch from reaching the Coromandel Coast. Furthermore, the latitudinal position and extratropical influences dictate that the far north receives moisture from different systems altogether. This question tests your ability to identify the geographical 'outliers' that deviate from the standard June-to-September rainfall pattern.

Walking through the logic, first examine Tamil Nadu. As detailed in INDIA PHYSICAL ENVIRONMENT (NCERT 2025 ed.), this state remains relatively dry during the SW monsoon because it lies in the rain-shadow area; instead, it waits for the Northeast (NE) monsoon (October to December) for its peak rainfall. Next, look at Jammu & Kashmir. While it receives some monsoon moisture, a significant portion of its annual precipitation comes from Western Disturbances originating in the Mediterranean during the winter months. Therefore, the set containing Tamil Nadu and Jammu & Kashmir is the only one where the SW monsoon is not the dominant source, making (D) the correct answer.

A common trap in UPSC geography is confusing total rainfall volume with rainfall source. For instance, options (A) and (C) include Rajasthan. Students often think Rajasthan doesn't receive SW monsoon rain because it is arid; however, the little rain it does receive occurs almost entirely during the SW monsoon months. Similarly, states like Arunachal Pradesh and Assam are heavily hit by the Bay of Bengal branch, while Karnataka receives torrential rain from the Arabian Sea branch. By systematically eliminating states that are directly in the path of the monsoon branches, you can avoid these distractors and focus on the unique climatic cycles of the south and the extreme north.