Which of the following statements with regard to rainfall in India is/are correct ? 1. Most of the rainfall in India is due to the south-west monsoon. 2. In South India, rainfall decreases away from the Eastern Ghats. Select the correct answer using the code given below:

1. The Mechanism of the Indian Monsoon (basic)

To understand the Indian Monsoon, we must first look at it as a seasonal reversal of wind direction. For a long time, the classical explanation was the Thermal Concept proposed by Halley. He suggested that monsoons are simply large-scale 'land and sea breezes' Majid Husain, Climate of India, p.1. During summer, the vast Indian landmass heats up much faster than the surrounding oceans, creating a low-pressure zone over North-West India and Pakistan. This pressure vacuum pulls in the relatively cooler, moisture-laden air from the high-pressure zones over the Indian Ocean. However, modern meteorology shows the mechanism is far more complex than just heat. A critical player is the Inter-Tropical Convergence Zone (ITCZ). This is a low-pressure belt where trade winds from the Northern and Southern Hemispheres meet. In the summer (July), the ITCZ shifts northward to about 20°N-25°N latitude, positioning itself over the Gangetic Plain—this is often called the Monsoon Trough NCERT Class XI, Climate, p.30. This shift acts like a giant vacuum, encouraging the Southern Hemisphere's trade winds to cross the Equator. As these winds cross the Equator (between 40°E and 60°E), the Coriolis Force (caused by the Earth's rotation) deflects them to the right. Consequently, what were Southeast Trade winds become the South-West Monsoon. Furthermore, the final 'trigger' or 'burst' of the monsoon is linked to upper-air dynamics: the Westerly Jet Stream must move north of the Himalayas, allowing the Tropical Easterly Jet Stream to establish itself over the Indian peninsula NCERT Class XI, Climate, p.31.

Concept	Primary Driver	Focus
Classical (Thermal)	Differential Heating	Surface temperature differences between land and sea.
Modern (Dynamic)	ITCZ & Jet Streams	Atmospheric pressure belts and upper-air circulation.

Sources: Geography of India, Majid Husain, Climate of India, p.1; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.30; INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.31

2. South-West Monsoon: The Primary Rainfall Source (basic)

The South-West (SW) Monsoon is the true lifeblood of India, accounting for nearly 75% of the country’s total annual rainfall between June and September. This massive weather system is triggered by the intense heating of the Tibetan Plateau and the northward shift of the Inter Tropical Convergence Zone (ITCZ). As the moisture-laden winds from the Indian Ocean approach the Indian landmass, the tapering shape of the peninsula splits the monsoon into two distinct currents: the Arabian Sea Branch and the Bay of Bengal Branch Geography of India, Majid Husain, Climate of India, p.16.

The Arabian Sea Branch is the more powerful of the two and hits the Western Ghats first. This creates a classic orographic (mountain-induced) rainfall pattern. The western side of the Ghats (the windward side) receives torrential rain, often exceeding 400 cm, while the interior Deccan Plateau on the eastern side (the leeward side) remains relatively dry, forming a rain-shadow area INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.35. Another part of this branch moves through the Narmada and Tapi valleys to bring rain to Central India, eventually meeting the other branch in the Ganga plains.

The Bay of Bengal Branch moves towards the northeast and the Ganga plains. Unlike the Western Ghats, the Eastern Ghats are discontinuous and do not act as a primary barrier to these winds. Interestingly, during the SW monsoon, the eastern coast does not receive as much rain as the west coast from the primary winds; instead, its rainfall is often supplemented by cyclonic depressions originating in the Bay of Bengal Geography of India, Majid Husain, Climate of India, p.28. As you move from the interior rain-shadow regions toward the eastern coast, rainfall often increases again due to these maritime influences.

Feature	Arabian Sea Branch	Bay of Bengal Branch
Direction	Hits the West Coast and moves North/East.	Enters via Myanmar/Bangladesh and turns West.
Impact Area	Western Ghats, Central India, Gujarat/Rajasthan.	North-East India, West Bengal, Ganga Plains.
Intensity	Extremely high on the windward side of Ghats.	High in NE (Mawsynram) and coastal regions.

Sources: Geography of India, Majid Husain, Climate of India, p.16; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.35; Geography of India, Majid Husain, Climate of India, p.28

3. Orographic Rainfall: The Role of Western Ghats (intermediate)

To understand why India’s west coast is so lush while the interior Deccan remains relatively dry, we must look at the Orographic (Relief) Rainfall mechanism. Orographic rainfall occurs when moisture-laden winds encounter a physical barrier, like a mountain range. As the South-West Monsoon winds from the Arabian Sea strike the Western Ghats (or Sahyadris), they are forced to rise. Because these mountains are largely continuous and reach heights of 900–1600 meters, they act as a massive wall, forcing the air upward in a process called forceful upliftment CONTEMPORARY INDIA-I, Physical Features of India, p.12.

As this warm, humid air climbs the slopes, it undergoes adiabatic cooling—meaning it cools down because the atmospheric pressure decreases at higher altitudes. Once the air reaches its dew point, water vapor condenses into clouds, leading to heavy precipitation. This occurs on the windward side (the western slopes and the coastal plains), which receives a staggering 250 cm to 400 cm of rain INDIA PHYSICAL ENVIRONMENT, Climate, p.35. In contrast, the Eastern Ghats are lower (average 600m) and discontinuous, meaning they do not obstruct the monsoon winds with nearly the same intensity CONTEMPORARY INDIA-I, Physical Features of India, p.12.

Once the winds cross the crest of the Western Ghats and begin to descend on the eastern side, the opposite happens. The air compresses and warms up, increasing its capacity to hold moisture rather than releasing it. This creates a Rain-shadow area. In this region, which includes parts of Maharashtra, Karnataka, and Telangana, rainfall drops significantly because the winds have already lost most of their moisture on the western slopes INDIA PHYSICAL ENVIRONMENT, Climate, p.35.

Feature	Windward Side (Western Slopes)	Leeward Side (Eastern Slopes)
Air Movement	Rising and Cooling (Adiabatic)	Descending and Warming
Rainfall Level	Very Heavy (250–400 cm)	Low (Rain-shadow area)
Vegetation	Evergreen/Dense Tropical Forests	Dry Deciduous/Scrub Land

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.35; CONTEMPORARY INDIA-I, Geography, Class IX (NCERT 2025 ed.), Physical Features of India, p.12

4. Retreating Monsoon and North-East Flow (intermediate)

The Retreating Monsoon is a fascinating transition period in the Indian climatic calendar, occurring primarily during October and November. As the sun begins its apparent southward migration toward the Tropic of Capricorn, the intense heat that once anchored the 'Low Pressure Trough' over the Northern Plains starts to dissipate. This shift causes the monsoon trough to weaken and gradually move south, being replaced by a high-pressure system over the land. Unlike the 'burst' or sudden arrival of the monsoon in June, its withdrawal is a steady and gradual process Geography of India, Majid Husain, Climate of India, p.25. It leaves the northwestern parts of India (like Rajasthan) by early September and completely clears the Northern Plains by the beginning of October CONTEMPORARY INDIA-I, Geography, Class IX NCERT, Climate, p.32.

During this period, the weather undergoes a distinct change. The skies become clear and the clouds vanish, leading to a rise in daytime temperatures. However, because the ground is still saturated with moisture from the preceding months, the combination of high temperature and high humidity creates oppressive weather often referred to as 'October Heat'. While the days are stifling, the nights become pleasant and cool as the land begins to lose heat more effectively under clear skies CONTEMPORARY INDIA-I, Geography, Class IX NCERT, Climate, p.32.

As the low-pressure center shifts from the land to the Bay of Bengal by early November, it triggers the formation of cyclonic depressions. These cyclones often cross the eastern coast of India, bringing heavy and widespread rain to the Coromandel Coast (Tamil Nadu and Andhra Pradesh). This shift in wind direction—from land to sea—is what we call the North-East Monsoon flow. While most of India remains dry during this time, these winds pick up moisture as they cross the Bay of Bengal, making them the primary source of winter rainfall for Southeast India INDIA PHYSICAL ENVIRONMENT, Geography Class XI NCERT, Climate, p.37.

Sources: Geography of India, Majid Husain, Climate of India, p.25; CONTEMPORARY INDIA-I, Geography, Class IX NCERT, Climate, p.32; INDIA PHYSICAL ENVIRONMENT, Geography Class XI NCERT, Climate, p.37

5. Rainfall Variability and Semi-Arid Zones (exam-level)

To understand the climate of India, we must look beyond the average rainfall and focus on Rainfall Variability. In simple terms, variability refers to the degree of fluctuation in rainfall from year to year. A critical rule of thumb in Indian meteorology is that variability is inversely proportional to the total amount of rainfall. This means that areas like the North-East or the Western Coast, which receive heavy rain, have low variability (high reliability), while the semi-arid zones that receive little rain suffer from high variability (often between 30-40%), making them extremely prone to frequent droughts Geography of India, Majid Husain, Climate of India, p.43.

The creation of these Semi-Arid Zones is largely a result of orography (the influence of mountains). As the South-West monsoon strikes the Western Ghats, the windward side receives torrential rain. However, once the clouds cross the crest, the air descends, warms up, and its moisture-carrying capacity increases, leading to very little precipitation. This creates a vast Rain-Shadow Area covering the interior parts of Maharashtra (Vidarbha and Marathwada), the Karnataka Plateau, and the Rayalaseema region of Andhra Pradesh INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Natural Hazards and Disasters, p.64.

It is a common misconception that rainfall simply decreases as you move further inland from any coast. In reality, the southern peninsula experiences a U-shaped rainfall gradient during the South-West monsoon. Rainfall is high on the West Coast, drops sharply in the rain-shadow of the Western Ghats, and then actually increases again as one approaches the East Coast. This increase near the eastern seaboard is due to the influence of the Bay of Bengal branch of the monsoon and the frequent development of cyclonic depressions INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.35.

Sources: Geography of India, Climate of India, p.43; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Natural Hazards and Disasters, p.64; INDIA PHYSICAL ENVIRONMENT, Geography Class XI, Climate, p.35

6. Rainfall Gradients in Peninsular India (exam-level)

To understand the rainfall patterns in Peninsular India, we must first look at the orographic (mountain-induced) effect of the Western Ghats. As the Arabian Sea branch of the South-West monsoon hits the west coast, the Sahyadri ranges act as a massive physical barrier. These moisture-laden winds are forced to rise abruptly, cooling as they ascend. This leads to heavy precipitation on the windward side, with the Western Coastal Plains receiving between 250 cm and 400 cm of rain INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 4: Climate, p. 35.

However, once these winds cross the summit of the Western Ghats, they begin to descend. As they drop in altitude, the air warms up, which increases its capacity to hold moisture and significantly reduces humidity. This creates a rain-shadow area in the interior Deccan Plateau, where rainfall drops sharply. For example, while Mumbai or Mangaluru on the coast receive torrential rain, cities just a few hundred kilometers inland, like Pune or Bengaluru, receive substantially less CONTEMPORARY INDIA-I, Geography Class IX (2025 ed.), Climate, p. 37.

A common misconception is that rainfall simply decreases as you move away from the Eastern Ghats. In reality, the Eastern Ghats are discontinuous and low, meaning they do not act as a primary moisture barrier for the South-West monsoon. Interestingly, as you move from the semi-arid interior of the Peninsula toward the eastern coast (Odisha and Andhra Pradesh), rainfall actually increases. This is due to the influence of the Bay of Bengal branch and the frequent cyclonic depressions that strike the eastern seaboard during the monsoon season Geography of India, Majid Husain (9th ed.), Climate of India, p. 37.

Region	Rainfall Character	Primary Reason
Western Coast	Very Heavy (>250 cm)	Windward side of Western Ghats
Deccan Interior	Scanty/Low	Leeward (Rain-shadow) side
Eastern Coast	Moderate to High	Cyclonic activity & Bay of Bengal branch

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (2025 ed.), Chapter 4: Climate, p.35; CONTEMPORARY INDIA-I, Geography Class IX (2025 ed.), Climate, p.37; Geography of India, Majid Husain (9th ed.), Climate of India, p.37

7. Solving the Original PYQ (exam-level)

This question brings together two fundamental pillars of Indian climatology: the seasonal mechanism of the South-West (SW) Monsoon and the orographic influence of the Peninsular highlands. You’ve recently studied how the thermal heating of the Tibetan Plateau and the shift of the ITCZ draw moisture-laden winds from the Indian Ocean. Statement 1 is a direct application of this, confirming that the SW Monsoon is indeed the primary source of water for the subcontinent, contributing roughly 75% of India's total annual rainfall. When you see such a broad, foundational statement in UPSC, it is often correct, provided the terminology is precise.

To tackle Statement 2, you must apply the concept of orographic precipitation and the rain-shadow effect. In South India, the most dramatic rainfall gradient is created by the Western Ghats, not the Eastern Ghats. As moisture-laden winds hit the Western Ghats, heavy rain falls on the windward side, but rainfall decreases sharply as you move eastward into the leeward side (the Deccan Plateau). The Eastern Ghats are discontinuous and do not act as a major barrier for the SW monsoon in the same way; in fact, rainfall often increases as one nears the eastern coast due to moisture from the Bay of Bengal branch. Therefore, Statement 2 is a classic spatial reversal trap, a common tactic used by the UPSC to test your precision regarding geographical features.

By identifying that Statement 1 is a basic climatological fact and Statement 2 incorrectly attributes a rainfall pattern to the wrong mountain range, we arrive at the correct answer (A). Always be wary when the examiners mention specific gradients or directions—ask yourself if the physical geography supports that specific flow. According to INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT) and the IMD Monsoon Report, the primary moisture barrier in the south is the Western Ghats, making Statement 2 factually incorrect.