Which one of the following causes rainfall in the north-western parts of India during Winter Season ?

1. The Four Seasons of India: An Overview (basic)

To understand the complex Indian Monsoon, we must first look at the rhythm of the Indian year. India’s climate is characterized by a distinct seasonal rhythm, where weather elements like temperature, pressure, and wind direction change in a predictable cycle. While we often think of the year in four main blocks, the Indian Meteorological Department (IMD) officially recognizes four major seasons, and the Indian cultural tradition beautifully identifies six smaller divisions known as Ritus. India Physical Environment, Climate, p.38. These seasons are not uniform across the country; for instance, while North India experiences sharp contrasts between a freezing winter and a scorching summer, Peninsular India enjoys a more equable, maritime climate with very little temperature variation throughout the year. India Physical Environment, Climate, p.37.

The four primary meteorological seasons of India are:

• The Cold Weather Season (Winter): Lasting from December to February. It is characterized by clear skies, low humidity, and the influence of Western Disturbances—extra-tropical storms from the Mediterranean that bring crucial winter rain to the northwest plains and snow to the Himalayas. Geography of India, Climate of India, p.18.
• The Hot Weather Season (Summer): From March to May. As the sun moves northwards toward the Tropic of Cancer, temperatures soar across the northern plains, leading to localized storms like Loo or Kalbaishakhi.
• The Southwest Monsoon Season (Rainy): From June to September. This is the lifeblood of Indian agriculture, where moisture-laden winds from the Indian Ocean sweep across the subcontinent.
• The Season of Retreating Monsoon (Autumn): Occurring in October and November. As the monsoon winds withdraw, this serves as a transition period marked by clear skies but high humidity (often called 'October Heat') and cyclonic activity on the eastern coast.

Interestingly, the traditional Indian calendar divides the year into six seasons (Vasanta, Grishma, Varsha, Sharada, Hemanta, and Shishira), each lasting roughly two months. India Physical Environment, Climate, p.38. While the modern meteorological four-season model is vital for scientific study and flight/maritime planning, the traditional six-season cycle remains deeply embedded in the agricultural and cultural practices of North and Central India.

Region	Climate Characteristic	Key Feature
North India	Continental Type	Extreme heat in summer, extreme cold in winter.
South India	Maritime Type	Moderate temperatures; lack of a well-defined winter.

Sources: India Physical Environment, Climate, p.37; India Physical Environment, Climate, p.38; Geography of India, Climate of India, p.18

2. Atmospheric Circulation: Pressure Belts and ITCZ (intermediate)

To understand the Indian Monsoon, we must first master the concept of Atmospheric Circulation. At its heart, air moves from areas of High Pressure to Low Pressure. Around the Earth's equator, where the sun's rays are most direct, the air heats up, becomes less dense, and rises. This creates a permanent belt of low pressure known as the Inter-Tropical Convergence Zone (ITCZ). INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.30. The ITCZ is the 'meeting ground' where the Northeast trade winds from the Northern Hemisphere and the Southeast trade winds from the Southern Hemisphere converge and ascend.

The most critical thing to remember is that the ITCZ is not stationary. Because the Earth is tilted, the area of maximum heating shifts north and south with the seasons. In July (summer in the Northern Hemisphere), the ITCZ moves northwards, positioning itself around 20°N-25°N latitudes, right over the Gangetic Plain. INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.34. In this position, it is often called the Monsoon Trough. This low-pressure trough acts like a giant vacuum, pulling in air from the surrounding regions to fill the void.

When the ITCZ shifts so far north, the Southeast Trade Winds from the Southern Hemisphere are literally pulled across the Equator. As they cross the Equator, the Coriolis Force (caused by Earth's rotation) deflects them to the right. These diverted winds then enter the Indian subcontinent from the southwest, giving us the famous Southwest Monsoon. CONTEMPORARY INDIA-I, Geography, Class IX . NCERT(Revised ed 2025), Climate, p.28. Conversely, in winter, the ITCZ moves south of the Equator, leading to a reversal of winds known as the Northeast Monsoon. Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Pressure Systems and Wind System, p.314.

Feature	Summer (July)	Winter (January)
ITCZ Position	Over North India (20°N-25°N)	South of the Equator
Pressure over India	Low Pressure (Monsoon Trough)	High Pressure (North of Himalayas)
Wind Direction	Southwest to Northeast	Northeast to Southwest

Sources: INDIA PHYSICAL ENVIRONMENT, Geography Class XI (NCERT 2025 ed.), Climate, p.30, 34; CONTEMPORARY INDIA-I, Geography, Class IX . NCERT(Revised ed 2025), Climate, p.28; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Pressure Systems and Wind System, p.314

3. Jet Streams: The Subtropical Westerly Jet (intermediate)

To understand the Indian monsoon, we must first look at the sky—specifically, high into the upper troposphere. Jet Streams are narrow bands of fast-moving air (often exceeding 180 km/h) that circle the globe. In the context of India, the most influential is the Subtropical Westerly Jet (STWJ). During the northern winter, as the sun moves south, this jet stream also shifts toward the equator, positioning itself between 20°N and 35°N latitudes Majid Husain, Geography of India, Chapter 4, p.8.

A fascinating geographical phenomenon occurs when this jet stream encounters the massive physical barrier of the Himalayas and the Tibetan Plateau. The jet is forced to bifurcate (split) into two distinct branches. One branch flows to the north of the Tibetan Plateau, while the other flows to the south of the Himalayas, directly over the Indo-Gangetic plains. This southern branch is a key driver of India's winter weather. It acts as a high-altitude "conveyor belt" that steers Western Disturbances—extratropical storms originating over the Mediterranean Sea—into Northwest India NCERT Class IX, Contemporary India-I, Chapter 4, p.27. These disturbances bring the crucial winter rain and mountain snow that sustain Rabi crops like wheat.

The transition from winter to summer is equally dramatic. As the Tibetan Plateau begins to heat up in late spring, the southern branch of the STWJ becomes unstable. For the Southwest Monsoon to truly "burst" over India, this southern branch must completely withdraw from the Indian plains and shift north of the Himalayas NCERT Class XI, India Physical Environment, Chapter 4, p.31. This northward shift acts like the opening of a gate, allowing the low-level monsoon winds to rush in and occupy the space previously dominated by the sinking air of the westerly jet.

Feature	Winter Position	Summer Position
STWJ Location	Bifurcated; Southern branch over North India	Shifted north of the Tibetan Plateau (approx. 40°N)
Weather Impact	Brings Western Disturbances (Rain/Snow)	Withdrawal allows the Summer Monsoon to set in

Sources: Geography of India, Chapter 4: Climate of India, p.8; Contemporary India-I, Geography Class IX, Chapter 4: Climate, p.27; India Physical Environment, Geography Class XI, Chapter 4: Climate, p.31

4. Distinguishing the Retreating Monsoon (intermediate)

The Retreating Monsoon season (October and November) represents a transition phase between the hot-wet rainy season and the cool-dry winter. This retreat is triggered by the southward migration of the sun toward the Tropic of Capricorn. As the sun moves south, the intense low-pressure trough over the Ganga plains weakens and begins to shift southward in response. Consequently, the moisture-laden Southwest Monsoon winds start losing their grip and begin to withdraw from the landmass India Physical Environment, NCERT Class XI, Climate, p.37. Unlike the 'burst' of the monsoon, which is often sudden, the retreat is steady and gradual Geography of India, Majid Husain, Climate of India, p.25.

The geography of withdrawal follows a specific pattern: it begins in North-western India (Punjab and Rajasthan) by early September because these areas are the furthest from the oceanic moisture source. By mid-October, the monsoon typically leaves the northern half of the Indian peninsula. A peculiar feature of this season is 'October Heat'—the combination of high temperatures and high humidity caused by the recently soaked ground and clear skies, which makes the weather rather oppressive. However, as the low-pressure system shifts completely into the Bay of Bengal by early November, it often manifests as cyclonic depressions that hit the eastern coast India Physical Environment, NCERT Class XI, Climate, p.37.

Crucially, as the winds reverse and blow from the northeast (the North-East Monsoon), they travel over the Bay of Bengal, picking up moisture. This moisture is then released as torrential rainfall along the Coromandel Coast (Tamil Nadu) and parts of Andhra Pradesh, which would otherwise remain dry during the summer monsoon India Physical Environment, NCERT Class XI, Climate, p.34. In the Northwest, a different phenomenon occurs during the peak winter: Western Disturbances. These are extra-tropical storms from the Mediterranean that bring the small but vital 'Mahawat' (winter rain) to the plains, which is essential for the Rabi crops like wheat Contemporary India-I, NCERT Class IX, Climate, p.28.

Feature	Southwest Monsoon (Advancing)	Retreating Monsoon (Transition)
Wind Direction	South-West to North-East (Sea to Land)	North-East to South-West (Land to Sea)
Primary Region	Most of mainland India	Tamil Nadu Coast, Andhra Pradesh
Atmospheric Pressure	Low pressure over Northern India	Low pressure shifts to Bay of Bengal

Sources: India Physical Environment, NCERT Class XI, Climate, p.37; Geography of India, Majid Husain, Climate of India, p.25; India Physical Environment, NCERT Class XI, Climate, p.34; Contemporary India-I, NCERT Class IX, Climate, p.28

5. Agricultural Impact: Rabi Crops and 'Mahawat' (basic)

While the Southwest Monsoon is the primary driver of Indian agriculture, the winter season brings a subtle but critical phenomenon known as 'Mahawat'. This refers to the light rainfall received in the North-Western plains of India (such as Punjab, Haryana, and Rajasthan) during the winter months. This moisture is brought to India by Western Disturbances—shallow cyclonic depressions that originate in the Mediterranean region and are steered toward the subcontinent by the subtropical westerly jet stream CONTEMPORARY INDIA-I, Geography, Class IX, p.28. While this rainfall is small in volume (often ranging between 3 and 7 cm), its timing makes it disproportionately valuable for the agricultural economy.

The primary beneficiary of 'Mahawat' is the Rabi crop cycle, specifically winter cereals like Wheat. Wheat thrives in the cool, moist weather provided by these disturbances. According to agricultural principles, wheat requires a moderate temperature of about 16°C and a growing period of about 90 days Certificate Physical and Human Geography, GC Leong, Agriculture, p.252. A crucial aspect of this winter rain is its occurrence just before the harvest; even a small amount of moisture at this stage swells the grains, significantly improving the quality and weight of the yield.

However, it is important to distinguish between the natural benefit of 'Mahawat' and the intensive farming practices of the region. Because the winter rainfall is statistically low, heavy irrigation remains the backbone of high-yield wheat production. For instance, in states like Punjab and Haryana, over 97% of the wheat-growing area is irrigated to ensure stability against the unpredictability of these winter storms Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.19.

Feature	Description
Origin	Mediterranean Region (Western Disturbances)
Local Name	Mahawat
Primary Crop	Rabi crops (especially Wheat)
Benefit	Swells the grains before harvest, increasing yield

Sources: CONTEMPORARY INDIA-I, Geography, Class IX, Climate, p.28; Certificate Physical and Human Geography, GC Leong, Agriculture, p.252; Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.19

6. Western Disturbances: Origin and Path (exam-level)

Western Disturbances are low-pressure systems or extra-tropical cyclonic storms that originate in the Mediterranean region. During the winter, as the sun moves south of the equator, the global pressure belts also shift southward. This brings the Mediterranean basin under the influence of the Westerlies, which facilitate the formation of these cyclonic systems GC Leong, Certificate Physical and Human Geography, p.182. Unlike the violent tropical cyclones of the summer, these are temperate cyclones born from the interaction of contrasting air masses in the mid-latitudes PMF IAS, Physical Geography, p.410.

The path of these disturbances is determined by the Subtropical Westerly Jet Stream (STWJ), a high-altitude wind that flows from west to east. This jet stream acts as a conveyor belt, steering the disturbances across West Asia (Iran, Iraq, and Afghanistan). During this transit, the systems pick up additional moisture from the Caspian Sea and the Black Sea before finally arriving at the northwestern borders of the Indian subcontinent.

When these disturbances reach India, the Himalayas act as a massive physical barrier, forcing the moist air to ascend (orographic lift) and cool. This results in winter rainfall in the plains of Punjab, Haryana, and Rajasthan, and heavy snowfall in the Western Himalayas like Jammu & Kashmir and Himachal Pradesh Majid Husain, Geography of India, Chapter 4, p.18. Although the volume of rain is relatively low, it is extremely beneficial for the Rabi crops, specifically winter cereals like wheat.

Feature	Western Disturbances	Tropical Cyclones
Origin	Mediterranean Region (Extra-tropical)	Tropical Oceans (e.g., Bay of Bengal)
Steering Mechanism	Subtropical Westerly Jet Stream	Easterly Trade Winds
Season in India	Winter (December to February)	Pre-monsoon and Post-monsoon

Sources: Certificate Physical and Human Geography, GC Leong, The Warm Temperate Western Margin (Mediterranean) Climate, p.182; Physical Geography by PMF IAS, Manjunath Thamminidi, Temperate Cyclones, p.410; Geography of India, Majid Husain, Climate of India, p.18

7. Solving the Original PYQ (exam-level)

This question tests your ability to bridge the gap between global atmospheric circulation and local weather patterns. Having just studied the movement of Air Masses and Jet Streams, you can now see how these building blocks interact. During the winter, the Subtropical Westerly Jet Stream shifts southward, positioned right over the Indian subcontinent. This jet stream acts as a high-altitude conveyor belt, steering extra-tropical Western disturbances—which originate in the Mediterranean region—towards the Indian landmass. As these low-pressure systems travel across West Asia, they pick up moisture from the Mediterranean, Black, and Caspian Seas, eventually discharging it as vital winter rainfall across the plains of Punjab, Haryana, and Rajasthan, and as snow in the Western Himalayas.

To arrive at the correct answer, (C) Western disturbances, you must focus on the specific geographical and temporal markers: North-western India and Winter Season. This precipitation is distinct from the regular monsoon and is often referred to as "winter gold" because of its critical role in the survival of Rabi crops, particularly wheat. As detailed in Geography of India by Majid Husain, these disturbances are the primary reason the North-West does not remain completely arid during the cold months, unlike the rest of the country which is under the influence of dry continental winds.

UPSC uses the other options as classic traps to test your precision. The South West monsoon is strictly a summer phenomenon (June–September), while the Retreating monsoon (October–November) primarily affects the South-Eastern coast or the Coromandel region, not the North-West. Furthermore, while Cyclonic depressions do cause significant rainfall, in the Indian context, they are usually associated with the Bay of Bengal and impact the eastern coastal states during the transition seasons. By recognizing that only the Western disturbances originate from the west and arrive during peak winter, you can confidently eliminate the distractors.