The Indian climate is governed by a complex interplay of Location, Relief, and Atmospheric Dynamics. These factors can be broadly categorized into two groups:
I. Factors Related to Location and Relief
1. Latitude and the Tropic of Cancer
India spans from 8°4’N to 37°6’N. The Tropic of Cancer (23.5°N) passes through the center of India (8 states).
- Tropical Zone (South): Areas south of the Tropic of Cancer lie in the tropical zone. They experience high temperatures throughout the year with a low annual range of temperature.
- Subtropical/Temperate Zone (North): Areas north of the Tropic of Cancer experience a continental climate with extreme temperatures (very hot summers and very cold winters).
2. The Himalayan Mountains
The Himalayas act as a great climatic divide.
- Shielding Effect: They protect the Indian subcontinent from the frigid, bone-chilling Central Asian winds (Siberian winds). Without the Himalayas, North India would be a cold desert.
- Rain Barrier: They act as a physical barrier to the moisture-laden Southwest Monsoon winds, forcing them to shed their moisture over the Indo-Gangetic plains and Northeast India.
3. Distribution of Land and Water
India is a peninsula surrounded by the Indian Ocean, Arabian Sea, and Bay of Bengal.
- Differential Heating: Land heats up and cools down faster than water. This creates pressure gradients that drive the seasonal reversal of winds (the essence of the Monsoon).
- Moderating Influence: Coastal areas experience an equable climate (minimal variation between summer and winter), while the interior (e.g., Delhi) faces continentality.
4. Distance from the Sea (Continentality)
As the distance from the sea increases, its moderating influence decreases.
- Regions like Amritsar or Delhi experience high diurnal and annual ranges of temperature.
- Conversely, Mumbai and Chennai remain humid and warm with little seasonal change.
5. Altitude
Temperature decreases with height at the Normal Lapse Rate (approx. 6.5°C per 1,000 meters).
- Even if they are on similar latitudes, Agra is much warmer in January than Darjeeling because of the latter’s elevation.
6. Relief and Physiography
The physical features of the land dictate rainfall distribution.
- Windward Side: The western slopes of the Western Ghats receive heavy orographic rainfall (over 250 cm).
- Leeward Side (Rain Shadow): The eastern side of the Western Ghats (e.g., the Deccan Plateau) receives scanty rainfall (less than 60 cm).
II. Factors Related to Air Pressure and Winds
1. Surface Pressure and Winds
In winter, a high-pressure center develops north of the Himalayas, blowing dry winds toward the low-pressure oceanic areas. In summer, the sun shifts to the Tropic of Cancer, creating a Low-Pressure Trough (Monsoon Trough) over Northern India, attracting moisture from the Southern Hemisphere.
2. Jet Streams and Upper Air Circulation
- Westerly Jet Stream: Flows south of the Himalayas in winter and is responsible for bringing Western Cyclonic Disturbances (winter rain for wheat crops).
- Easterly Jet Stream: Develops in summer over the Peninsula (approx. 14°N). It helps in the sudden burst of the monsoon.
3. Inter-Tropical Convergence Zone (ITCZ)
The ITCZ is a low-pressure zone where trade winds converge.
- In summer, the ITCZ shifts to the Ganga Plains (20°N-25°N). This shift is the “Monsoon Trough” which invites the Southwest Monsoon into the heart of India.
4. El Niño and La Niña (ENSO)
- El Niño: The warming of the central Pacific. It usually leads to a weak monsoon and drought in India.
- La Niña: The cooling of the central Pacific. It often results in above-average rainfall and floods in India.
5. Western Disturbances
Originating in the Mediterranean Sea, these temperate cyclones are brought into India by the Westerly Jet Stream. They provide crucial winter rainfall to Punjab, Haryana, and Western UP, which is vital for Rabi crops (Wheat).
UPSC Prelims: PYQs & Practice Questions
Previous Year Questions (PYQs)
1. With reference to the ‘Indian Ocean Dipole (IOD)’, consider the following statements: (2017)
Q:
1. IOD phenomenon is characterized by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an El Niño’s impact on the monsoon.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (b) 2 only
Explanation: Statement 1 is incorrect because IOD is the difference in sea surface temperature between the Western and Eastern Indian Ocean (not Pacific). Statement 2 is correct; a Positive IOD can mitigate the negative effects of El Niño, leading to a normal monsoon.
2. Which of the following is/are the characteristic/characteristics of Indian coal? (2013 - Relates to Climate/Geology)
Q:
1. High ash content
2. Low sulphur content
3. Low ash fusion temperature
Select the correct answer:
(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a) 1 and 2 only
Explanation: While primarily a geology question, the Gondwana coal (which India mostly has) was formed under specific climatic conditions leading to high ash but low sulphur.
Practice Questions (Prelims)
Question 1
Q: Consider the following statements regarding the Western Disturbances:
1. They originate in the Caspian Sea and are brought to India by the Easterly Jet Stream.
2. They are vital for the cultivation of Rabi crops in North-Western India.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (b) 2 only
Explanation: Statement 1 is incorrect. Western Disturbances mainly originate in the Mediterranean region and are carried towards India by the Westerlies / Subtropical Westerly Jet Stream. Statement 2 is correct as they bring winter rainfall helpful for Rabi crops in North-Western India.
Question 2
Q: Why does the Coromandel Coast receive most of its rain in winter?
(a) Due to South-West Monsoon.
(b) Due to North-East Retreating Monsoon.
(c) Due to Western Disturbances.
(d) Due to its proximity to the Equator.
Answer: (b)
Explanation: In winter (retreating monsoon season), the North-East Monsoon winds pick up moisture from the Bay of Bengal and bring rainfall to the Tamil Nadu / Coromandel Coast.
UPSC Mains – Previous Year & Practice Questions
Previous Year Questions (Mains)
Onset of Indian Monsoon vs Retreating Monsoon (General Theme)
Question: “Describe the mechanism of the onset of the Indian monsoon. How does it differ from the 'retreating' monsoon?”
Key Focus: Discuss the shift of the ITCZ and the role of the Mascarene High.
Himalayas as a Climatic Divide (General Theme)
Question: “How do the Himalayas act as a climatic divide for the Indian subcontinent? Explain with examples.”
Key Focus: Shielding from Siberian winds and trapping the SW Monsoon.
Role of Tibetan Plateau in Monsoon Intensification (General Theme)
Question: “Explain the influence of the Tibetan Plateau on the intensification of the Indian Monsoon.”
Key Focus: The Plateau as a thermal engine creating the Tropical Easterly Jet.
El Niño–La Niña and Indian Agricultural Economy (2014/2017 Theme)
Question: “Analyze the impact of El-Niño and La-Niña on the Indian agricultural economy.”
Key Focus: Droughts vs. Floods and their impact on Kharif crop yields.
Western Disturbances and Food Security (General Theme)
Question: “Discuss the significance of the 'Western Disturbances' for the food security of India.”
Key Focus: Importance of winter rain for Wheat (Rabi) in Punjab/Haryana.
Mains Practice Questions
Continentality of North India’s Climate
Question: “The 'continentality' of North India's climate is a result of both distance from the sea and the presence of the Himalayas. Elaborate.”
Jet Streams and Monsoon Burst & Withdrawal
Question: “Examine the role of 'Jet Streams' in the sudden burst and eventual withdrawal of the monsoon in India.”
Indian Ocean Dipole vs ENSO as Rainfall Predictor
Question: “Critically evaluate the 'Indian Ocean Dipole' as a more reliable predictor of Indian rainfall than the ENSO cycle.”
Factors Influencing the Climate of India- FAQs
What is the 'ITCZ' and why is it important for India?
The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt near the equator where trade winds meet. In summer, it shifts north to the Ganga Plains (becoming the Monsoon Trough), which attracts the moisture-laden winds from the Southern Hemisphere toward India.
What are 'Mango Showers' and 'Kal Baisakhi'?
These are Pre-Monsoon showers.
- Mango Showers: Occur in Kerala/Karnataka; help in ripening mangoes.
- Kal Baisakhi: Violent thunderstorms in Bengal/Assam; beneficial for tea and rice but often destructive.
Why is the Western Ghats' leeward side a rain shadow region?
As the Arabian Sea branch hits the Western Ghats, the air is forced to rise, cools, and rains on the western slope (Windward side). By the time the air crosses to the eastern side (Leeward side), it descends, warms up, and loses its ability to precipitate, creating a dry zone (e.g., Vidarbha).
How does 'Arctic Amplification' affect India?
Rapid warming in the Arctic weakens the temperature gradient between the pole and tropics, making the Jet Streams wavy. This can cause unpredictable shifts in Western Disturbances and extreme weather events in North India.
What is the 'Burst of Monsoon'?
It is the sudden arrival of heavy rainfall accompanied by violent thunder and lightning, usually in the first week of June. It is caused by the sudden northward shift of the Sub-tropical Westerly Jet Stream and the arrival of the Tropical Easterly Jet.
