Factors Affecting the Climate of India – UPSC Indian Geography Notes

India’s climate is categorized as a monsoon climate, prevalent primarily in Asia’s south and southeast. While there is a general uniformity in the weather pattern, regional variations exist in climatic conditions within the country. Examining the factors influencing the Climate of India is crucial for those studying Geography in preparation for the UPSC Civil Service Exam.

Indian Climate

• India’s northern part (north of the tropic of cancer) is in the temperate belt but exhibits a climate similar to that of a tropical country.
• The Himalayan ranges act as a barrier, preventing the southward movement of cold air masses from Central Asia.
• Consequently, the northern half of India experiences winters that are 3°C to 8°C warmer compared to areas at similar latitudes.
• In the southern parts of the country, the climate resembles an equatorial dry climate during the summer due to the sun’s high position.
• The north Indian plains are affected by a hot dry wind, the ‘loo,’ originating from the Thar, Baloch, and Iranian Deserts, leading to temperatures comparable to the southern regions.
• The entire Indian subcontinent south of the Himalayas is classified as a tropical country.
• India features a typical tropical monsoon climate, resulting from the seasonal reversal of winds in the Arabian Sea and Bay of Bengal.
• India’s climate is not just tropical or half temperate but is a tropical monsoon type, characterized by distinct wet and dry seasons.

Factors Affecting the Climate of India

The climate of India is shaped by a multitude of factors, which can be categorized into two main groups:

• Factors associated with location and relief
• Factors linked to air pressure and winds

Factors Related to Location and Relief

Latitude:

• The Tropic of Cancer traverses the central part of India, dividing it into the subtropical and temperate zone (north) and the tropical zone (south).
• The tropical zone, being closer to the equator, experiences high temperatures throughout the year with minimal daily and annual variations.
• Conversely, the northern region, positioned farther from the equator, exhibits an extreme climate marked by a wide daily and annual temperature range.

The Himalayan Mountains:

• The Himalayas, acting as a climatic divide, shield the subcontinent from cold northern winds and trap monsoon winds, channeling moisture across India.
• These winds originate in central and eastern Asia near the Arctic Circle.

Distribution of Land and Water:

• India is surrounded on three sides by the Indian Ocean in the south, influencing the creation of distinct air pressure zones due to differential heating of land and sea.
• Coastal areas benefit from an equable climate, while inland areas experience climate extremes.

Distance from the Sea:

• Coastal areas with large coastlines enjoy an equable climate due to the moderating influence of the sea.
• Inland regions, distant from the sea, exhibit climate extremes, impacting daily life and seasonal patterns.

Altitude:

• Higher altitudes experience lower temperatures due to thin air.
• Mountainous areas are cooler compared to plains; for instance, Agra and Darjeeling, on the same latitude, showcase notable temperature differences.

Relief:

• India’s physiography or relief influences various climatic factors such as temperature, air pressure, wind direction and speed, and rainfall distribution.
• During June-September, windward sides like the Western Ghats and Assam receive abundant rainfall, while leeward regions, like the southern plateau along the Western Ghats, remain dry.

Factors Related to Air Pressure and Wind

To comprehend the nuances of India’s local climates, it is essential to delve into the mechanics of three pivotal factors:

1. Air pressure and wind distribution on the Earth’s surface.
2. The influence of global weather-controlling factors, including the inflow of various air masses and jet streams, leading to upper air circulation.
3. The impact of the inflow of western cyclones (disturbances) during the winter season and tropical depressions during the south-west monsoon season, creating favorable conditions for rainfall.

Understanding the mechanisms of these three factors requires a detailed examination of both the winter and summer seasons throughout the year.

Mechanism of Weather in Winter Season

Surface Pressure and Winds

• Weather conditions over India are primarily influenced by the pressure distribution in Central and Western Asia during winter months.
• In winter, a high-pressure center forms north of the Himalayas.
• This high-pressure center creates a trough, leading to a low-level flow of air from the north to the Indian subcontinent, south of the mountain range.
• The surface winds from the Central Asian high-pressure center reach India as a dry continental air mass.
• In northwestern India, these continental winds collide with trade winds.
• The contact zone’s position is not stable and may occasionally shift as far east as the middle Ganga valley, bringing dry northwestern winds to the region.

Jet Stream and Upper Air Circulation

• The described air circulation pattern is observable near the earth’s surface within the lower levels of the atmosphere.
• At a higher altitude, approximately three kilometers above the earth’s surface, a different air circulation pattern emerges in the lower troposphere.
• Variations in atmospheric pressure closer to the earth’s surface do not influence the formation of upper air circulation.
• Westerly winds persist at an altitude of 9-13 km over Western and Central Asia, flowing from west to east.
• These winds, known as jet streams, traverse Asia roughly parallel to the Tibetan highlands, north of the Himalayas.
• The Tibetan highlands, acting as a barrier, cause the jet streams to bifurcate, with one branch blowing north of the Tibetan highlands and the other flowing east of the Himalayas and south of the Tibetan highlands.
• By February, the southern branch of the jet stream has a mean position at 25°N and a pressure level of 200-300 mb.
• This southern branch is believed to have a significant impact on India’s winter weather.

Western Cyclonic Disturbance and Tropical Cyclones

• The westerly jet stream carries cyclonic disturbances from the west and northwest into the Indian subcontinent during winter months.
• The onset of these cyclonic disturbances is typically heralded by a rise in the prevailing night temperature.
• Tropical cyclones take shape over the Indian Ocean and the Bay of Bengal.
• The coasts of Tamil Nadu, Andhra Pradesh, and Odisha frequently experience the impact of tropical cyclones, characterized by high wind speeds and heavy rainfall.
• These cyclones, marked by intense wind speeds and torrential rain, are often highly destructive.

Mechanism of Weather in Summer Season

Surface Pressure and Winds

• As summer approaches and the sun shifts northwards, the wind circulation over the subcontinent reverses completely at both lower and upper levels.
• By mid-July, the low-pressure belt near the surface, identified as the Inter Tropical Convergence Zone (ITCZ), moves northwards, roughly parallel to the Himalayas between 20° and 25° north latitude.

Inter-Tropical Convergence Zone (ITCZ)

• The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure zone situated near the equator, where trade winds converge, leading to the ascent of air.
• Also termed the monsoon trough, the ITCZ is positioned approximately at 20°N-25°N latitudes (over the Gangetic plain) in July.
• In winter, the ITCZ shifts southward, resulting in a reversal of winds from northeast to south and southwest, referred to as Northeast monsoons.

• By this time, the westerly jet stream exits the Indian subcontinent.
• Meteorologists have identified a connection between the northward shift of the equatorial trough and the withdrawal of the westerly jet stream from over the North Indian Plain.
• As the Inter-Tropical Convergence Zone (ITCZ) is a low-pressure zone, it attracts winds from all directions.
• After crossing the equator, the maritime tropical air mass (mT) from the southern hemisphere flows towards the low-pressure area in a general southwesterly direction.
• The term southwest monsoon is used to characterize this moist air current.

Jet Streams and Upper Air Circulation

• The described pressure and wind patterns are exclusively established in the troposphere.
• In June, an easterly jet stream traverses the southern part of the Peninsula, reaching a maximum speed of 90 kilometres per hour.
• By August, this jet stream is confined to 15°N latitudes, extending further to 22°N latitudes in September.
• In the upper atmosphere, easterlies typically do not extend north of 30°N latitude.

Easterly Jet Stream and Tropical Cyclones

• The easterly jet stream directs tropical depressions into India.
• The distribution of monsoon rainfall across the Indian subcontinent is impacted by these depressions.
• The regions experiencing the highest rainfall in India are the paths taken by these depressions.
• The frequency, direction, and intensity of these depressions passing through India play a crucial role in shaping the rainfall pattern during the southwest monsoon season.

Conclusion

India, ranked fourth among the countries most affected by climate change in 2015, is grappling with significant repercussions. Despite comprising 17% of the world’s population, the country contributes 7% of global emissions. Rising temperatures on the Tibetan Plateau are triggering the retreat of Himalayan glaciers, posing a threat to the flow rates of major rivers like the Ganges, Brahmaputra, and Yamuna. A 2007 report by the World Wide Fund for Nature (WWF) suggests that the Indus River may run dry for the same reason. The impact of climate change is evident in the increasing frequency and intensity of heat waves in India.

FAQs on Factors Affecting the Climate of India

Question 1: What is the climate of India and why is it so?

Answer: India experiences a diverse climate, but it is generally classified as a monsoon climate. This classification is attributed to the seasonal reversal of winds, influenced by factors such as the Himalayan Mountains, latitude, and the distribution of land and water. The monsoon winds play a crucial role in shaping India’s climate, bringing distinct wet and dry seasons.

Question 2: What are the features of the climate of India?

Answer: The climate of India is characterized by its diversity, encompassing tropical, subtropical, and temperate zones. Key features include the monsoon winds, the influence of the Himalayan Mountains acting as a climatic barrier, the Inter-Tropical Convergence Zone (ITCZ), and the seasonal reversal of winds. India’s climate exhibits distinct wet and dry seasons, with regional variations.

Question 3: Which is the coolest city in India?

Answer: Shimla, located in the state of Himachal Pradesh, is often considered one of the coolest cities in India. Situated in the foothills of the Himalayas, Shimla experiences a pleasant climate throughout the year, with cold winters and relatively mild summers. The city’s elevation contributes to its cool temperatures, making it a popular hill station and tourist destination.

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