Climate

Introduction to Climate

Definition:
Climate refers to the long-term average weather conditions observed over a significant period, usually 30 years, for a particular region. It is influenced by various factors such as latitude, altitude, ocean currents, winds, and proximity to water bodies.

Mechanism:
Climate is different from weather, which refers to short-term atmospheric conditions. While weather can change rapidly, climate indicates trends and patterns over a much longer duration. For India, the climate is influenced by the tropical position, the Himalayas, the monsoon winds, and the surrounding seas.

Examples:

• Tropical climates in the southern part of India.
• Temperate climates in the higher altitude regions like the Himalayan ranges.

Factors Influencing Climate

Several factors determine the climate of a region:

• Latitude: The position of a place relative to the equator affects the amount of solar radiation it receives. For instance, regions closer to the equator (like Kerala) experience a tropical climate with high temperatures and rainfall, while those near the poles experience colder temperatures.
• Altitude: Higher altitudes have cooler temperatures. Himalayan regions and areas like Shimla experience a temperate climate due to their altitude.
• Pressure and Winds: The distribution of air pressure leads to wind patterns, which in turn influence rainfall and temperature. The southwest monsoon winds bring rainfall to the Indian subcontinent during the summer.
• Distance from Sea: Coastal regions like Mumbai and Chennai have a moderate climate due to the thermal stability of the seas. The interiors of the country, such as Rajasthan, experience an extreme climate.
• Ocean Currents: The Indian Ocean’s currents play a significant role in shaping the coastal climate. For example, the cold Benguela Current reduces temperatures along the west coast of Africa, whereas the warm Agulhas Current has a warming effect.

Example:

• Coastal areas like Mumbai experience a tropical maritime climate, with moderate temperatures and humidity due to proximity to the Arabian Sea.
• The Thar Desert experiences an arid climate due to its distance from the sea and low rainfall.

Types of Climate in India

India experiences several distinct types of climates due to its vast size and geographical diversity:

• Tropical Wet Climate: Found in the southwestern coast and the Western Ghats, this climate experiences heavy rainfall throughout the year. The regions like Kerala and parts of the western coast come under this climate.
• Tropical Dry Climate: Found in areas like Rajasthan, Gujarat, and parts of the Deccan Plateau, it is characterized by extreme heat in summer and very little rainfall throughout the year.
• Subtropical Climate: Found in the northern plains of India, such as Delhi, Punjab, and Uttar Pradesh, characterized by hot summers, moderate winters, and a seasonal monsoon.
• Temperate Climate: Present in the hilly regions of the Himalayas and parts of the northeastern states, this climate experiences cooler temperatures and varied rainfall depending on the altitude.
• Mountain Climate: In regions like Ladakh and other higher altitude areas of the Himalayas, the climate is harsh, with cold winters and cooler summers.

Example:

• The tropical wet climate is seen in Kerala, with high humidity and rainfall.
• The tropical dry climate is predominant in Rajasthan, characterized by high temperatures and dry conditions.

Theories of Monsoon

The monsoon system is one of the most complex climatic phenomena, influencing the weather and agriculture of India. Over the years, different theories have been proposed to explain the mechanism behind the monsoon. These theories can be broadly classified into four major types:

1. Classical Theory (Thermal Concept)
2. Dynamic Theory (Jet Stream Theory)
3. Equatorial Westerly Theory
4. Modern Theory (ITCZ and El Niño-Southern Oscillation Theory)

1.Classical Theory (Thermal Concept) – Halley’s Theory (1686)

Definition:
The Classical Theory of Monsoon, proposed by Edmund Halley, explains the monsoon as a large-scale land-sea breeze caused by differential heating of land and ocean.

Mechanism:

• During summer, the Indian subcontinent heats up rapidly, creating a low-pressure area over North India.
• The Indian Ocean, being relatively cooler, has high pressure.
• The pressure gradient causes moisture-laden southwest winds from the ocean to blow towards the Indian landmass, bringing rainfall (Southwest Monsoon).
• During winter, the land cools faster, creating a high-pressure area over India, while the Indian Ocean remains relatively warmer.
• Winds reverse direction, blowing from the land (high pressure) to the sea (low pressure), resulting in dry northeast monsoon winds.

Limitations:

• This theory considers only thermal factors and does not explain the variability in monsoon intensity.
• It does not account for the onset, variability, and withdrawal of monsoons.
• The role of upper atmospheric circulation, jet streams, and El Niño is ignored.

Example:

• Southwest Monsoon (June-September): Moist air from the Indian Ocean moves towards India due to low pressure, causing heavy rainfall.
• Northeast Monsoon (October-December): High pressure over North India leads to dry winds flowing towards the ocean, affecting Tamil Nadu.

2. Dynamic Theory (Jet Stream Theory) – Flohn’s Theory (1950s)

Definition:
This theory explains the monsoon as a result of the shifting of subtropical westerly jet streams (STWJ) and the development of the tropical easterly jet stream (TEJ).

Mechanism:

• Winter Season:
  • The Subtropical Westerly Jet Stream (STWJ) flows over India from west to east.
  • This jet stream prevents the development of a low-pressure system, maintaining dry conditions in winter.
• Summer Season:
  • With the onset of summer, the ITCZ (Inter-Tropical Convergence Zone) shifts northward, pulling the STWJ towards Tibet.
  • The absence of STWJ over India allows the development of a low-pressure area, inviting moist southwest monsoon winds.
  • A new Tropical Easterly Jet Stream (TEJ) develops over the Indian subcontinent, strengthening the monsoon currents.

Limitations:

• The theory explains the onset of monsoon but not the breaks in monsoon.
• It does not explain regional variations in monsoon rainfall.
• The role of ENSO (El Niño-Southern Oscillation) and Indian Ocean Dipole (IOD) is not considered.

Example:

• The 2009 monsoon failure in India was linked to abnormal jet stream movement.
• The Western Disturbances, which cause winter rainfall in North India, are associated with STWJ.

3. Equatorial Westerly Theory – Findlater’s Theory (1969)

Definition:
This theory states that the monsoon winds originate due to the deflection of equatorial westerlies, which shift towards India due to Coriolis force and the Himalayas.

Mechanism:

• The normal trade winds flow from east to west in both hemispheres.
• Near the equator, these trade winds meet at the ITCZ, creating equatorial westerlies.
• Due to the northward shift of the ITCZ in summer, the equatorial westerlies also shift northward, becoming the southwest monsoon winds.
• The Himalayas act as a barrier, forcing the monsoon winds to deflect and rise, leading to orographic rainfall.

Limitations:

• The theory does not explain why monsoons weaken or fail in certain years.
• It does not account for the role of ENSO, Jet Streams, and Ocean Currents.

Example:

• The onset of the southwest monsoon over the Western Ghats is due to the orographic lifting of monsoon winds.

4. Modern Theory (ITCZ and El Niño-Southern Oscillation Theory – ENSO & IOD Impact)

Definition:
The modern theory integrates ITCZ movement, Jet Streams, ENSO (El Niño-Southern Oscillation), and Indian Ocean Dipole (IOD) to explain monsoon variability.

Mechanism:

1. ITCZ Shift:
   • In summer, the ITCZ shifts northward, bringing moist monsoon winds.
   • In winter, it shifts southward, leading to dry conditions.
2. ENSO Effect:
   • El Niño: Warmer-than-usual Pacific waters cause weaker monsoon and droughts in India.
   • La Niña: Cooler-than-usual Pacific waters strengthen the monsoon, leading to above-normal rainfall.
3. Indian Ocean Dipole (IOD):
   • Positive IOD: Warmer waters near the western Indian Ocean enhance monsoon rainfall.
   • Negative IOD: Cooler waters near the western Indian Ocean reduce monsoon intensity.
4. Role of Jet Streams:
   • The Tropical Easterly Jet Stream (TEJ) strengthens the monsoon.
   • The Westerly Jet Stream (WJS) in winter prevents monsoon development.

Limitations:

• This theory is complex and requires real-time meteorological data for accurate predictions.
• It does not explain sudden breaks in monsoon rainfall.

Example:

• The 2015 drought in India was due to El Niño, which weakened monsoon currents.
• The 1997 La Niña year brought excessive monsoon rainfall.

Conclusion:

Each monsoon theory contributes to understanding different aspects of the monsoon mechanism. While Halley’s Classical Theory explains the basic land-sea interaction, Flohn’s Jet Stream Theory highlights the role of upper atmospheric winds. Findlater’s Equatorial Westerly Theory emphasizes wind deflection, and the Modern Theory integrates global climatic phenomena like ENSO and IOD to provide a holistic view.

Seasons in India

India experiences distinct seasons due to its location and varying climate factors:

• Winter (December to February): This season is characterized by cooler temperatures, particularly in the northern plains, while southern India remains relatively warmer. The western disturbance causes rainfall in the north-western states.
• Summer (March to June): The temperature rises sharply, with some areas reaching extreme highs. The Thar Desert witnesses extremely high temperatures.
• Monsoon (June to September): The onset of the southwest monsoon brings widespread rainfall to most parts of India, with a marked variation in intensity.
• Post-Monsoon (October to November): The monsoon winds retreat, leading to dry weather and a reduction in rainfall.

Example:

• The summer season in Delhi can reach temperatures as high as 45°C, while during winter, temperatures may drop to as low as 5°C.
• Kerala’s monsoon lasts from June to September, while Tamil Nadu experiences it from October to December.

Climate Change and Its Impact on India

Definition:
Climate change refers to the long-term alteration of temperature and typical weather patterns in a place, caused primarily by human activities like burning fossil fuels, deforestation, and industrial emissions.

Mechanism:
Rising global temperatures have led to increased frequency of extreme weather events such as cyclones, heatwaves, and heavy rainfall in many parts of India. The melting of glaciers in the Himalayas has also led to an increased risk of floods and the disruption of water supplies for millions.

Impact on India:

• Increased Temperature: India has been experiencing hotter summers, with some regions witnessing temperature spikes of up to 50°C.
• Flooding: Increased monsoon rainfall, coupled with rising sea levels, has resulted in severe flooding, particularly in coastal areas.
• Droughts: Some regions, particularly in the northwest and parts of central India, face recurrent droughts due to erratic rainfall patterns.

Example:

• The 2019 floods in Kerala and parts of Karnataka are attributed to heavy monsoon rainfall intensified by climate change.
• The 2015 heatwave in India led to over 2,000 deaths, with temperatures soaring past 45°C in many states.

Climatic Regions of India (Köppen Climate Classification)

Definition:
The Köppen climate classification system divides the world into five broad types of climate, based on temperature and precipitation patterns. India’s climate is classified into tropical, temperate, and polar zones.

Mechanism:

• Tropical Wet (Am): Found in the southern coastal regions, characterized by high humidity and year-round rainfall.
• Tropical Dry (Aw): Predominant in the northern and central regions with distinct wet and dry periods.
• Warm Temperate (Cw): Found in parts of the northern plains, marked by moderate temperatures and seasonal rainfall.
• Cool Temperate (Cf): Seen in the Himalayan region, characterized by cooler temperatures and heavy snowfall in winter.

Example:

• The climate in Delhi is classified as tropical wet and dry (Aw) under the Köppen system.
• Coastal areas like Mumbai fall under tropical wet (Am) with high rainfall.

Impact of the Himalayas on Indian Climate

Definition:
The Himalayas play a crucial role in shaping the climate of the Indian subcontinent by acting as a barrier to cold Arctic winds and influencing the monsoon system.

Mechanism:

• Blocking Cold Winds: The Himalayas prevent the cold polar winds from entering the Indian subcontinent, creating a temperate climate in the northern plains.
• Monsoon Influence: The mountain range forces the monsoon winds to rise, resulting in heavy rainfall on the windward side (western Himalayas) and dry conditions on the leeward side (in rain shadow areas like Ladakh and parts of Himachal Pradesh).

Example:

• The high rainfall in places like Mandi and Kullu in Himachal Pradesh due to the orographic effect of the Himalayas.
• Ladakh remains dry due to its location in the rain shadow region.

Impact of the Indian Ocean on Climate

Definition:
The Indian Ocean plays a significant role in shaping the climate of the Indian subcontinent by influencing the monsoon and creating a humid maritime climate along the coast.

Mechanism:
The warm waters of the Indian Ocean are a significant source of moisture for the southwest monsoon winds. The ocean currents affect coastal temperature regulation, preventing drastic temperature variations between day and night.

Example:

• The Arabian Sea contributes to heavy rainfall in the western coast during the monsoon.
• The Bay of Bengal influences the weather patterns in the eastern coastal regions, particularly Tamil Nadu.

Conclusion

India’s climate is highly diverse due to the country’s vast size and varied geographical features. The combination of tropical monsoon winds, the Himalayas, the Indian Ocean, and latitude influences the diverse climates found within India. These climatic variations directly affect agriculture, water resources, and the daily lives of people across the subcontinent.

Example:

• The monsoon is vital for Indian agriculture, especially rice and wheat cultivation in the northern plains.
• The impact of climate change has led to challenges in water management and agriculture, especially in drought-prone areas like Maharashtra and Rajasthan.

MCQ Practice

1. Consider the following statements regarding climate:

1. Climate refers to short-term atmospheric conditions observed over a few days.
2. Weather refers to long-term average weather patterns observed over decades.
3. Climate is influenced by factors such as latitude, altitude, ocean currents, and winds.

Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 3 only
(c) 1 and 3 only
(d) 2 and 3 only

Answer: (b) 3 only

Explanation: Climate refers to long-term weather patterns (usually over 30 years), whereas weather refers to short-term conditions. Therefore, statements 1 and 2 are incorrect, and only statement 3 is correct.

2. With reference to factors influencing climate, consider the following statements:

1. Higher altitudes experience cooler temperatures.
2. Proximity to the sea results in extreme temperature variations.
3. Ocean currents can influence coastal climates by altering temperatures.

Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 1 and 3 only

Explanation: Higher altitudes experience lower temperatures (statement 1 is correct). Ocean currents influence temperature and climate along the coast (statement 3 is correct). However, proximity to the sea moderates temperature variations rather than causing extreme ones (statement 2 is incorrect).

3. Which of the following climatic types is correctly matched with its corresponding region in India?

1. Tropical Wet Climate – Rajasthan
2. Tropical Dry Climate – Kerala
3. Subtropical Climate – Northern Plains

Select the correct answer using the codes below:
(a) 1 and 2 only
(b) 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 3 only

Explanation:

• Tropical Wet Climate is found in Kerala, not Rajasthan (statement 1 is incorrect).
• Tropical Dry Climate is found in Rajasthan and Gujarat, not Kerala (statement 2 is incorrect).
• Subtropical Climate is found in the northern plains like Delhi and Punjab (statement 3 is correct).

4. Consider the following statements regarding Halley’s Classical Theory of Monsoon:

1. The monsoon is caused by the differential heating of land and ocean.
2. The southwest monsoon occurs due to high pressure over the Indian subcontinent.
3. The northeast monsoon is caused by winds moving from land to sea.

Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 1 and 3 only

Explanation:

• The theory explains that monsoons occur due to differential heating of land and sea (statement 1 is correct).
• The southwest monsoon is caused by low pressure over land, not high pressure (statement 2 is incorrect).
• The northeast monsoon is caused by winds moving from land to sea during winter (statement 3 is correct).

5. Which of the following factors play a role in the Indian monsoon system?

1. Jet Streams
2. Inter-Tropical Convergence Zone (ITCZ)
3. El Niño-Southern Oscillation (ENSO)
4. Ocean Currents

Select the correct answer using the codes below:
(a) 1 and 2 only
(b) 1, 2, and 3 only
(c) 2, 3, and 4 only
(d) 1, 2, 3, and 4

Answer: (d) 1, 2, 3, and 4

Explanation: The Indian monsoon is influenced by Jet Streams (upper atmospheric winds), ITCZ (which shifts northward in summer), ENSO (El Niño weakens monsoon, La Niña strengthens it), and ocean currents (which impact coastal climates and rainfall patterns).

6. With reference to the Equatorial Westerly Theory of Monsoon, consider the following statements:

1. It explains that monsoon winds originate due to the deflection of equatorial westerlies.
2. The Himalayas play no role in this theory.
3. It accounts for El Niño’s impact on the monsoon.

Which of the above statements is/are correct?
(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 only

Explanation: The Equatorial Westerly Theory explains that monsoon winds form due to deflection of equatorial westerlies (statement 1 is correct). The Himalayas play a role in deflecting these winds (statement 2 is incorrect). The theory does not consider El Niño’s role (statement 3 is incorrect).

7. Consider the following statements regarding the Indian monsoon:

1. La Niña leads to weaker monsoon rainfall in India.
2. Positive Indian Ocean Dipole (IOD) strengthens the monsoon.
3. The Inter-Tropical Convergence Zone (ITCZ) shifts southward during summer.

Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 2 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 2 only

Explanation:

• La Niña strengthens the Indian monsoon, not weakens it (statement 1 is incorrect).
• A positive IOD leads to more monsoon rainfall in India (statement 2 is correct).
• The ITCZ shifts northward during summer, not southward (statement 3 is incorrect).

8. Which of the following is NOT an impact of climate change on India?

(a) Increase in heatwaves
(b) Reduction in cyclones
(c) More frequent droughts
(d) Melting of Himalayan glaciers

Answer: (b) Reduction in cyclones

Explanation: Climate change has increased the frequency and intensity of cyclones, not reduced them. Other impacts include heatwaves, droughts, and glacier melting.

9. Consider the following pairs of climatic regions and their Köppen classification:

1. Mumbai – Tropical Wet (Am)
2. Rajasthan – Tropical Dry (Aw)
3. Delhi – Cool Temperate (Cf)

Which of the above pairs is/are correctly matched?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (a) 1 and 2 only

Explanation:

• Mumbai has a Tropical Wet (Am) climate (correct).
• Rajasthan has a Tropical Dry (Aw) climate (correct).
• Delhi has a Tropical Wet and Dry (Aw) climate, not Cool Temperate (Cf) (incorrect).

10. Which of the following is an effect of the Himalayas on India’s climate?

1. It blocks cold winds from Central Asia, keeping northern India warmer in winter.
2. It prevents the southwest monsoon from reaching India.
3. It causes heavy rainfall on the windward side and dry conditions on the leeward side.

Select the correct answer using the codes below:
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2, and 3

Answer: (b) 1 and 3 only

Explanation: The Himalayas block cold winds, keeping North India warmer (statement 1 is correct). They help in monsoon rainfall, not prevent it (statement 2 is incorrect). The windward side gets more rain, while the leeward side remains dry (statement 3 is correct).