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Class 9 Geography Chapter 4: Climate Notes

The chapter Class 9 Geography Chapter 4: Climate Notes explores the factors that shape India’s diverse climate. Covering topics such as monsoon patterns, seasonal variations, and weather phenomena, these notes offer a comprehensive understanding of the subject. Students can explore detailed insights into the Indian climate system, making Class 9 Geography Chapter 4: Climate Notes an essential resource for mastering this topic.



Introduction to Climate

  • Climate: Average weather conditions observed over a long period, typically 30 years or more.
  • Weather: The daily atmospheric condition concerning temperature, rainfall, and humidity.
  • Weather: The daily atmospheric condition concerning temperature, rainfall, and humidity.


Factors Affecting India’s Climate

    • India lies between 8°4’N and 37°6’N.
    • The Tropic of Cancer divides India into two distinct climate zones:
      • Tropical Zone: Areas south of the Tropic of Cancer, which have high temperatures throughout the year.
      • Subtropical Zone: Areas north of the Tropic of Cancer with greater seasonal variations in temperature.
  • Altitude:
    1. The Himalayas act as a climatic divide:
      • Prevent cold winds from Central Asia from entering India.
      • Influence the monsoonal winds by causing orographic rainfall.
    2. The coastal regions and low-lying plains have moderate climates, while high-altitude areas like Ladakh have cold and dry conditions.
  • Pressure and Wind Systems:
    1. Pressure variations in India are linked to the Inter-Tropical Convergence Zone (ITCZ), a low-pressure zone near the equator.
    2. Key wind systems include:
      • Southwest Monsoon: Brings rainfall to most parts of India.
      • Northeast Monsoon: Affects the eastern coast during October-December.
    3. High-altitude Jet Streams also play a role in influencing weather conditions.
  • Distance from the Sea:
    1. Coastal areas experience maritime influence, resulting in moderate weather conditions (e.g., Mumbai, Chennai).
    2. Interior regions experience continentality, leading to extreme temperatures (e.g., Delhi).
  • Relief Features:
    1. Relief features like mountains, plateaus, and plains influence wind patterns and precipitation.
    2. For example, the Western Ghats experience heavy rainfall due to the orographic effect, while regions on their leeward side (rain shadow areas) receive little rain.


    • The Indian Monsoon

    The monsoon is a defining feature of India’s climate. It is characterized by the seasonal reversal of winds.


    Mechanism of Monsoon
    1. Differential Heating and Cooling:
      • Land heats up faster than water, creating low pressure over the Indian subcontinent and high pressure over the surrounding seas during summer.
    2. Shifting of ITCZ:
      • The ITCZ shifts northward during summer, drawing in moisture-laden winds from the oceans.
    3. High-Pressure Areas in Southern Oceans:
      • High-pressure zones in the southern Indian Ocean direct winds toward India.
    4. Jet Streams:
      • Westerly Jet Streams over the Himalayas and Easterly Jet Streams over the Indian Ocean influence the monsoon’s onset and retreat.


    Two Types of Monsoons

    1. Southwest Monsoon (June–September):
      • The winds blow from the Indian Ocean toward the low-pressure areas of the Indian subcontinent.
      • Responsible for 75-90% of India’s annual rainfall.
      • Divided into:
        • Arabian Sea Branch: Causes heavy rainfall along the Western Ghats.
        • Bay of Bengal Branch: Brings rainfall to eastern and northeastern India.
    2. Northeast Monsoon (October–December):
      • The winds blow from the land to the sea.
      • Brings rainfall to the southeastern coastal areas, especially Tamil Nadu.


    Seasons in India

    1. Winter Season (December–February):
      • Features:
        • Low temperatures, especially in northern India.
        • Clear skies and dry weather.
      • Western Disturbances bring occasional rain to the northern plains.
      • Average temperatures:
        • Northern plains: 10°C to 15°C
        • Southern regions: above 20°C
    2. Summer Season (March–May):
      • Features:
        • High temperatures, with heat waves in northern and central India.
        • Loo winds blow over the northern plains.
      • Temperatures can rise above 40°C in many regions.
    3. Monsoon Season (June–September):
      • Features:
        • Heavy rainfall due to the Southwest Monsoon winds.
        • Uneven distribution of rainfall.
      • States like Meghalaya (Cherrapunji and Mawsynram) receive the highest rainfall.
    4. Post-Monsoon Season (October–November):
      • Features:
        • Clear skies and retreating monsoon winds.
        • Rainfall along the southeastern coast due to the Northeast Monsoon.


    Climatic Regions of India

    India has diverse climatic regions, classified as follows:

    1. Tropical Wet: Coastal regions like Kerala, Andaman & Nicobar Islands.
    2. Tropical Dry: Rajasthan and Gujarat.
    3. Tropical Wet and Dry: Central and Deccan regions.
    4. Montane Climate: Himalayan regions with cold winters.


    Impact of Climate on India

    1. Agriculture:
      • The Indian economy is monsoon-dependent, as most farming relies on rainfall.
      • Kharif crops (e.g., rice, maize) depend on the monsoon, while Rabi crops (e.g., wheat) grow in winter.
    2. Water Resources:
      • Rivers, lakes, and reservoirs are replenished during the monsoon.
    3. Economic Activities:
      • A good monsoon supports industries like textiles and sugar, whereas droughts disrupt economic stability.
    4. Disasters:
      • Variations in monsoons can lead to floods in some areas and droughts in others.


    El Niño:

    • Definition: A climate phenomenon characterized by the warming of the central and eastern Pacific Ocean near the equator.
    • Impact on Monsoon:
      • Weakens the trade winds.
      • Reduces rainfall in India, causing drought conditions.
    • Mechanism:
      • Normally, trade winds push warm water toward the western Pacific, but during El Niño, these winds weaken, and warm water accumulates in the eastern Pacific.
    • Effects on India:
      • Delayed monsoon onset.
      • Reduced agricultural output.
      • Increased temperatures and dry spells.


    La Niña:

    • Definition: The opposite of El Niño, characterized by the cooling of ocean waters in the central and eastern Pacific.
    • Impact on Monsoon:
      • Strengthens the trade winds.
      • Increases rainfall in India, sometimes leading to floods.
    • Mechanism:
      • Enhanced cooling causes stronger winds and pushes warm water farther west.
    • Effects on India:
      • Excess rainfall and potential flooding.
      • Favorable for agricultural growth in certain regions.


    Jet Streams

    • Definition: Jet streams are fast-moving air currents found at high altitudes (above 10 km) in the atmosphere, typically flowing from west to east.
    • Types:
      • Subtropical jet streams: Located around 30°N and S latitude.
      • Polar jet streams: Found at higher latitudes, near 60°N and S.
    • Characteristics:
      • Speeds can exceed 100 km/h, sometimes reaching up to 400 km/h.
      • They form at the boundaries between different air masses (cold polar air and warmer tropical air).
    • Impact:
      • Influence weather patterns, including the formation of cyclones and weather fronts.
      • Affect aviation, especially flight routes and fuel efficiency.


    Loo

    • Definition: Loo is a hot, dry, and dusty wind that blows across parts of northern India, especially during the summer months.
    • Characteristics:
      • Occurs mainly in the months of May and June.
      • The temperature can exceed 45°C, leading to intense heat.
      • Winds blow from the Thar Desert toward the plains of India.
    • Impact:
      • Causes dehydration, exhaustion, and discomfort.
      • Can lead to heat strokes and other heat-related illnesses.
      • Affects agriculture, especially crops sensitive to extreme temperatures.

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