Class 11 Geography Notes Chapter 4 (Climate) – India Physical Environment Book

Detailed Notes with MCQs of Chapter 4, 'Climate,' from your 'India: Physical Environment' book. This chapter is absolutely crucial, not just for understanding India's geography but also because questions frequently appear from this section in various government exams. Pay close attention as we break it down.

Chapter 4: Climate - Detailed Notes

1. Introduction: Climate vs. Weather

• Weather: Refers to the state of the atmosphere over an area at any specific point in time (short-term: day, week). Elements include temperature, pressure, wind, humidity, precipitation.
• Climate: Refers to the sum total of weather conditions and variations over a large area for a long period (typically > 30 years). It represents the average weather.
• India's Climate: Broadly described as 'Monsoon' type. The word 'Monsoon' derives from the Arabic word 'mausim,' meaning season, referring to the seasonal reversal in wind direction.
• Unity and Diversity: While India has a broadly monsoon climate, there are significant regional variations in temperature and precipitation patterns due to various factors.
  • Example: Temperature variation: Dras (Ladakh) can be -45°C in winter, while Thiruvananthapuram might be 22°C. Jaisalmer (Rajasthan) can touch 50°C in summer.
  • Example: Precipitation variation: Mawsynram/Cherrapunji (>1000 cm annual rainfall) vs. Western Rajasthan (<10 cm). Most of India gets rain June-Sept, but Tamil Nadu coast gets significant rain during Oct-Nov.

2. Factors Determining India's Climate

These factors operate at different scales (global, regional, local) and interact complexly.

• A. Factors related to Location and Relief:

  • Latitude: The Tropic of Cancer (23.5° N) passes through the middle, dividing India into tropical (south) and sub-tropical (north) zones. Southern parts experience higher temperatures and less annual range compared to the north.
  • The Himalayan Mountains: Act as a crucial climatic divide.
    • Protect India from frigid cold Siberian air masses in winter.
    • Trap the monsoon winds, forcing them to shed moisture within the subcontinent.
  • Distribution of Land and Water: India is a peninsula surrounded by water bodies (Arabian Sea, Bay of Bengal, Indian Ocean). Land heats up and cools down faster than water. This differential heating creates different pressure zones, driving the monsoon winds.
  • Distance from the Sea: Coastal areas have a moderating influence (maritime climate - lower temperature range), while interior areas experience extremes (continental climate - higher temperature range).
  • Altitude: Temperature decreases with increasing height (normal lapse rate approx. 6.5°C per 1000m). Places in mountains are cooler than places on the plains.
  • Relief: Physiography plays a vital role. Windward sides of mountains (e.g., Western Ghats) receive heavy rainfall, while leeward sides remain drier (rain-shadow effect).

• B. Factors related to Air Pressure and Winds (Upper Air Circulation):

  • Surface Pressure and Winds: In winter, high pressure develops over North India (land cooler than sea), leading to offshore winds. In summer, intense low pressure (thermal low) forms over NW India (land hotter than sea), attracting onshore Southwest Monsoon winds.
  • Jet Stream and Upper Air Circulation:
    • Sub-Tropical Westerly Jet Stream (STWJ): Blows south of the Himalayas during winter across North India. Responsible for bringing Western Disturbances. Shifts north of the Himalayas during summer.
    • Tropical Easterly Jet Stream (TEJ): Develops during summer over peninsular India (approx. 14°N). Believed to play a significant role in the burst and intensity of the Southwest Monsoon.
  • Western Cyclonic Disturbances (WDs) and Tropical Cyclones:
    • WDs: Originate over the Mediterranean Sea, travel eastward under the influence of the Westerly Jet Stream. Cause light winter rainfall in North and Northwestern India (crucial for Rabi crops like wheat) and snowfall in the Himalayas.
    • Tropical Cyclones: Originate over the Bay of Bengal and Arabian Sea, mainly during the post-monsoon (Oct-Nov) and pre-monsoon periods. Cause heavy rain, strong winds, and storm surges in coastal areas (East coast more vulnerable).
  • Inter Tropical Convergence Zone (ITCZ): A low-pressure belt near the equator where trade winds converge. Its position shifts north and south with the apparent movement of the sun. During summer, it shifts over the Ganga plain, forming the 'monsoon trough,' which is fundamental to the monsoon rainfall pattern.

3. The Indian Monsoon

• Mechanism: Complex phenomenon involving multiple factors:

  • Differential heating and cooling of land and water.
  • Shift in the position of ITCZ.
  • High pressure area east of Madagascar (Mascarene High).
  • Intense heating of the Tibetan Plateau during summer, strengthening the vertical air movement and low pressure.
  • Movement of the Westerly Jet Stream north of the Himalayas and the presence of the Tropical Easterly Jet Stream.
  • Southern Oscillation (SO) & El Niño:
    • SO: A see-saw pattern of atmospheric pressure between the Eastern Pacific (around Tahiti) and the Indian Ocean (around Darwin, Australia).
    • El Niño: Appearance of warm ocean currents off the coast of Peru (Eastern Pacific) every few years. Reverses normal conditions. Often associated with weaker monsoons in India.
    • La Niña: Opposite of El Niño (unusually cold ocean temperatures in Eastern Pacific). Often associated with stronger monsoons in India.
    • ENSO: Combined phenomenon of El Niño and Southern Oscillation.

• Onset and Advance:

  • Generally arrives at the southern tip (Kerala coast) around 1st June.
  • Progressively advances northwards, covering the country by mid-July.
  • Splits into two branches:
    • Arabian Sea Branch: Strikes Western Ghats (heavy rain), moves north along the coast, enters Gujarat/Rajasthan, and merges with the Bay of Bengal branch over the Ganga plains.
    • Bay of Bengal Branch: Strikes Myanmar coast and deflects towards India, enters West Bengal/Bangladesh, moves up the Ganga plains, influenced by Himalayas and thermal low in NW India. Also causes heavy rain in NE India (Mawsynram).

• Break in the Monsoon: Periods of dry spells during the rainy season. Associated with the movement/position of the monsoon trough. If the trough lies along the Himalayas, plains get less rain; if it shifts south, plains get good rain.

• Retreat/Withdrawal:

  • Begins from NW India by early September.
  • Withdraws progressively southwards.
  • Complete withdrawal from the peninsula by early December.
  • Associated with clear skies and a rise in temperature ('October Heat').

4. The Rhythm of Seasons (Based on Monsoon Cycle)

• A. The Cold Weather Season (Winter):

  • Duration: Mid-November to February.
  • Conditions: Clear sky, pleasant weather, low temperatures, low humidity, feeble high pressure over North India. Temp decreases from south to north.
  • Precipitation: Western Disturbances cause light rain in plains and snowfall in Himalayas. Some winter rain occurs on the Tamil Nadu coast due to retreating NE monsoon winds picking moisture over Bay of Bengal.
  • Winds: Generally offshore (land to sea), part of NE Trade winds.

• B. The Hot Weather Season (Summer):

  • Duration: March to May.
  • Conditions: Apparent northward movement of the sun leads to rising temperatures and falling air pressure across India. Intense heating, especially in NW India.
  • Key Features:
    • Loo: Strong, gusty, hot, dry winds blowing during the day over North and NW India.
    • Dust storms common in North India in May.
    • Pre-monsoon Showers: Localized thunderstorms towards the end of summer.
      • Mango Shower: Kerala and Karnataka, helps in early ripening of mangoes.
      • Blossom Shower: Kerala and nearby areas, helps coffee flowers blossom.
      • Nor'westers (Kalbaisakhi): Thunderstorms in West Bengal and Assam. Destructive but bring needed rain for tea, jute, rice. ('Kal' - calamity, 'Baisakhi' - month of Baisakh).
      • Bardoli Chheerha: Local name in Assam.

• C. The Advancing Southwest Monsoon Season (Rainy Season):

  • Duration: June to September.
  • Conditions: Arrival of SW Monsoon winds, leading to widespread rainfall. Temperature drops, humidity increases.
  • Characteristics: Rainfall is often in spells ('burst' of monsoon), interspersed with 'breaks'. Governed by tropical depressions forming in Bay of Bengal and moving inland. Orographic rainfall is significant (Western Ghats, NE hills). Rainfall decreases from east to west in the Northern Plains.

• D. The Retreating Monsoon Season (Transition/Autumn):

  • Duration: October to November.
  • Conditions: Apparent southward movement of the sun. Monsoon trough weakens and shifts southwards. Gradual replacement of moist SW winds with drier NE winds.
  • Key Features:
    • Clear skies, rise in temperature ('October Heat' - due to high temp and humidity as land is still moist).
    • Low-pressure conditions shift from NW India to the Bay of Bengal by early November.
    • This shift is associated with the occurrence of tropical cyclones over the Bay of Bengal, which strike the eastern coast (esp. Tamil Nadu, Andhra Pradesh, Odisha), causing heavy rain and damage.
    • Bulk of rainfall for the Coromandel Coast (Tamil Nadu) occurs during this season from the NE Monsoon winds.

5. Distribution of Rainfall

• High Rainfall Areas (>200 cm): Western slopes of Western Ghats, Northeastern India (esp. Khasi-Jaintia hills - Mawsynram).
• Medium Rainfall Areas (100-200 cm): Eastern slopes of Western Ghats, Ganga plains (decreasing westwards), East India.
• Low Rainfall Areas (50-100 cm): Parts of Deccan plateau (rain shadow), Punjab, Haryana, parts of Gujarat, interior peninsula.
• Very Low Rainfall Areas (<50 cm): Western Rajasthan, adjoining Gujarat, Haryana, Punjab, Ladakh region, leeward side of Western Ghats.
• Variability: Rainfall is highly variable year to year and region to region. Areas with low rainfall generally have higher variability, making them drought-prone (e.g., Rajasthan, Gujarat). High rainfall areas tend to have lower variability but can suffer floods.

6. Climatic Regions of India (Koeppen's Classification - Brief Overview)

• Koeppen used temperature and precipitation (monthly and annual averages) to classify climates. He used letter codes.
• Major Types in India:
  • Amw: Monsoon with short dry winter season (West coast south of Goa).
  • As: Monsoon with dry summer season (Coromandel coast - Tamil Nadu).
  • Aw: Tropical Savanna type (Most of Peninsular plateau, south of Tropic of Cancer).
  • BShw: Semi-arid Steppe climate (NW Gujarat, parts of Rajasthan, rain shadow areas of W. Ghats).
  • BWhw: Hot Desert type (Extreme western Rajasthan).
  • Cwg: Monsoon type with dry winters (Ganga plain, eastern Rajasthan, Assam, Malwa plateau).
  • Dfc: Cold Humid winters with short summer (Arunachal Pradesh).
  • E: Polar type (Higher reaches of Himalayas - Jammu & Kashmir, Himachal Pradesh, Uttarakhand).

7. Monsoon and the Economic Life in India

• Monsoon acts as a unifying hydro-meteorological element.
• Agriculture: Indian agriculture is heavily dependent on the monsoon ('gamble in the monsoons'). Cropping patterns (Kharif season) are tied to monsoon rains.
• Water Resources: Replenishes rivers, lakes, groundwater – vital for drinking water, irrigation, hydroelectric power.
• Economy: Affects overall economy through agriculture, power generation, and related industries.
• Negative Impacts: Variability leads to floods (excess rain) and droughts (deficient rain), causing immense hardship and economic loss.

8. Global Warming and Climate Change

• Potential impacts on India's climate: Increased frequency/intensity of extreme weather events (heat waves, heavy rainfall, cyclones), changes in monsoon patterns, sea-level rise affecting coastal areas, melting of Himalayan glaciers impacting water availability in North Indian rivers.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter for your practice:

1. Which of the following factors is primarily responsible for the winter rainfall in North-Western India?
   (a) Southwest Monsoon
   (b) Retreating Monsoon
   (c) Western Disturbances
   (d) Tropical Cyclones

2. The term 'Mango Shower' is associated with which of the following?
   (a) Winter rainfall in Tamil Nadu
   (b) Pre-monsoon rainfall in Kerala and Karnataka
   (c) The burst of monsoon on the West Coast
   (d) Cyclonic rainfall on the East Coast

3. The Inter Tropical Convergence Zone (ITCZ) normally occurs near:
   (a) The Tropic of Cancer
   (b) The Equator
   (c) The Tropic of Capricorn
   (d) The Arctic Circle

4. Which part of India receives significant rainfall during the Retreating Monsoon season (October-November)?
   (a) Western Ghats
   (b) Ganga Plains
   (c) Coromandel Coast (Tamil Nadu Coast)
   (d) Northeastern States

5. The 'Loo' is a characteristic local wind experienced during which season in North India?
   (a) Cold Weather Season (Winter)
   (b) Hot Weather Season (Summer)
   (c) Advancing Monsoon Season (Rainy)
   (d) Retreating Monsoon Season (Autumn)

6. According to Koeppen's climatic classification, the 'As' type (Monsoon with dry summer) is found predominantly in which region of India?
   (a) West Coast south of Goa
   (b) Extreme Western Rajasthan
   (c) Coromandel Coast
   (d) Ganga Plains

7. The phenomenon often associated with weaker monsoon rainfall in India is:
   (a) La Niña
   (b) Western Disturbances
   (c) El Niño
   (d) Nor'westers

8. Which branch of the Southwest Monsoon causes heavy rainfall along the Western Ghats?
   (a) Bay of Bengal Branch
   (b) Arabian Sea Branch
   (c) Retreating Monsoon Branch
   (d) North-East Monsoon Branch

9. What is the primary reason for the moderating influence on the climate of Peninsular India compared to North India?
   (a) Presence of the Himalayas
   (b) Higher altitude
   (c) Influence of the surrounding oceans
   (d) Dense forest cover

10. 'October Heat' is characterized by:
    (a) Low temperature and high humidity
    (b) High temperature and low humidity
    (c) Low temperature and low humidity
    (d) High temperature and high humidity during clear skies

Answer Key:

1. (c)
2. (b)
3. (b)
4. (c)
5. (b)
6. (c)
7. (c)
8. (b)
9. (c)
10. (d)

Make sure you revise these notes thoroughly. Understand the concepts, especially the mechanism of the monsoon and the role of various factors. Relate the climatic features to the different seasons and regions of India. Good luck with your preparation!