Chapter: Climate (Class 11 Geography)

• Introduction

  • Definition of Climate (weather conditions over a long period, 30+ years)
  • Definition of Weather (state of atmosphere at a specific time/place)
  • Concept of Monsoon (seasonal reversal of wind direction)
  • Spatial and temporal variations in India's climate

• Unity and Diversity in Monsoon Climate

  • Unity: Tropical monsoon type, dominance of seasonal winds, rhythmic cycle of seasons
  • Diversity:
    • Temperature extremes (Rajasthan vs. Kerala/Himalayas)
    • Precipitation extremes (Cherrapunji/Mawsynram vs. Thar Desert)

• Factors Determining India's Climate

  • Location and Relief
    • Latitudinal extent (Tropic of Cancer divides India; South = tropical, North = subtropical)
    • Himalayan barrier (blocks cold Central Asian winds, traps monsoon winds)
    • Distribution of land and water (peninsular shape creates moderating maritime influence)
  • Air Pressure and Wind System
    • Surface winds and upper-air circulation (Jet Streams)
    • Cyclonic disturbances (Western Disturbances and Tropical Cyclones)

• Mechanism of Weather in India (Seasonal Cycle)

  • Winter Season (Dec - Feb)
    • Clear skies, low temperatures, high pressure in North
    • Northeast trade winds dominate (offshore, dry)
    • Western Disturbances bring winter rain to North-West India (vital for Rabi crops)
    • Localized rainfall in Tamil Nadu coast from retreating NE trade winds
  • Summer Season (Mar - May)
    • Rising temperatures, low pressure in interior India
    • Localized convective storms: Kaalbaishakhi (West Bengal), Mango Showers (Kerala/Karnataka)
    • Loo (hot, dry, gusty winds in North/North-West India)
  • South-West Monsoon Season (Jun - Sep)
    • Sudden onset ("Monsoon Burst") due to intense low-pressure over North India
    • ITCZ (Inter Tropical Convergence Zone) shifts north (Monsoon Trough)
    • Two branches:
      • Arabian Sea Branch: Causes heavy rain on Western Ghats and North-West India
      • Bay of Bengal Branch: Causes rain in North-East India and Bengal, deflects westward along Himalayas
    • Monsoon Break: Wet spells interspersed with dry intervals
  • Retreating South-West Monsoon Season (Oct - Nov)
    • Monsoonal winds weaken and withdraw southwards
    • Clear skies, rise in temperature (October Heat)
    • Tropical cyclones form in the Bay of Bengal, hitting the eastern coast

• Distribution of Rainfall

  • High Rainfall Areas (> 200 cm): Western Ghats, North-East India, sub-Himalayan region
  • Medium Rainfall Areas (100 - 200 cm): Ganga plain, Eastern MP, parts of Odisha/Peninsular plateau
  • Low Rainfall Areas (50 - 100 cm): Western UP, Punjab, Haryana, interior Deccan plateau
  • Scanty Rainfall Areas (< 50 cm): Thar Desert, Ladakh, rain-shadow areas of Western Ghats

• Climatic Regions of India (Köppen's Scheme)

  • Am (Tropical monsoon with short dry season): West coast south of Goa
  • Aw (Tropical savanna): Most of the peninsular plateau
  • BWhw (Semi-arid steppe): Western Rajasthan and parts of Gujarat/Haryana
  • BWhw (Hot desert): Extreme western Rajasthan
  • Cwg (Monsoon type with dry winter): Ganga plain, parts of North India
  • Dfc (Cold humid winter): Arunachal Pradesh
  • ET (Tundra type): Mountainous areas of Himalayas
  • E (Polar type): Higher Himalayan ranges

• Monsoon and the Indian Economy

  • Agriculture heavily dependent on timely monsoon ("gamble on the monsoon")
  • Spatial and temporal unpredictability leads to droughts or floods
  • Hydroelectric power generation and drinking water supply depend on monsoon reservoirs
  • Economic unity fostered by the unifying pull of the monsoon system

• Global Climate Change and Extreme Events

  • El Niño and La Niña phenomena affecting Indian monsoon intensity
  • Increasing frequency of extreme weather events (unseasonal rains, droughts, cyclones)
  • Global warming impacts on Himalayan glaciers and sea-level rise