CH 4 CLIMATE

• Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than thirty years)
• Weather refers to the state of the atmosphere over an area at any point in time
• Elements of weather and climate: temperature, atmospheric pressure, wind, humidity and precipitation
• Year divided into seasons based on monthly atmospheric conditions: Winter, Summer, Rainy Seasons
• Factors influencing climate:

  • Latitude: air temperature decreases from the equator towards the poles
  • Altitude: temperature decreases with higher altitude, hills are cooler during summer
  • Pressure and wind system: influences temperature and rainfall pattern based on latitude and altitude
  • Distance from the sea: sea moderates climate, extreme weather conditions with increased distance known as continentality
  • Ocean currents: affect coastal climate, warm or cold currents impact temperature
• • Relief features: high mountains act as barriers to winds, cause precipitation if in path of rain-bearing winds
• India's climate factors:

  • Latitude: Tropic of Cancer passes through, tropical and subtropical climates
  • Altitude: mountains to the north, milder winters compared to central Asia
  • Pressure and winds: governed by pressure, surface winds, upper air circulation, cyclonic disturbances, and monsoons
• Indian Monsoon:

  • Influenced by monsoon winds
  • Seasonal reversal of wind system known as monsoon
  • Experienced between 20° N and 20° S
  • Differential heating and cooling of land and water create low pressure on landmass
  • Shift of Inter-Tropical Convergence Zone (ITCZ) in summer over Ganga plain
  • High-pressure area east of Madagascar affects Indian Monsoon
  • Tibetan plateau heating results in low pressure, westerly and easterly jet streams impact monsoon
  • Changes in pressure conditions over southern oceans affect monsoons
  • Southern Oscillation (SO) affects climate of tropics and subtropics
• Onset and Withdrawal of Monsoon:

  • Duration: 100-120 days from early June to mid-September
  • Arrival: southern tip of Indian peninsula by 1st week of June, branches into Arabian Sea and Bay of Bengal
  • Withdrawal: begins in northwestern states by early September, complete withdrawal by early December
• Seasons in India:

  • Cold Weather Season (Winter): mid-November to February, coldest in December and January, clear sky, low temperatures, important for 'rabi' crops
  • Hot Weather Season (Summer): March to May, loo winds, pre-monsoon showers, early ripening of mangoes
  • Advancing Monsoon (Rainy Season): south-east trade winds, southwest monsoon, monsoon trough, breaks in rainfall, tropical depressions
  • Retreating/Post Monsoons (Transition Season): October-November, clear skies, rise in temperature, 'October heat'
• Distribution of Rainfall in India:

  • Western coast and northeastern India receive over 400 cm annually
  • Rainfall less than 60 cm in western Rajasthan, parts of Gujarat, Haryana, Punjab
  • Low rainfall in interior Deccan plateau and east of Sahyadris
  • Snowfall restricted to Himalayan region
  • Annual rainfall highly variable
• Monsoon as a Unifying Bond:

  • Monsoon influences rhythmic cycle of seasons
  • Uncertainties of rain and uneven distribution typical
  • Monsoon winds bind India by providing water for agricultural activities