NCERT Class 9 • Contemporary India I • Chapter "Climate" | NCERT Class 11 • India Physical Environment • Chapter "Climate"

Climatic Controls and Factors

Weather is the state of the atmosphere at a place at one moment; climate is the average of weather over a long period, usually thirty years or more. India's climate is described as tropical monsoon type, and six major controls together decide how hot, cold or wet any part of the country will be.

The Six Controls of Climate

• Latitude — the Tropic of Cancer passes through the middle of India, so the south is tropical and the north has a more continental character.
• Altitude — temperature falls with height, which is why hill stations stay cool while the plains below are hot.
• Pressure and winds — the seasonal reversal of pressure over land and sea drives the monsoon.
• Distance from the sea — coastal places like Mumbai have a small annual range of temperature; interior places like Nagpur have a large one.
• Relief — the Himalaya blocks cold Central Asian winds, and the Western Ghats force moist winds to rise and give rain.
• Ocean currents — they affect the temperature and moisture of the winds blowing over the coast.

Factors Behind India's Climate

• The Himalaya acts as a climatic divide, keeping India warmer in winter than places at the same latitude elsewhere.
• The jet stream in the upper air steers weather; the westerly jet in winter and the easterly jet in summer both matter.
• Western disturbances coming from the Mediterranean bring winter rain to the north-west.
• El Nino conditions in the Pacific are linked with weak monsoon years in India.
• The Tibetan plateau heats up strongly in summer and helps set up the monsoon circulation.
• The Thar desert heats up quickly and deepens the summer low pressure over the north-west.
• The long coastline and the peninsular shape expose three sides of India to the sea, which keeps the coasts mild through the year.

Continentality — the tendency of inland places to have very hot summers and very cold winters.