India’s climate is controlled by a number of factors which can be broadly divided into two groups —
- factors related to location and relief, and
- factors related to air pressure and winds.
Factors related to Location and Relief
- Tropic of Cancer passes through the central part of India in east-west direction. Thus, northern part of the India lies in sub-tropical and temperate zone and the part lying south of the Tropic of Cancer falls in the tropical zone.
- The tropical zone being nearer to the equator, experiences high temperatures throughout the year with small daily and annual range.
- The Himalayan Mountains in the north along with its extensions act as an effective climatic divide.
- The mountain chain provides an invincible shield to protect the subcontinent from the cold northern winds. These cold and chilly winds originate near the Arctic circle and blow across central and eastern Asia.
- The Himalayas also trap the monsoon winds, forcing them to shed their moisture within the subcontinent.
- As compared to the landmass, water heats up or cools down slowly. This differential heating of land and sea creates different air pressure zones in different seasons in and around the Indian subcontinent.
- – Difference in air pressure causes reversal in the direction of monsoon winds.
- Distance from the Sea -With a long coastline, large coastal areas have an equable climate. Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate.
- Temperature decreases with height. Due to thin air, places in the mountains are cooler than places on the plains.
- The physiography or relief of India also affects the temperature, air pressure, direction and speed of wind and the amount and distribution of rainfall.
- The windward sides of Western Ghats and Assam receive high rainfall whereas the southern plateau remains dry due to its leeward situation along the Western Ghats.
Factors Related to Air Pressure and Wind
(i) Distribution of air pressure and winds on the surface of the earth.
(ii) Upper air circulation caused by factors controlling global weather and the inflow of different air masses and jet streams.
(iii) Inflow of western cyclones generally known as disturbances during the winter season and tropical depressions during the south-west monsoon period into India, creating weather conditions favourable to rainfall.
The mechanism of these three factors can be understood with reference to winter and summer seasons of the year separately.