Monsoons are the rain giver in India. India 's climate ,(temperature & rainfall) depend entirely on monsoons. India would have been arid like west Asia, as their been no monsoons. The winds would have become dry till these reached western parts (like Rajasthan). Without monsoons, there would not been dense forests in India. It would have the desert vegetation like bushes & shrubs. Monsoons are wet as these pick up moisture from Indian Ocean, but here the prevailing winds would have come from land & would have been dry . The word ‘monsoon’ refers to the seasonal reversal in the wind direction during a year. The monsoon winds are confined to the tropical area lying between 20ON to 20OS latitudes. The mechanism of monsoons or the phenomena of the seasonal reversal in wind direction is related to the following fact:
1. The differential heating and cooling of land and water.
2. The shift of the position of Inter Tropical Convergence Zone (ITCZ) in summer over the Ganga plain.
3. The presence of high pressure area, east of Madagascar over the Indian Ocean. The intensity and position of this high pressure area affects the Indian monsoon.
4. The Tibetan plateaus gets intensely heated during summer resulting into strong vertical air currents and the information of low pressure over the plateau.
5. The movement of the westerly Jet Stream to the north of the Himalayas and the presence of the tropical easterly Jet Stream over the Indian Peninsula during summer.
The meteorologists have found out a seesaw kind of relationship between the meteorological changes going on over the Pacific and the Indian Ocean. Whenever there is high pressure in the subtropical region of the Pacific Ocean in the northern hemisphere, the pressure in the south of Indian Ocean tends to be low and vice-versa. This is known as the ‘Southern Oscillation’ or SO which causes the shifting of winds across the equator in different directions. Besides the above facts, some other events such as ElNino, ENSO etc. are also connected to the mechanism of monsoons.