Explanation:

South west monsoon are the main  mechanism  through  which nearly all Indian land mass experience rainfall. It accounts for nearly 80% rainfall of whole India. Vast size of Indian continent helps in developing the thermal gradient necessary to attract the vapour laden air from  sea.  Very high and extensive mountain systems of the Himalayas in  the north, extending in an east-west direction, thus posing a formidable physical barrier between tropical and polar air masses. These barriers induce the precipitation of water  from moisture laden air. As the air climb up the Himalayas their moisture retention capacity decreases due to cooling effect and this results into high rainfall.