There is heavy rainfall on the western coast of India but very little in the Deccan because

There is heavy rainfall on the western coast of India but very little in the Deccan because the Deccan plateau is situated in the rain shadow of the Western Ghats. The Deccan Plateau to the east of the Western Ghats receives significantly less rainfall than the coasts. As the summer (wet) monsoons approach the West Coast of India, they rise up the western Ghats (mountains) and the air cools. This cool air is less able to hold moisture and it is released as rainfall.