Question

why does the rainfall decrease in the from the west in the Northern India

Answer 1

Mostly the bay of Bengal branch of the south west monsoon winds bring rain to northern India.Most of moisture in this wind fall in the form of rain in the high mountains of Meghalaya Assam and west Bengal.Due to these hills one branch of this winds deflects towards west and gives rain on its way as it advances.that is why the rainfall decreases in northern India while going from West.

Answer 2

the rainfall decrease because the clouds carry less moisture in the part of West.