Question

why does rainfall decrease from east to west in northern indea​

Answer 1

it is because when the monsoon wind travel from south to west end when it goes in North then most of the rain falls down due to collision with him aaya and hence West region receive less rainfall

Answer 2

This is because the mountains terrains block the clouds Due to which rain is poured on that region due to which Meghalaya receives heighest rainfall throughout year whereas Rajasthan receives less rainfall