Rainfall decreases from east to west in Northern India because:

i. When the Bay of Bengal Branch of south west monsoon is obstructed by the Nepal and eastern Himalayas, maximum amount of rainfall is received in West Bengal, Bihar etc.

ii. When these winds advance towards west they go on shedding moisture.

iii. In Kolkata the amount of rainfall is 105 cms.

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iv. In Delhi, it is only 59 cms.

v. Further it goes on decreasing and in Ambala it is less than 40 cms.