A branch of Summer Monsoon from Bay of Bengal moves up the Ganges Valley, it moves westwards along the Himalayas. The lower Ganges Valley receives the rainfall first and the upper Ganges Valley later on. Kolkata has an annual rainfall of 160 cm. As the branch of monsoon moves westward, it gets drier and drier. So it gives less rainfall. Varanasi gets 104 cm. of rainfall, Delhi gets 66 cm of rainfall.