The rainfall decreases from east to west in northern India because of the following reason:
The inflow of the south-west monsoon into India is such that the windward side of the Western Ghats receives very heavy rainfall, more than 250 cm. The rain shadow region receives scanty rainfall and the moisture laden clouds shed the maximum rainfall of this season in the north-eastern part of the country. Thus, Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world. Rainfall in the Ganga valley decreases from the east to the west. Hence, Rajasthan and parts of Gujarat which are on the western get scanty rainfall.