Based on precipitation or amount of rain that falls on the earth’s surface in a year earth has been divided into the following regions:
a) Arid region: That region where annual rainfall is less than 250 mm. Crop production is dependent on supplemental water supply through irrigation in these areas.
b) Semi-arid region: Those areas where annual rainfall is about 250-500mm and crop production of these areas requires either farming practices that conserve water or needs additional irrigation when there is uneven and erratic rainfall.
c) Semi-humid region: Those areas where annual rainfall is about 750-1000mm and these areas are allowed the cultivation of different types of crops.
d) High humid region: Areas that have annual rainfall of more than 1000 mm and these areas are suitable for cultivation of water requiring crops like rice, jute etc.