The average annual rainfall varies from a maximum of 5,690 mm in the northeast of the country to minimum of 1,110 mm in the west. The groundwater, however, provides adequate storage to compensate for annual variations in rainfall and stream flow. The average annual discharge from the three major rivers - a total of 35,000 cusec- is second only to the Amazon. The carry billions of tons of sediment load every year.
As it is situated in the tropic, the country is prone to cyclones associated with tidal surges, especially in the pre-monsoon and post-monsoon months. Because of high density of population in the flat deltaic coastal region, the loss of human lives in such cyclones has at time been very heavy.
The country experiences a hot summer of high humidity from late March to late June, a somewhat cooler but still a hot and humid monsoon from late June through October and a cool dry winter from November to the end of February. Day temperature ranges from 7 to 12 degree centigrade in the cool months and in the other months it varies between 23 to 30 degree centigrade.