Floods -Extent and Causes 

Bangladesh and India are among the most flood prone nations on the whole earth. Another risky countries in Southern part of Asia are Pakistan, Nepal and Sri lanka. It should be noted that although Maldives does not experience floods as in the rest of the Southern part of Asia.
The main and fundamental reasons for floods in these countries lies in the very nature of their natural ecological systems- the monsoon, the highly sediment ed river systems, and the steep and highly erodible mountains, particularly those of the Himalayan range.

 The heavy spells of rainfall occur in association with the formation and movement of depressions or cyclonic storms, which originate in the Bay of Bengal and sometimes in the Arabian Sea. The main rainy season is form June to September for almost the whole country, when it comes under the grip of the southwest monsoon, and accounts for 80 percent or more of the annual rainfall except in the Brahmaputra region and part of the peninsula. The south-west monsoon sets in the first week of June over Kerala and then extends northward and covers the whole country by early July. Majority of the floods occur during the monsoon period and are usually associated with tropical storms or depressions, active monsoon conditions, and break monsoon situations. .  

 Bangladesh, being a low and flat country, has a number of permanent water bodies called beels and haors formed by the abandoned courses of its meandering and changing rivers. Some of the beels and haors are very large and are not fully drained. They are sufferer of water logging because they do not get drained out even during the dry months due to heavy sedimentation in drainage channels. Water logging in the dry season is not a major problem in Bangladesh but delay in drainage of flood waters makes it too late to replant crops in the vast low lying fields of the country, it affecting agricultural production.