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Floods in Bangladesh
Bangladesh is prone to flooding due to being situated on the Ganges Delta and the many distributaries flowing into the Bay of Bengal. Coastal flooding, combined with the bursting of river banks is common, and severely affects the landscape and society of Bangladesh. 75% of Bangladesh is less than 10m above sea level and 80% is floodplain, therefore rendering the nation very much at risk of periodic widespread damage, despite its development. Whilst more permanent defences, strengthened with reinforced concrete, are being built, many embankments are composed purely of soil and turf and made by local farmers. Flooding normally occurs during the monsoon season from June to September. The convectional rainfall of the monsoon is added to by relief rainfall caused by the Himalayas. Meltwater from the Himalayas is also a significant input.
Each year in Bangladesh about 26,000 km2 (around 18% of the country) is flooded, killing over 5,000 people and destroying more than seven million homes. During severe floods the affected area may exceed 75% of the country, as was seen in 1998. This volume is 95% of the total annual inflow. By comparison, only about 187,000 million m3, of streamflow is generated by rainfall inside the country during the same period. The floods have caused devastation in Bangladesh throughout history, especially during the years 1966, 1987, 1988 and 1998. The 2007 South Asian floods also affected a large portion of Bangladesh.
==Benefits of flooding==
Small scale flooding in Bangladesh is required to sustain the agricultural industry, as sediment deposited by floodwaters fertilises fields. The water is required to grow rice, so natural flooding replaces the requirement of artificial irrigation, which is time consuming and costly to build. Salt deposited on fields from high rates of evaporation is removed during floods, preventing the land from becoming infertile. The benefits of flooding are clear in El Niño years when the monsoon is interrupted. As El Niño becomes increasingly frequent, and flood events appear to become more extreme, the previously reliable monsoon may be succeeded by years of drought or devastating floods.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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