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Climate Change and Land Use Change in Bangladesh. An Amphibic Country under Increasing Pressure.
The people of Bangladesh and their environment will be particularly affected by the effects of climate change. As most parts of the country lie table flat just above sea-level, marine transgression is one of the main threats for the living environments and a carefully growing economy. Vast areas of this deltaic environment can be described as amphibic or semiamphibic and in case of storm or monsoon induced floodings more than 2/3 of the country are submerged.
The hydrological situation is characterized by three major river systems running through the country and tidal- marine influence from the south. Both hydrological systems interact and underlie intense variations which are partly influenced by human activities. A precarious economic situation and an increase in the country´s population forces people to further intensify their agricultural activities. Furthermore more and more people settle in highly vulnerable environments or move into one of the larger cities.
Nearly all ecosystems of Bangladesh will face serious changes due to the impact of global warming. Rising temperatures will lead to changes in precipitation patterns, river discharge, storm activities and coastal environments. More rain during the monsoon and less rain in dry seasons are predicted for the future. This sharpening climatic contrast between the seasons will have an impact on agriculture and can even lead to droughts in the northwest. In addition more intense and more frequent tropical storms are predicted for the Bay of Bengal. With 800 km coastline and vast semiamphibic regions characterising the Hinterland the country is particularly affected by a rising sea level. The coastline is supposed to move several kilometres inland. Population pressure, inadequate forms of land use and the impact of climate change will increase the vulnerability of Bangladesh within the next decades.
Over time people in rural environments have developed adaptation strategies for surviving in such a dynamic natural environment. There is a local proverb, which says: People don’t die in the floods; they die when there are no floods. Bangladesh’s rural community relies on a degree of ‘normal’ flooding to bring in moisture and fresh sediment. Drastic man made changes like the various effects of global warming and the degradation of natural ecosystems for economic reasons lead to a situation which is more and more unpredictable. Storm events, riverbank erosion, inundation and flooding will occur much faster then decades ago.
Since the end of the Pleistocene rivers have delivered a large amount of sediments down from the Himalayas constituting about 80 per cent of todays landmass. Even the dramatic Holocene sea-level rise of about 120 meters had been compensated by sedimentation processes. The mighty Ganges-Brahmaputra delta complex has developed over the last 10 000 years under mainly transgressional conditions. Extended mangrove forests along the coast compensated impacts from land and sea. The impact of storm surges on the Hinterland and the river systems where reduced, whereas the roots acted as vast sediment catchment areas. Under undisturbed ecological conditions the sediments constituting the delta complex could benefit from marine transgression. As a consequence Bangladesh would even grow.
Within the last 30 years most of the protecting mangrove fringe has been cut to give room for the construction of large shrimp farms. Apart from the loss of habitats for fauna and flora sediment material is lost by increasing abrasion and bank erosion. Flood events develop much faster and the wind speed of tropical storms is not reduced by friction