Ecosystem and natural disasters

Sea-level rise is being considered one of the adverse impacts of global climate change but is not being discussed extensively. It could be due to lack of sufficient information regarding impacts of a sea-level rise. Dr Mahabub Hossain can be a guide in this regard. In a seminal paper, he argues that sea-level rise could hit rural livelihoods hard.
Bangladesh now supports about 156.6 million (2013) people within a land area of 147,570 square kilometres. But the population is still growing at 1.4 per cent adding two million new mouths to be fed every year. The fact remains that the country is situated on deltas of large rivers flowing from the Himalayas. The Ganges unites with the Jamuna (the main channel of the Brahmaputra) and later joins the Meghna to eventually be emptied in the Bay of Bengal. The country is sloping gently from the north to the south, meeting the Bay of Bengal in the southern end. The three major rivers and their numerous tributaries carry water from the catchments of the Himalayas and flood a third of the country in normal years. When they rise at the same time and the drainage to the sea is impeded by high tide in the sea, the country suffers disastrous floods with inundation of over 50 per cent of the land area.
Bangladesh runs parallel to the Bay of Bengal forming 710 km long coastline. The coastal zone covers 19 of the 64 districts of which 12 districts meet the sea or lower estuary directly. The number of upazilas (sub-districts) that are directly exposed to the coast is 48. Another 99 upazilas (out of 508) are located behind the exposed coast (interior coast) are subjected to tidal fluctuations and are affected by saline water intrusion. The coastal zone covers 47,000 square km  area, about 32 per cent of total landmass of the country. Twenty-eight per cent of the total population lives in the coastal zone. The average population density in the coastal zone is currently 890, about 12 per cent lower than the average for the country as a whole. The population density is, however, only about half in the exposed zone (570 per square km) compared to the interior zone (1200 square km). A one-metre rise in sea level will inundate about 17.5 per cent of the landmass mostly in the central and western coast ( 9 districts in Barisal and Khulna regions).
The Bangladesh coast is often devastated by severe cyclonic storms and tidal surges that take heavy toll on human lives, infrastructure and livelihoods. The devastation caused by three major cyclones occurred in 1970, 1985, 1991 and 2007 are still vivid in the memory of the present generation.  The November 1970 cyclone with a tidal surge of over nine metres caused death of 500,000 plus people.  The neglect of relief and rehabilitation in its aftermath by the central government is considered a major factor behind the break-up of Pakistan and the independence of Bangladesh in 1971. The cyclone of April 1991 in the eastern coast caused a death toll of 139,000 people with an estimated economic loss of US$ 1.78 billion. The most recent cyclone, Sidr, which struck the south-western coast on November 15, 2007 with a wind velocity of up to 250 km per hour took a toll of 33,363 people with another 871 missing. It affected 2.06 million households and 8.96 million people and destroyed crops on about 2.5 million ha of land.
The frequency and intensity of natural disasters is projected to increase with climate change and sea-level rise. Rising sea levels will impede drainage of water southwards from the Himalaya terrain by the major rivers. This feedback effect can cause penetration of heavier floods further inland. The storm surge during cyclone may increase to over 9 metres with heavier risks, loss of human and animal lives and destruction of assets.
Bangladesh is a severe land-scarce country. A third of the rural households are landless, some of whom regularly migrate to ecologically risky areas such as unprotected coasts or newly- established islands in riverbeds and estuaries for habitation and livelihoods. Some people even live on boats and make a living on fishing and river transport. The average size of land holdings has declined from 1.47 ha in 1961 to only 0.6 ha in 2005 despite rapid rural urban migration of the population. The sea-level rise will make the situation worse. A one-metre increase in the sea level will inundate nearly 30,000 square km area. It will make an additional 15 million people landless who will become environmental refugees.
Sea-level rise will affect food and agricultural production by increasing the intensity of salinity intrusion in the dry season and the depth of flooding in the wet season from tidal fluctuations. The climate change will increase the frequency of cyclones and occasional depressions that will affect agricultural production through heavy rains and increased velocity of winds. Salinity intrusion will decrease agricultural production by degrading soils and reducing availability of fresh water. Already nearly one million ha of land in the east and the western coasts suffer from soil salinity which inhibits adoption of improved varieties of rice that has helped achieve a respectable growth in food production in other parts of Bangladesh.
    The Barisal region (the central coast) was once the food basket of the country, but it has now become a food-deficit region due to continued pressure of population on fragile land resources, and the sluggish growth in agricultural production. Sea-level rise will further aggravate the unfavourable growing conditions for most agricultural crops.
It is difficult to predict the direction of impact of sea-level rise on fisheries which is an important source of livelihood of the coastal population at present.  Inundated fields and expansion of estuaries may increase the fish habitat which may have a favourable impact on fisheries production. Many low-lying fields in the coastal belt have now been turned into fish ponds with marginal investments. Higher frequency of cyclones, intensity of tidal surge, and flooding would make inland fisheries a more risky venture in the region.
Sea-level rise may also increase the risk of health hazards by spreading communicable diseases (such as diarrhoea) due to lack of pure drinking water. Increased intrusion into the fresh water zone of saline sea water will decrease drinking water availability in the region. Due to soil salinity, use of tube wells as a source of drinking water is already rare in the region. People usually use ponds as a source of drinking water.

The writer is a Professor of Economics at Jahangirnagar University.
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