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The effects of global warming and climate change have begun to appear partially in the 20th century although it had begun towards the end of the 18th century or in the early 19th century. The terrible consequences of this change will be felt in the 21st century with the complete disappearance of thousands of cities and suburbs under seawater. In the abyss of the sea, not only the different infrastructures will disappear but also various civilizations, cultures and traditions will be lost forever. The main consequences of climate change are rise in sea level, salinity intrusion, coastal flooding and other natural disasters like cyclones. 

According to the draft report of Bangladesh Delta Plan 2100, owing to the deltaic formation of the country, the configuration of the rivers and climate change, low elevation, high population density and inadequate infrastructure Bangladesh has been ranked as the 5th most vulnerable country in the world in terms of risks from natural hazards. Tidal surge, salinity intrusion, flooding, river erosion and cyclones are regular features of the country. These features are posing continuous challenges to the food security of the country and livelihood of the rural population. The growing risk from the rise in sea level threatens to engulf a considerable area across the coastal belts that could displace millions of people by making them climate refugees. Already rise in sea level and drying up of upstream freshwater flows in the rivers in the southwest due to withdrawal of water of international rivers by India are hindering supplies for agriculture.

As per report of the Environmental Justice Foundation (EJF) the process of salinization has been intensified due to rise in sea levels in the coastal areas and diversion of water from upper riparian country. Due to pollution of drinking water with salt, around 33 million of individuals have become vulnerable to health problems such as pre-eclampsia during pregnancy, acute respiratory infections and different skin diseases. Agriculture, the crucial part of Bangladesh's economy has also been seriously affected and crops got destroyed by increasing salinity resulting into soil degradation. Many areas have already suffered substantial declines in yields and as a result significant reduction in the price of crops have taken place.

According to the Climate Smart Agriculture Investment Plan (CSAIP), around two-thirds of Bangladesh has been at an elevation of less than 5 metres, and that's why it is highly likely to be exposed to rising sea levels particularly in the southern region. Adverse effects of rising sea level and salinization are already being observed across the southwestern coastal areas. According to the report of the Department of Environment, Ministry of Environment and Forests, overall trend of sea-level rise in this zone was 6–21 mm per year in the last 30 years. Scientists estimated that the rise in the level of Bay of Bengal will be between 0.2-1.0 m for low to high emission scenarios by the year 2100. Food Planning and Monitoring Unit (FPMU) stated that the total amount of salinity-affected land in Bangladesh was 83.3 Mha in 1973 which has increased to 102 Mha in 2000 and 105.6 Mha in 2009. The salinity-affected land is increasing over time. A mean increase of 26% in salinity by 2050, with an increase of over 55% in most of the affected areas have been projected. It is a matter of concern that rising in sea level may reduce 24pc cropland by 2045. The increasing saline area will cause scarcity of freshwater, waterlogging and loss in agricultural production. This will have consequences for coastal settlements due to loss of livelihoods as well as for coastal economies, cultures and ecosystems.

The intensity of cyclonic storm surges and coastal inundation induced by depth and extent of storm surge are likely to increase with changing climate through rising sea level and temperature of the sea surface. The coastal zone of the country is currently one of the most disaster-prone areas of the world. The historical reports of Joint Typhoon Warning Center (JTWC) 1970-2017, reflects that maximum cyclones generated in the North Indian Ocean cross the Bay of Bengal by hitting the coastal areas of Bangladesh and among these cyclones around 73 cyclones made its landfall in the coastal areas of Bangladesh from 1960-2017.

According to a report of Institute of Water Modeling (IWM) of Bangladesh, across the coastal zone tidal amplitude ranges from approximately 1.5 m in the west to over 4 m in the east and up to 8 m at spring tide near Sandwip. The tidal amplitude is generally higher in the southeast coastal region than the southwest coastal region. In the draft report of Bangladesh Delta Plan 2100, it is clearly stated that the overall trend of Sea Level Rise (SLR) in the coastal zone is 6-20 mm/year and this trend is much higher in the Chattogram coastal plain area than the Ganges and the Meghna subzones. This uprising water level trend forms possibilities of increased intensity and extent of coastal flooding.

Three years ago, in 2017, the US space agency NASA reported that over the next century, melting glaciers could push the sea level up by 14.01 cm in Chattogram region and as a result, Bangladesh's port city Chattogram will be submerged in the next 100 years along with around 292 other mega port cities. Besides, Chattogram is highly vulnerable to flooding from tidal surges, the North Indian Ocean tropical cyclones and monsoonal rains. Sea level rise and rapid coastal erosion are set to exacerbate these existing problems. Chattogram is marked as High-risk Inundation Area for cyclone-induced storm surge by 2050 in extreme climate change scenario. The coastline of Bangladesh can be divided into three main zones - the west, central and east coastal zones. The southeast coastal region of Bangladesh is more vulnerable than the southwest region due to climate change and sea level rise and some other reasons:

This area is directly exposed to vulnerable cyclone and storm surges. The west and central coasts of Bangladesh are part of the Ganges-Brahmaputra-Meghna delta system, whereas the east coast is non-deltaic. In the west, the world's largest mangrove forest the Sundarbans dominates the coastal fringe. The Sundarbans also control the interaction of inland non-mangrove areas with the sea. The Sundarbans has shielded the southwest coastal zone from the ferocity number of cyclones like Sidr, Amphan and had been saving the coastal region repeatedly from the adverse impact of different natural disasters. The Sundarbans with its thick mangrove forest acts as a biological protective shield which not only just helps reduce wind speed drastically when the storm moves through the delta but also helps to break the waves, and the surge triggered. The Sundarbans has always been like a saviour of Bangladesh by protecting this country especially the southwest coastal region from the onslaught of cyclones and tidal surges. 

A problem that is not seen in the other three areas is flash floods from the hills immediately to the east: the steep gradients, usual tendency of hills to generate intense rainfall, rapid increases in discharge, which the rivers and other drainage channels across the flat coastal plain cannot convey safely.


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