Sea levels in Bangladesh could rise twice as much as predicted

An international research recently revealed that sea levels are rising more rapidly than previously thought. According to the research conducted by Mélanie Becker at the University of La Rochelle, France, and her colleagues, the sea-level could rise by 85 to 140 cm by 2100, nearly double the previous estimates. 

Researchers from La Rochelle Université, Université des Antilles the Bangladesh University of Engineering and Technology, among others, were involved in this research. It was published in the Proceedings of the National Academy of Sciences of the United States of America on 6 January 2020. It shows that a sea-level rise of almost twice as much as previously predicted could seriously affect parts of Bangladesh and India. 

Photo: Mumit M

Among others, AKM Saiful Islam, Professor of Institute of Water and Flood Management, Bangladesh University of Engineering and Technology (BUET) was the co-author of the article. 

He told that the research was completed form 2014-2018 under a project. 

''According to the global prediction of Intergovernmental Panel on Climate Change (IPCC), the sea level rise would be 1m within 2100 century for climate change. But it's the average prediction. The situation is varied from area to area.'' said Prof AKM Saiful Islam.

Photo: Mumit M

"Bangladesh and parts of India could be hit by sea-level rise almost twice as high as previously thought due to land subsiding. The coastal people will be the main victim of the consequences. Rise of saline water, internal migration and destruction of Sundarbans are the result of such changes in sea level,'' he added.

Rising sea level due to climate change is an old concern for Bangladesh. It was predicted years ago that our country would be one of the first victims of submergence in the rapidly warming weather.

Photo: Mumit M

The latest report of the Intergovernmental Panel on Climate Change (IPCC), an intergovernmental body of the United Nations, projected that the Global Mean Sea Level will rise between 43 cm to 84 cm by 2100, relative to 1986–2005. However, as the new research found, the situation is much more dire than previously assumed. 

Their estimate is based on the Ganges-Brahmaputra-Meghna delta, which makes up about two-thirds of Bangladesh. This area is already prone to flooding, as a tenth of the delta in Bangladesh is just a metre above sea level. The new analysis found that, depending on the region of the delta, sea-level rise could reach 85 to 140 cm by 2100, nearly double the estimate by IPCC.

Photo: Mumit M

This area is also prone to flooding due to intense monsoon rainfall, rising sea levels, river flows and land subsidence. Disentangling these factors and assessing their effect is difficult. The forecasts on rising water-levels carried out in the past had mostly been highly localised. 

The most recent study used 101 gauges measuring water and sea levels across the delta. The researchers found that between 1968 and 2012, water level here increased by 3 mm/year on average, slightly more than the global mean sea level rise, which was 2 mm/year during the same period. 

A recent paper published by the Asian Development Bank (ADB) predicts that during the 2040-2059 period, Bangladesh will lose 36.49 percent of its GDP per capita/Photo: Mumit M

Investigating the reason behind this discrepancy, the researchers then estimated the contribution of land subsidence – obtained by subtracting the measurements of relative water level obtained previously from the absolute sea level.

Maximum land subsidence in the delta between 1993 and 2012 was between 1 and 7 mm/year. These values are lower than some local measurements (e.g. 1-2 cm/year in Dhaka) that have been used as a reference until now. 

Assessment of land subsidence has made the picture clearer. If subsidence continues at the same rate, and even under a greenhouse gas mitigation scenario, water-level rise in the delta could reach 85 to 140 cm by the end of the century compared to the period 1986-2005. This is twice as high as the projections provided in the latest IPCC report. The latest IPCC report had not taken land subsidence into account, which caused such a vast difference in the two reports.