The eastern Chattogram coastal plain, among three geographically distinct regions of Bangladesh's coast, is the most vulnerable to relentless sea level rise (SLR), a new study found.
This finding contradicts those of earlier studies, which found the other two regions to be more vulnerable.
Due to the strategic importance in trade, industry, and tourism, the Chattogram and Cox's Bazar regions are considered commercially important for Bangladesh.
According to the study, titled "Estimating vertical land motion-adjusted sea level rise in a data sparse and vulnerable coastal region", the SLR rates vary significantly among the three coastal zones — higher in the eastern flat plain of Chattogram and Cox's Bazar (4.73mm/year), moderate in the western Ganges tidal plain of Sundarbans (3.66mm/year), and lowest in the central Meghna estuarine floodplain of Bhola, Noakhali, Lakshmipur, Chandpur, and parts of Barisal (2.4mm/year).
The global mean sea level (GMSL), which is currently rising by approximately 3.3 mm/year, is not only increasing but has also shown signs of acceleration in recent decades, primarily due to anthropogenic factors, according to the Intergovernmental Panel on Climate Change (IPCC).
Bangladesh, with its low-lying topography and high population density, is one of the most vulnerable countries to GMSL rise.
Compared to the rate of increase of GMSL of 3.3mm/year, the observed Relative Sea Level Rise (RSLR) in Bangladesh is approximately 2.1mm/year higher, calculated taking into account the combined effects of rising ocean levels and local land deformation, as per the study published on 17 August.
"Sea level rise is not only caused by the glacial retreat or ice melting as a result of climate change, but also by relentless land demolition and reclamation into the sea. This is the reason why the sea level rise is most severe at Chattogram, Cox's Bazar areas, the economic heartlands of Bangladesh," Ashraf Dewan, lead researcher of the study, told Stream.
The study published in the GEOMATICS, NATURAL HAZARDS AND RISK journal was conducted by researchers Dewan (School of Earth and Planetary Sciences, Curtin University, Perth, Australia), Hardik Jain (School of Electrical Engineering, Computing and Mathematical Sciences, Curtin University), Md Alamgir Hossain (Economic Relations Division, Bangladesh government), Mohammed Sarfaraz Gani Adnan (Department of Civil and Environmental Engineering, Brunel University of London, UK) and Md Redowan Mahmud (School of Electrical Engineering, Computing and Mathematical Sciences, Curtin University).
The study, which spanned more than two years, contradicts many other earlier studies on SLR at Bangladesh's coast, which predominantly resulted in finding the western Ganges tidal plain of Sundarbans or the central Meghna estuarine floodplain as the most vulnerable regions, whereas the eastern part of the coast showed the lowest rate of rise or fall.
Those previous studies were mostly conducted by using either single or multi-station tide gauge (TG) records, which reflect relative sea level rise (RSLR) combining the ocean height changes and vertical land motion (VLM), or satellite altimetry (SA), or tidal and inland water records.
For this, inconsistencies and overestimations in SLR rates remained in different studies, as per the study.
"Think of a glass of water; if you drop one pebble there, the water level will rise. If you keep dropping one after another, the water level will rise too, and overflow eventually. This is happening in the coastal regions of Bangladesh, where unplanned constructions and urbanisation have been leading to sea level rise at a fast pace," said Dewan.
To obtain a measure of absolute sea level rise (ASLR), it is necessary to correct TG records using VLM estimates from satellite altimetry (SA), global navigation satellite systems (GNSS), and interferometric synthetic aperture radar (InSAR).
Therefore, the research group felt the necessity to combine TG records, SA, and InSAR-derived VLM data for an integrated analysis of sea level rise across coastal Bangladesh, one of the most climate-vulnerable regions in the world.
The VLM-adjusted ASLR rate, averaging 4.58mm/year, closely matched the SA-derived ASLR rate of 4.94mm/year, which validates the integrated approach used in this study.
"By capturing these spatial and temporal complexities, the study contributes to a more nuanced understanding of coastal vulnerability in Bangladesh," the study claimed.
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