Effects of rising seas and geomorphological changes in the islands of northern Bay of Bengal

Abstract

The geomorphology of the coastal islands of the northern Bay of Bengal is complex and dynamic in nature. During contemporary times, the geomorphology of coastal islands has been severely influenced by rising sea levels, imposing environmental stress on natural systems. Coastal island progradation and landscape loss scenarios exhibit complex behavior and are influenced by natural processes of fluvial and marine systems. Landscape geomorphic features continuously transform one into another by the natural causal mechanisms and response along with ethnographic interventions at the major islands of the Meghna estuary, which largely impacted ecosystem services, food security, and livelihood patterns of the coastal community. This paper provides historical geomorphological change statistics, the stage of development or evolution of coastal islands, dynamics progradation scenarios, landscape net loss or gain, rate of hereinafter sea-level rise, coastal island stability, impacts of sea level rise on the coastal island geomorphology, and landscape ecology. The geomorphological change of coastal islands have been assessed from ancient cartographic maps (i.e. Rennell's Map in 1776, Tassin's Map in 1840, and Topographic Survey Map in 1943) and remotely sensed satellite imagery of Landsat mission (1972–2021) by using advance RS and GIS tools via overlay analysis techniques. Using time series tidal gauge water level data (1993–2022), the present study analyzes historical trends in sea level rise and assesses its impacts on coastal ecosystems. The study finding demonstrated that coastal islands geomorphology of the northern Bay of Bengal continuously change by fluvial and marine process. Among the coastal island in the study area, the largest island Bhola was displayed noticeable erosion 192.96 km2 with an annual rate of erosion 2.47 km2/yr during the time span between 1943 and 2021. In the northern Bay of Bengal, the results from tidal gauge water level analysis revealed that the yearly maximum sea level rise rate was 9.7 mm/yr, with a strong positive correlation (R2 = 0.30), at a 95% confidence level. The study outcome helps in coastal risk assessment, mitigation strategies, development planning, and coastal resources management.