Shoreline Dynamics in the Sundarbans Delta (1975–2022): A Multi-decadal Remote Sensing Assessment

Abstract

The Sundarbans, spanning the Ganges-Brahmaputra-Meghna (GBM) delta across India and Bangladesh, is the world's largest contiguous mangrove ecosystem, covering approximately 10,000 km². This ecologically, socio-economically, and climatically vital region is facing unprecedented threats from climate change, including sea-level rise, subsidence, and reduced sediment supply due to upstream dams and interventions.The objective of this paper is to examine the delta dynamics of the Sundarban delta, focusing on shoreline erosion, breaching, and morphological changes, while exploring their associations with climatic and anthropogenic factors. A multi-temporal Landsat data (1975-2022) of 30 m resolution were used. After radiometric and atmospheric corrections shoreline map were extracted. The changes of the shoreline is detected under the GIS environment. Our study, analysing 47 years (1975-2022) of multi-temporal Landsat imagery and GIS-based change detection indicators, reveals a net land loss of ~270 km², averaging ~5.7 km²/yr. The erosion rate peaked between 1994-2005 (~17 km²/yr) due to increased cyclone frequency and decreased sediment supply. Accretion rates have steadily declined, dropping by a factor of 0.60 km²/yr between 1975-1988 and 2015-2022.Spatial analysis indicates severe erosion on the southern and western coasts due to tidal and wave actions, with moderate accretion along eastern river mouths. The Sundarbans is shifting from a historically accreting delta to a net erosional coast, contrary to most deltas. Projected sea-level rise (0.6-1.1m by 2100) threatens to submerge large areas, causing land loss, salinity intrusion, and biodiversity decline.Urgent interventions, including sediment augmentation, mangrove restoration, and adaptive coastal zone management, are necessary to protect the Sundarbans (a UNESCO World Heritage Site and vital carbon sink) from irreversible degradation.