Delta under pressure: A holistic assessment of morphodynamic change in the Indian Sundarbans from 1972 to 2025

The Indian Sundarban Delta (ISD), located at the confluence of the Ganga-Brahmaputra-Meghna river system along India's eastern coast, is among the world's most geomorphologically dynamic and environmentally vulnerable deltaic systems. Over the past five decades, the region has undergone substantial morphodynamic changes driven by natural forces such as relative sea-level rise, wave action, and sediment flux, as well as anthropogenic factors like upstream water regulation via dams and barrages. This study examines the long-term evolution of shoreline and island morphology across the ISD from 1972 to 2025 using multi-temporal Landsat datasets under consistent tidal conditions. Shorelines were manually digitized and analyzed using the Digital Shoreline Analysis System (DSAS) in ArcGIS. A total of 45,356 transects were generated at 50 m intervals across eight coastal zones, covering approximately 2980 km of shoreline. Shoreline dynamics were assessed using Net Shoreline Movement (NSM) and End Point Rate (EPR), which ranged from -3286 m to +4510 m and -62.97 m/year to +125.75 m/year, respectively. Additionally, Areal analysis of 92 tidal islands revealed a net land loss of 72 km², driven by 256.31 km² of erosion and partly balanced by 183.88 km² of accretion. Ocean-facing island margins displayed the highest morphodynamic instability and erosion rates. Notably, the emergence of several new sand patches suggests localized deposition that could develop into stable landforms under favorable conditions. These spatial-temporal trends are closely linked to sea-level rise, upstream sediment retention, swell wave dominance, and increased cyclone frequency, underscoring the need for integrated coastal management.