Geospatial analysis of shoreline dynamics and drivers in the Sundarbans Biosphere Reserve (1990–2020): Integrating natural and anthropogenic influences for coastal resilience

The Sundarbans Biosphere Reserve (SBR), spanning India and Bangladesh, encompasses the world's largest mangrove forest and is recognized as a critical biodiversity hotspot. This study investigates shoreline dynamics in the SBR from 1990 to 2020 using multi-temporal Landsat imagery and the Digital Shoreline Analysis System (DSAS). Shoreline changes were quantified at long-term (decadal), short-term (five-year), and interannual scales using the Weighted Linear Regression Rate (WLR), End Point Rate (EPR), and Net Shoreline Movement (NSM) methods, respectively. The study area was divided into five zones based on river estuaries and administrative boundaries, comprising 13,605 transects covering approximately 1360 km of coastline. Results indicate that Zone III (Hariabhanga to Malancha estuary) experienced the most severe erosion, with 74.04 % of transects affected. Zone II recorded the highest mean erosion rate at -7.03 m/year. In contrast, Zone I exhibited the greatest accretion, with 43.03 % of transects gaining land and a mean rate of 2.68 m/year. Short-term shoreline variations were predominantly influenced by climatic events, particularly cyclones. Interannual shoreline statistics show that erosion peaked during 2015-2016, with a mean erosion rate of -91.76 m/year, whereas accretion was dominant during 2002-2003, with a mean accretion rate of 146.75 m/year. Overall, the mobility of shoreline dynamics is strongly influenced by extreme climatic events.