Impacts of Cyclones Fani, Bulbul and Amphan on shoreline erosion dynamics in the Sundarbans mangrove forest in India and Bangladesh.

Abstract:

The Sundarbans region shared between India (38%), and Bangladesh (62%) is one of the largest (~10,000 km²) mangrove forests in the world. It experiences about five cyclonic storms every year, two of which can be of severe category. Sundarbans has a dynamic shoreline where the rate of erosion is exceeding the rate of accretion, leading to a continuous loss of mangroves. The cumulative impact of frequent cyclones on shoreline erosion dynamics in the Sundarbans and mangrove forests, globally, is currently unknown. This study estimates the loss of land after three cyclonic events (Fani, Bulbul and Amphan) that occurred in 2019 and 2020 along the entire Sundarbans coastline. It categorizes these losses based on the history (since 1985) of shoreline dynamics (permanent, seasonal, and ephemeral) after the three cyclones. Remote sensing datasets and machine learning algorithms are utilized for classifying shoreline dynamics and detecting change through the Google Earth Engine platform. The shoreline areas where seasonal changes took place between 1985 and 2018 lost the highest proportion of land after a cyclonic event. Additionally, on comparing losses between previously eroding and accreting areas, cyclonic events cause a higher loss in the previously accreting areas. Thus, this study not only shows that the legacy of past disturbances shapes mangrove forest structure in cyclone-prone areas but also highlights the spatial differences in the vulnerability of areas. It is recommended that along with preventing erosion of mangroves, it is equally essential that accreting and seasonally changing shorelines are protected.