Spatiotemporal Trends of the Bay of Bengal Shoreline Retreat along the Sundarban Coasts and the Relevant Carbon Implications

The coastal areas of the Bay of Bengal along the Ganges-Brahmaputra (GB) delta are low-lying and highly vulnerable to natural disasters, such as flooding and cyclones. The modern GB delta was formed within the large Bengal basin during the last 11,000 years, and it extends offshore in the Bay of Bengal. The coastal areas of this delta harbor the world’s largest continuous patch of mangrove forests, the Sundarbans, covering approximately one million hectares, ~60% of which is in Bangladesh and the rest is in India. Studies have shown that the GB delta is still undergoing accretion at a rate of up to 1.1 cm per year. But remote sensing studies have also indicated that the shoreline and shallow offshore areas of the western delta front are currently in a net erosional state at a rate of about 1.9 square km per year, with a coastline retreat of as much as 3-4 km since 1792. Other studies have quantified the land loss at 38 square km in since 1973. But no study to date has reported the details of spatiotemporal patterns of land loss along the Sundarbans coastline, or their drivers. Under global climate change and the related sea level rise, proper understanding of how the coastlines are changing and the drivers of those changes would be essential to mitigate the impacts on the coastal mangrove forests. In this study we used a time series of Landsat MSS and TM images from 1973 to 2010 to systematically explore the spatiotemporal distributions and trends of land loss along the Sundarbans coastline of Bangladesh and India. We also used data from a host of published studies on Bay of Bengal surface currents, cyclone tracks, sea level rise, monsoonal rainfalls, sediment flow, land subsidence and anthropogenic factors to deduct probable cause-effect relationships of the trends in coastal land loss. Finally we estimated the carbon loss of the mangrove forests due to the shoreline retreat, and using IPCC scenarios we predicted the future carbon implications of these mangrove ecosystems under global climate change.