Response of the Sundarbans coastline to sea level rise and decreased sediment flow: A remote sensing assessment

The Sundarbans is the world's largest remaining single block of mangrove forest, covering approximately 1 million ha (~ 10,000 km 2) of the Ganges–Brahmaputra delta along the coastal areas of India and Bangladesh. Sea level rise and alteration of water flows of the Himalayan headwaters are among the major disturbances threatening these coastal areas. But very few studies exist on the dynamics or current status of the Sundarbans coastline. We used Landsat images spanning from 1973 to 2010, and an algorithm that we developed, to consistently estimate the spatiotemporal dynamics of erosion and accretion for four different time intervals and the whole study period. Our results show that the direction and extent of erosion and accretion rates varied throughout the different periods. Erosion was the highest in the 1973–1979 interval, with 23.2 km 2 year −1 of land loss. However, that rate substantially declined in the following periods, reaching a rate of 7–10 km 2 year −1. Accretion showed a rate of 10 km 2 year −1 between 1973 and 1989, but substantially declined to ~ 4 km 2 year −1 between 1989 and 2010. Accretion rate has declined in the recent years but erosion rate has remained relatively high. As a result the delta front has undergone a net erosion of ~ 170 km 2 of coastal land in the 37 years of our study period. These numbers are significantly higher than the previously reported rates and magnitudes of erosion in this area. The methods and maps developed in this study may be helpful in management planning of this vulnerable coastline. ► Sea level rise and sediment reduction impact delta fronts. ► Satellite imagery can be used to estimate erosion and accretion along coastlines. ► The Sundarbans coastline of the Bengal delta is a dynamic system. ► Rates of erosion and accretion vary spatially and temporally. ► Accretion rate is decreasing and the coastline is currently in a state of net erosion.