Adjustment of the Coastal Communities in Response to Climate Variability and Sea Level Rise in the Sundarban, West Bengal, India

Abstract

The deltaic coast of Sundarban is liable to flooding, erosion, overwash dynamics, sediment surface reactivation, shoreline retreat, and habitat destruction at the sea face and along the mouths of tidal rivers and estuaries. Sandy beaches fringed with sand dunes disappeared from many places of the coastline extending from the Hugli River mouth islands to Thakuran River mouth point in Indian Sundarban. Mangroves are removed from the shoreface and are severely damaged in the backshore tidal flats due to increased hypersalinity , inland encroachment of overwash sand fan lobes and active shoreline retreat by repeated cyclone landfalls.The high-magnitude storms, their intensity and frequency, and the changing direction of approach to the low-lying shoreline (1.7 m to 4.26 m above the m s l), the strong evaporation rate in the dry period, and the shortages of freshwater supply into the coastal zones due to infrequent river floods can be highly damaging to the beaches, sand dunes, and mangroves. The assessment of global mean sea level rise by IPCC (fifth assessment report) with long-term projection (up to 2100) and short-term projection (1986–2005) indicated about the occurrences of 0.98 m rise and 2.4 m rise, respectively, in the coastal region. However, the relative rise of sea level will be more significant in the deltaic coast due to sedimentation in the inner estuaries and subsidence of the reclaimed land. The high energy wave breakers and their direction of travel corresponding with the cyclone landfalls, strong southwest monsoon winds, and periodicity of astronomic tides (HAT phase) have exposed the inability of sandy shores to withstand against the forcing factors at present.In absence of the shoreline buffers (wide sandy beaches, sand dunes, and mangroves), the coastal communities are directly exposed to the forcing factors of advancing sea in the Sundarban. Weaker embankments are repeatedly damaged in every cyclone, and many settlements are abandoned due to such climate variability and related effects of coastal squeeze between the rising sea and the sea walls or earthen embankments in the reclaimed Sundarban. People of the seafront areas have migrated inland for temporary rehabilitation in favorable areas, or many among them converted into environmental refugee due to the loss of their livelihood and settlement sites.The potential erosion of sandy beaches, sand dunes, and mud banks are analyzed using satellite-derived database (ALOS PALSAR DEM, Landsat 8 OLI/TIRS, and Google Earth) and repeat survey across the shore transects in the region at regular interval. IMD cyclone data and INCOIS-generated wave data are also used in the present study to highlight their nature of change along the shoreline. The responses of coastal communities against the climate variability are studied in the field by survey methods. Coastal management needs to adopt more environmental measures than the implementation of expensive protective measures in the vulnerable sites of the deltaic coasts to withstand the forcing factors at present.KeywordsOverwash dynamicsClimate variabilityCoastal squeezeSea level riseMarine forcing factorsAbandoned settlements and environmental refugee