Monitoring ground deformation in recent years in Western Ganga delta India, using persistent scatterer interferometry on multi-temporal ALOS-2 L band imaging radar data

ALOS-2 L band SAR is used to calculate the vertical deformation rates and the time series of cumulative deformation in the Western Ganga delta (South 24 parganas district, West Bengal, India that including the world heritage site of Sunderbans) from 2015 to 2022. There are several reports of vanishing islands and coastal inundations in this area. But very little is known about the land subsidence which might complement the climate-change-related absolute sea level rise. Persistent Scatterer Interferometry, a special class of Differential Interferometry is used to detect ground movement in the millimeter scale. The range of subsidence observed in the study area is from 9.9 to 0.5 mm/ year. Average displacement rate varies from − 2.4 to − 2.8 mm/year while maximum areas record a subsidence ranging between − 1.8 to − 2.9 mm/yr. Very high to high subsidence is observed east of Matla river in Buffer zone 2 and 3. The highest subsidence is seen in the southern parts of West Ajmalmari Island and western section of Burge Island. Very high subsidence (− 9.5 to − 9.2 mm/yr) is also recorded in and around Jatar Deul in the northern inlands. Small pockets of upliftment (2.5 to 4.5 mm/year) are also observed. Upliftment zones are more prominent in the semi-urban set up in the north than in the Sunderbans region. High subsidence values in these mangrove-covered islands of buffer zone 2 and 3 is in concordance with south-easterly basin subsidence and neo-tectonism as indicated by Holocene isopach maps. Our study suggests that the central part of the Indian Sunderbans is undergoing more tectonic activity than the eastern core forest region. The results have been compared with seasonal peizometric level and a direct relation of subsidence/upliftment with ground water extraction has been established.