SBAS-InSAR Analysis of Coastal Subsidence in Kerala, India, to monitor Flood Inundation Risk due to Relative Sea Level Rise

The coastal sinking of land in many low-lying regions in the world has a greater potential risk of flooding-inundation hazards due to relative sea level rise. Kerala, being known for its varied geographical features, sharing a long coastline of 590 km in the southern part of India, has been affected by several floods in the past few decades. To develop an effective coastal subsidence monitoring system and predict the hazard risk, this study makes use of the Multi-Temporal Synthetic Aperture Radar (MT-InSAR) technique using Sentinel-1 data to obtain the Vertical Land Motion (VLM) over the Kerala coast and projects till 2100. The VLM results derived from the InSAR technique reveal a large subsidence of more than 20mm/year in the Kuttanad region of Alappuzha district. Further, we incorporate the VLM, the future projection of sea level from the Intergovernmental Panel on Climate Change (IPCC) AR6 report, and the high spatial resolution of the Digital Elevation Model (DEM) to map the low-lying fast subsiding zones that are prone to future flood inundation due to relative sea level rise. We derive future flood inundation maps for the years 2030, 2050, 2070, and 2100 by considering various socio-economic scenarios.