Coastal Subsidence Contributing to Relative Sea-Level Rise: a Case Study on Gujarat’s Cities Along the Gulf of Khambhat, India

The research investigates combining InSAR-derived vertical land motion (VLM), tide gauge observation, sea-level-rise (SLR) projections, and historical storm surge data to evaluate 21st-century inundation risk maps over the coastal cities along the Gulf of Khambhat in Gujarat, India. The area of interest includes three major coastal districts, i.e., Surat, Bhavnagar, and Bharuch, along the Gulf region. We explored ESA’s Sentinel-1 C-band sensor data from March 2020 to June 2023 to obtain VLM over the region using the SBAS-based multi-temporal radar interferometry (MT-InSAR) technique. The findings indicate a deformation rate of $\gt5 \mathrm{~mm} /$ year observed in different parts of the Surat, Bhavnagar, and Bharuch districts, which is comparable well with the dense building footprints as an indicator of anthropogenic activity. Combining relative SLR and VLM data, we predict inundation risk model data over the Gulf area for the years 2030, 2050, and 2100 under different SSP scenarios. Under the SSP5-8.5 scenario, inundated areas will be approximately $16.05 \mathrm{~km}^{2}, 22.73 \mathrm{~km}^{2}$, and $59.50 \mathrm{~km}^{2}$ by the years 2030, 2050, and 2100, respectively. The anticipated storm surge information could further amplify the risk of inundation over the study region.