Coastal line-of-sight deformation and relative sea level rise in Kochi, South India: Insights from PS-InSAR, tide gauge, and satellite altimetry analyses

Kochi serves as a strategic economic nexus on the southwest coast of India along the Arabian Sea. The study employed PSInSAR using 251 Sentinel-1 A/B C-band descending-track SAR scenes (2016–2024) to monitor coastal LOS velocity, revealing suburban rates reaching up to −15 mm/year, with cumulative LOS displacements up to 120 mm. Spatially varying LOS displacement was synergistically analysed with LULC changes (1992, 2016, 2024) and lithological units to elucidate potential drivers. Urban area increased by 400.04% from 1992 to 2024, reaching approximately five times its 1992 extent, at the expense of vegetation, which declined by 163.40 sq. km, reflecting a 3.8-fold increase in loss rate. Geospatial overlay analysis shows unconsolidated lithologies, such as palaeo-marine deposits and Pleistocene sands, undergo significant LOS displacement. Long-term tide gauge records (1940–2022) were analysed to quantify SLR using linear and piecewise regression. Linear regression indicates a mean rise of 1.91 ± 0.20 mm/year, while piecewise regression identifies three phases: rapid rise during 1940–1960 (6.57 mm/year), declining phase during 1960–1988 (−1.58 mm/year), and renewed acceleration during 1988–2022 (4.14 mm/year). Satellite altimetry-derived sea-level anomalies corroborated these trends, yielding strong positive correlation with tide-gauge observations (Pearson's r = 0.8). The synergy between LOS displacement and SLR intensifies vulnerability.