Vulnerability and Impact Assessment of Land Subsidence using Persistent Scatterers Interferometry (PSI) for Chennai, India.

Abstract In the recent years, India has witnessed a rapid economic growth resulting in unplanned urbanization and a continuous migration of rural population to cities. A coastal megacity like Chennai is vulnerable to hazards such as land subsidence caused by the over exploitation of groundwater and an increasing load on its surface. An important consequence of this can be the heightened vulnerability of a large population to climate change in the form of increased flood inundation and sea level rise. Our study reports the first scientific assessment of land subsidence for the Greater Chennai Corporation (GCC) area which was conducted using the Persistent Scatterers Interferometry (PSI) method. The results of the average displacement velocity ranged between -30.66 to 25 mm/yr. Due to an uplift pattern occurring in some regions, the average subsidence rate calculated was -1.20 mm/yr, with a standard deviation value of 3.58. The results of the time series analysis showed the central business district of the city, zone 10 (Kodambakkam) to be subsiding steadily and consistently, with the rate of subsidence reaching -65 mm/yr in 2019. A strong positive correlation was found between the land subsidence rates and the groundwater levels for GCC based on a Pearson’s correlation coefficient (r) of 0.81 and a coefficient of determination (r2) of 0.66. The study further showed a high degree of spatial overlap between the historical flood inundation data and land subsidence prone areas and also scrutinized the potential impact of the hazard on the railway infrastructure of the city.