Assessment of land deformation and groundwater depletion using Sentinel-1 PS InSAR, GRACE, and Borehole data

This study integrates remote sensing, groundwater monitoring, and geospatial techniques to investigate groundwater dynamics and land deformation in Lahore, Pakistan. PS InSAR technique was utilized from 2014 to 2023 to identify significant land subsidence trends, with 246,843 permanent scatter points produced. Land Deformation, ranging from 0.7 to −4.3 cm/year, was observed, particularly from −2.5 to −4.3 cm/year in densely built-up areas. The analysis revealed at the county-scale (administrative unit) varying levels of subsidence, with Model Town county experiencing the most pronounced deformation with significant subsidence in the Township and its neighboring Union Councils (UCs). Groundwater Storage Anomaly (GWSA) assessments using GRACE Satellite data showed a rapid decline in groundwater storage, particularly in Cell B (−0.77 tau) of the JPL Mascon dataset and across all cells in the CSR Mascon dataset. Depth to Water (DTW) measurements from groundwater monitoring wells indicated significant spatial variations in groundwater levels, with central Lahore exhibiting considerably higher median DTW values than suburban areas. Additionally, correlation analysis using Spearman's method revealed strong associations, particularly in Model Town county, among all GRACE cells (>0.75 ρ), and with DTW in high-subsidence areas. Trend and slope analysis have also been conducted to support these findings further. The study recommends validating InSAR data with Global Navigation Satellite System (GNSS) measurements and GWSA with water table data of small intervals to enhance the accuracy and reliability of land deformation and groundwater assessments. These findings aid policymakers and urban planners in sustainable groundwater management and land use planning in Lahore.