Quantifying spatiotemporal land subsidence rates and deformation hotspots using integrated GNSS and InSAR in Nakuru County, Kenya

Land subsidence is an emerging environmental and geohazard challenge in groundwater-dependent and tectonically active regions. This study quantified the spatiotemporal distribution of land subsidence in Nakuru County, Kenya, between 2014 and 2024 using an integrated Persistent Scatterer–Small Baseline Subset (PS–SBAS) Interferometric Synthetic Aperture Radar (InSAR) approach supported by Global Navigation Satellite System (GNSS) validation and spatial statistical analysis. A total of 124 Sentinel-1 A ascending-orbit scenes were processed using SNAP 10.0, incorporating SNAPHU phase unwrapping, ERA5 atmospheric correction, and line-of-sight to vertical displacement conversion. The results revealed widespread but spatially heterogeneous subsidence, with deformation rates ranging from approximately 20.507 mm/yr to − 28.519 mm/yr. The highest subsidence rates occurred within the central and southeastern parts of Nakuru County, where hotspot analyses identified statistically significant deformation clusters. Temporal analysis indicated a gradual increase in both deformation magnitude and spatial extent over the monitoring period. Validation using four GNSS stations produced a mean bias of -0.61 mm/yr and a root mean square error (RMSE) of 0.99 mm/yr, confirming the reliability of the InSAR-derived estimates. Groundwater storage analysis revealed a strong spatial association between groundwater-rich environments and subsidence-prone areas, suggesting that hydrogeological conditions influence deformation susceptibility. The study demonstrates the effectiveness of integrating InSAR, GNSS validation, hotspot analysis, and groundwater assessment for regional subsidence monitoring and provides valuable information for groundwater management, infrastructure planning, and environmental sustainability within the Kenya Rift.