Unveiling the Impact of Groundwater Extraction on Local Land Subsidence and Calibrating a Model for Understanding the Mechanics of Mixed Subsidence and Uplift Phenomena in Gujarat, India

 

Local land subsidence (LLS) is caused by groundwater overextraction, long-term oil and gas extraction without pressure maintenance, and the natural compaction of sediments due to self-weight. Among these factors, the groundwater-induced LLS has intensified markedly in urbanized landscapes and groundwater-irrigated agricultural regions worldwide. Although LLS contributes to vertical land motion, its spatial extent, temporal persistence, and magnitude are generally smaller than those associated with regional tectonics or glacial isostatic adjustment. Consequently, global concern regarding groundwater-driven LLS has remained limited, particularly for non-coastal cities where subsidence does not directly exacerbate local relative sea-level rise. However, LLS increasingly threatens the long-term integrity of aquifer systems, urban infrastructure, and the sustainability of cities dependent on alluvial groundwater resources. In Indian metropolitan regions, LLS has been discussed over the past two decades, yet interpretations have largely been confined to InSAR-derived displacement velocities and their correlations with groundwater-level fluctuations. Here, we reevaluate these prevailing assumptions in Ahmedabad, the economically vibrant city of the western Indian state of Gujarat, by integrating stratigraphic, hydrogeologic, geodetic, geochemical, and demographic datasets. We combine eight years of InSAR observations with three years of continuous GPS measurements to characterize the spatial and temporal evolution of subsidence across the city. Our results show persistent subsidence footprints in the southwest sector of Ahmedabad, coinciding with a major industrial hub, and in the western outskirts, which have undergone rapid residential development since 2017. Subsidence initiated in the southwest, corresponding to the historic urban core, whereas the maximum subsidence rate, reaching 2.7 cm/year, occurs in the western peripheral zone of Bopal. Time-series analysis of InSAR-derived displacements reveals a superposition of inelastic, elastic, and uplift components, indicating that subsidence is nearly irreversible in some sectors while substantial recovery is observed elsewhere. Contrary to conventional interpretations, no direct relationship is identified between land displacement and groundwater-level fluctuations in Ahmedabad. Instead, a strong positive relationship emerges between subsidence-uplift patterns and the proportions of clay and sand in local lithofacies. In May 2004, which perhaps marks the pre-consolidation head, the groundwater levels show dominant recovery trends within the confined-1 and confined-2 aquifer systems, accompanied by seasonal variability. Recovery in shallow aquifers could be due to severe groundwater pollution associated with textile industries in the Vatva and Lambha localities, rendering these waters unsuitable for consumption. The present study develops a numerical model that calibrates delayed clay compaction relative to pre-consolidation head, skeletal storage coefficients, and the number of compacting aquitards. This framework is transferable to alluvial aquifer systems globally, enabling improved assessment of residual compaction and recharge dynamics beyond traditional interpretations in the Indian subcontinent.