Land subsidence is a complex geomorphological phenomenon characterized by the vertical downward movement of the Earth's surface, with far-reaching implications for ecosystems, human infrastructure, and the environment. This study aims to analyze the relationship between groundwater level decline and land subsidence in the Tehran-Shahryar plain, using measured data. The research methodology is based on advanced remote sensing techniques, including Interferometric Synthetic Aperture Radar (InSAR) using Sentinel-1 satellite images, and analysis of groundwater level data using statistical methods. A key innovation of this research is the simultaneous use of all available piezometers in the study area and the calibration of radar data with accurate ground leveling measurements. The findings of the study indicate that groundwater level decline is the main trigger of subsidence in the region. Cross-correlation analysis of the data reveals a time lag of 0 to 3 years, with an average of 1 year, between groundwater level decline and the occurrence of subsidence across the entire area. This time lag is due to complex geotechnical processes in the water-bearing sedimentary layers, especially in areas with complex geological structures. Spatial-temporal analyses show that the Tehran-Shahryar plain is facing a high potential for subsidence, with average subsidence rates exceeding 23 mm per year in some areas. This trend can pose serious threats to critical infrastructure, engineering structures, and the region's ecosystem. The implications of this study highlight the importance of integrated groundwater management, controlled extraction, and continuous monitoring of geodynamic changes. Moreover, the results can provide a suitable scientific basis for making major decisions in water resources management and mitigating environmental hazards.