Integrated AHP and DInSAR Approach for Land Subsidence Hazard Assessment in Karaj Plain, Iran

Land subsidence (LS) is a significant environmental issue affecting more than 50% of Iranian plains, particularly Karaj Plain located on the southern slopes of the Central Alborz, Iran. This study applied the Analytical Hierarchy Process (AHP) to create a LS hazard susceptibility map, considering factors such as groundwater drawdown, soil texture, alluvium thickness, distance between fault lines, and permeability. The resulting map was then compared with the Differential Interferometric Synthetic Aperture Radar method. The sensitivity mapping analysis revealed that 33.2% of the northwest-southeast direction in the studied area is classified as high- to very-high-risk. Moreover, analysis of Sentinel-1A images spanning eight years and three months (from October, 2014, to January, 2023) indicated that the maximum LS rate (158 mm/year) occurred in the central and northwestern parts of the study area, particularly within 200 to 300-meter thick layers containing significant clay layers. Over the past three decades, the Karaj plain has experienced groundwater depletion at an average annual decline of 0.9 meters. The five LS control points exhibited a strong negative correlation ranging from 66% to 88% with groundwater decline. Notably, this correlation suggests that maximum soil consolidation occurs with a two-year lag. Plus groundwater decline, a comparative study of two methods demonstrated that soil texture and alluvium thickness play a significantly influential role in asymmetric LS, especially considering the young age of the sediments and the presence of clay lenses. The accuracy of the generated LS hazard maps was validated using the ROC curve, achieving a high AUC of 0.773.