Introduction

Land subsidence as an anthropogenic geomorphological hazard has caused irreversible damage to infrastructure, water resources, and environmental stability in recent decades, especially in alluvial plains of arid and semi-arid regions of Iran. Alborz province, due to its transitional position between the Alborz mountain range and the central plains, the presence of fine-grained Quaternary sediments, excessive groundwater extraction, rapid urban and industrial development, and significant reduction of agricultural lands and water bodies, is considered one of the critical subsidence hotspots in the country. Despite scattered previous studies, few researches have simultaneously and integrally analyzed land use/land cover changes and subsidence rates with an anthropogenic geomorphology approach and feedback loop modeling. The main objective of this research is to analyze the spatio-temporal relationship between land subsidence and land use/land cover changes in the southern plains of Alborz province (Eshtehard, Hashtgerd, and Qazvin) during the periods 2016-2020 and 2020-2025, with emphasis on explaining causal cycles and developing a conceptual model of anthropogenic geomorphology.



Methodology

The present study is applied in terms of purpose and descriptive-analytical in nature, based on remote sensing and geographic information system data. To extract subsidence rates, 10 Sentinel-1 radar images (C-band, interferometric mode, ascending pass) were used during two time periods: 2016-2020 and 2020-2025. Radar data processing in SNAP software included orbit application, interferogram formation, Goldstein filtering, phase unwrapping, and topographic correction using the Range-Doppler method. The final phase was converted to vertical displacement, and the annual subsidence rate was classified into three categories: low (less than 10 cm/year), medium (10-20 cm/year), and high (more than 20 cm/year). To prepare land use/land cover maps for 2016, 2020, and 2025, Sentinel-2 (10 m resolution) and Landsat-8 (30 m resolution) optical images were classified using the maximum likelihood supervised classification algorithm in ENVI software. Four land use classes including barren lands, riverine areas, agricultural lands, and residential areas were defined, and validation was performed using 250 field control points and Google Earth images (overall accuracy above 85%). In the ArcGIS environment, subsidence and land use maps were integrated using spatial overlay and zonal statistics methods. The mean subsidence rate for each land use class was calculated, and land use transition matrix and hot spot analysis (Getis-Ord Gi* statistic) were performed to identify spatial autocorrelation patterns.

Results and Discussion

Land use change results showed that during 2016-2025, agricultural lands decreased by 50% (from 33,610 ha to 16,751 ha) and riverine areas decreased by 51% (from 4,032 ha to 1,950 ha). In contrast, barren lands increased by 43% (from 199,389 ha to 210,224 ha) and residential areas increased by 32% (from 15,356 ha to 20,319 ha). These changes indicate a transition from natural-productive functions to anthropogenic and non-productive functions, accompanied by reduced aquifer recharge, increased groundwater extraction, and intensified surface desiccation. The highest annual subsidence rate during 2020-2025 ranged between 23-25 cm/year, and the maximum cumulative subsidence was approximately 1.1 m in southern Fardis and northern Eshtehard, showing an 18 cm increase compared to the previous period (92 cm). Critical subsidence zones (more than 0.5 m) expanded from 35% in the first period to 45% in the second period, and the subsidence center migrated northeastward (along the Eshtehard-Fardis-Hashtgerd industrial axis). Spatial overlay analysis showed that the highest subsidence intensity occurred in barren lands (69,716 ha in the first period and 59,135 ha in the second period in the high-intensity class), which is attributed to aquifer desiccation, reduced pore pressure, and high compressibility of fine-grained sediments. Next, residential areas with 9,201 ha (first period) and 15,103 ha (second period) in medium to high subsidence zones indicate the role of increased surface load from urban structures in exacerbating layer compaction. Agricultural lands also contributed significantly to subsidence with 15,693 ha in the medium class (first period) and 15,253 ha (second period), resulting from excessive groundwater extraction for irrigation and water table decline. Spatial autocorrelation analysis (Gi* statistic) revealed that areas with positive correlation (hot spots) mainly coincide with barren land expansion and urban development in southern Fardis and northern Eshtehard (99% confidence level). The conceptual model (Figure 7 in the article) explains five main nodes including urban/industrial development, barren land expansion, groundwater extraction and water table decline, fine-grained layer compaction and subsidence, and ecological instability through two positive feedback loops: the first feedback loop (urban development ↔ increased groundwater extraction ↔ aquifer decline ↔ intensified subsidence) and the second feedback loop (subsidence ↔ runoff concentration ↔ vegetation degradation ↔ barren land expansion ↔ renewed subsidence intensification).

Conclusion

This research, by integrating Sentinel-1 radar data with Sentinel-2 and Landsat-8 optical data within a GIS and spatial statistics framework, and by presenting the first conceptual model of anthropogenic geomorphology for the southern plains of Alborz, demonstrated that land subsidence is a multi-causal phenomenon resulting from the interaction of land use changes, groundwater level decline, and compressibility of fine-grained sediments. The more than 50% reduction in agricultural lands and water bodies, simultaneously with a 43% increase in barren lands and 32% increase in residential areas, indicates a shift in the earth system equilibrium from a natural to an anthropogenic and unstable state. The highest subsidence rates (23-25 cm/year) and cumulative subsidence (1.1 m) are concentrated in southern Fardis and northern Eshtehard, and critical zones have expanded from 35% to 45%. The most important innovation of this research is the explanation of the positive feedback cycle among urban development, barren land expansion, groundwater extraction, and subsidence intensification, demonstrating that subsidence is not merely a physical phenomenon but an indicator of human-earth system instability in the region. Based on the findings, controlling subsidence in the southern plains of Alborz requires (1) integrated water resources management and a ban on excessive groundwater extraction, (2) revision of urban development patterns and prevention of horizontal urban expansion over subsidence-prone areas, (3) restoration of vegetation cover and agricultural lands to enhance aquifer recharge, and (4) continuous monitoring using InSAR techniques and machine learning-based prediction models.