Introduction
Land subsidence, as one of the most severe manifestations of land degradation, is commonly the consequence of excessive groundwater withdrawal and quantitative and qualitative alterations in aquifer systems. This irreversible phenomenon represents one of the final stages of desertification and can severely disrupt the ecological and economic functions of the land. In most desertification assessment models and indices, emphasis has traditionally been placed on climatic, edaphic, and vegetation factors, while land subsidence has been less frequently considered as an independent and influential indicator. In recent years, however, new approaches to desertification assessment have sought to integrate groundwater-related indicators—such as groundwater level decline, electrical conductivity (EC), and sodium adsorption ratio (SAR)—with subsidence rate and extent, in order to provide a more comprehensive understanding of land degradation. Within this framework, models such as IMDPA and its extended versions, by incorporating subsidence as a key criterion, enable the reclassification of desertification severity and the more precise identification of critical zones. Such approaches not only enhance the accuracy of assessment models but also contribute significantly to preventive policymaking, sustainable water resource management, and mitigation of desertification processes. Accordingly, integrating hydrogeological data with geomechanical indicators, such as land subsidence, is a crucial step in analyzing and monitoring land degradation processes. The present study aims to evaluate the role of groundwater level decline, water quality deterioration, and land subsidence in desertification and land degradation in the Abarkouh–Sirjan watershed using the IMDPA model.
Materials and Methods
To this end, thematic layers of groundwater-related indicators—including groundwater level decline, electrical conductivity, sodium adsorption ratio—and land subsidence maps were prepared and classified in terms of desertification risk. Subsequently, by integrating the qualitative and quantitative groundwater degradation maps with the land subsidence map (considered as a soil criterion) through a regional averaging approach, the final desertification severity map was generated. Ultimately, the spatial distribution of desertification intensity was mapped using final desertification risk classes derived from the averaged values of the individual indicators.
Results and Discussion
For the evaluation of desertification status, groundwater quality indicators (EC and SAR) were first examined. Since land subsidence data for the Abarkouh–Sirjan basin were available for the 2015–2016 hydrological year, groundwater quality indices were assessed for 2015–2016 and 2016–2017, and their spatial averages were calculated. Results indicated that approximately 60% of the groundwater resources in the study area exhibited high salinity levels (EC exceeding 5,000 μS/cm). The spatial distribution of SAR revealed that, except for Sirjan and Ghotrooyeh playas (values between 18 and 26), SAR values across the rest of the study area were generally below 18 (low category). The regional average groundwater level decline was about 54 cm for the entire area and 57 cm for aquifers, with variations ranging from 1 cm to 237 cm across the basin. Moreover, land subsidence was most pronounced in the Abarkouh, Bavanat, and Sarchahan aquifers, classified within moderate to very severe categories. The final map demonstrated that more than 90% of the study area fell within moderate to very severe desertification intensity classes.
Conclusion
Introduction
Land subsidence is recognized as one of the most severe manifestations of land degradation, commonly resulting from excessive groundwater extraction and significant changes in both the quantity and quality of aquifer systems. This irreversible phenomenon can disrupt ecological functions, including soil stability, vegetation productivity, and water retention, as well as economic activities such as agriculture and water-dependent industries. In arid and semi-arid regions, land subsidence often represents a terminal stage of desertification, signaling a critical imbalance between resource extraction and natural system resilience. Despite its importance, most traditional desertification assessment models and indices have historically focused on climatic factors, soil properties, and vegetation cover, while largely overlooking land subsidence as an independent and influential criterion.

Recent advances in desertification research emphasize the need for integrative assessment approaches that combine hydrogeological and geomechanical indicators. Groundwater-related factors—such as groundwater level decline, electrical conductivity (EC), and sodium adsorption ratio (SAR)—provide essential information about aquifer stress and water quality deterioration, while subsidence measurements capture the physical response of soil and sediments to prolonged extraction. Integrating these datasets enables a comprehensive evaluation of land degradation processes and the identification of critical zones that may be underestimated when using conventional indicators alone. In this context, the Integrated Monitoring and Desertification Prediction Assessment (IMDPA) model, including its extended versions, has proven effective. By incorporating land subsidence as a key criterion, IMDPA allows refined classification of desertification severity, more precise identification of vulnerable areas, and improved guidance for sustainable resource management.

Materials and Methods
The present study focuses on the Abarkouh–Sirjan watershed, a semi-arid to arid region in central Iran characterized by high interannual variability in precipitation and intensive groundwater use. To evaluate the contribution of groundwater level decline, water quality deterioration, and land subsidence to desertification, thematic layers of hydrogeological and geomechanical indicators were developed. These layers included maps of groundwater level decline, EC, SAR, and land subsidence. Each indicator was classified according to desertification risk levels. Subsequently, qualitative and quantitative groundwater degradation maps were integrated with the land subsidence map, considered as a soil criterion, using a regional averaging approach. This integration produced a final desertification severity map reflecting the combined effects of hydrological and geomechanical factors on land degradation.

Results and Discussion
Analysis of groundwater quality indicators revealed widespread deterioration across the watershed. Approximately 60% of groundwater resources exhibited high salinity levels (EC > 5,000 μS/cm), indicating substantial ionic accumulation due to prolonged extraction and limited natural recharge. SAR values were generally below 18 (low sodicity), except in localized playa areas such as Sirjan and Ghotrooyeh, where values ranged between 18 and 26. Groundwater level decline displayed significant spatial variability, with a regional average of 54 cm and localized extremes reaching 237 cm, highlighting the heterogeneous response of aquifers to extraction pressures and the need for site-specific management interventions.

Land subsidence was most pronounced in the Abarkouh, Bavanat, and Sarchahan aquifers, classified within moderate to very severe categories. Incorporating subsidence into the IMDPA model substantially influenced the final desertification classification, revealing critical zones that could have been underestimated if only hydrological or climatic factors were considered. The final desertification map indicated that over 90% of the watershed falls within moderate to very severe intensity classes, with approximately 40% categorized as severe and 10% as very severe. Areas experiencing substantial groundwater decline and high subsidence rates correspond closely with regions of highest desertification severity, confirming the interdependent role of hydrological stress and soil compaction in land degradation.

These findings have significant implications for land and water resource management. Identification of zones affected by both groundwater depletion and pronounced subsidence provides a basis for targeted interventions, including controlled groundwater abstraction, artificial recharge, and soil stabilization measures. Integrating hydrogeological and geomechanical data enhances the predictive capacity of desertification assessment models, supporting informed policy-making and prioritization of mitigation efforts. Continuous monitoring and multi-criteria evaluation are essential to capture the dynamic interactions between aquifer depletion, water quality degradation, and land subsidence that drive desertification processes.

Conclusion
Land subsidence is confirmed as a pivotal criterion in desertification assessment, capable of revealing critical areas of vulnerability that may not be apparent when relying solely on conventional indicators. Integrating quantitative and qualitative groundwater indices with geomechanical data facilitates a comprehensive evaluation of land degradation, supporting both scientific understanding and practical management. The Abarkouh–Sirjan watershed serves as a representative case illustrating the complex interactions between anthropogenic pressures and natural system responses in arid and semi-arid environments. The study emphasizes the necessity of adopting integrative assessment approaches and highlights the crucial role of subsidence monitoring in sustainable land and water resource management. Future research should refine multi-indicator models, incorporate additional environmental stressors, and assess the long-term effectiveness of interventions aimed at mitigating land degradation and enhancing ecosystem resilience