نوع مقاله : مقاله پژوهشی
نویسندگان
1 نویسنده مسئول، استادیار پژوهش، بخش تحقیقات بیابان، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
2 استاد پژوهش، بخش تحقیقات گیاهشناسی، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
3 استادیار پژوهش، بخش تحقیقات بیابان، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
4 محقق، بخش تحقیقات بیابان، مؤسسه تحقیقات جنگلها و مراتع کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and Objective: In recent decades, environmental consequences of excessive groundwater extraction—driven by population growth and agricultural development—have caused irreparable losses to ecosystem structure, including land subsidence. Land subsidence can be regarded as the final stage of land degradation in arid and desert regions. Semnan Province is the third arid/desert province in Iran and has become a migration destination in recent years due to its location along the Tehran–Mashhad corridor. This study aims to assess land degradation using the original IMDPA (Iranian model of desertification potential assessment) and the developed IMDPAS (Iranian model of desertification potential assessment with subsidence), based on two main criteria: groundwater status and the rate of land subsidence in Semnan Province.
Methodology: According to the study objectives, this work models and numerically evaluates land degradation in six areas subject to land subsidence—Ivanaki, Garmsar, Semnan, Damghan, Bastam, Shahroud, and Miami—in Semnan Province. The assessment employs the principal IMDPA model and its extension (IMDPAS), integrating two groundwater criteria—level-drop indices, electrical conductivity (EC), and sodium adsorption ratio (SAR)—along with a land-subsidence-rate criterion. Groundwater level-drop data were obtained from piezometric and observational wells for 2015–2016, while water-quality data for 2014–2018 were sourced from the Ministry of Energy. To characterize subsidence, radar interferometry analyses were conducted using two Sentinel-1 A (SLC) acquisitions from August to December 2016, provided by the Geological and Mineral Exploration Organization. Subsequently, study areas were zoned by subsidence rates after scoring and classifying degradation severity for each criterion. The numerical degradation assessment was then repeated by (i) computing the geometric mean of the two main criteria and applying the original IMDPA classification, and (ii) reclassifying using a new proposed scheme. Finally, results were analyzed through comparative assessments.
Results: The results indicate notable spatial differences in degradation when assessed with groundwater criteria (water level drop, EC, and SAR) and subsidence data. Based on water depletion, EC and SAR showed land degradation of 87%, 57%, and 100% as degraded in the whole province, while the largest shares were in Damghan, Garmsar, and Shahrood areas. Subsidence analysis for Semnan Province shows that the subsidence rate in 2016 varied, with 62% of subsiding areas falling into the medium class (1.5–3 cm); Shahrood accounts for 38% of this medium-class subsidence. The sole observed site in the very severe subsidence category (>6 cm) is in Garmsar.
Applying the original IMDPA classification, 99% of the province fell within the moderate degradation class. When reclassified using the developed IMDPAS scheme, the severity class shifts to a 40% increase in the severe category, indicating that the areas with the highest land degradation intensity shift to Shahrood, Semnan, Ivanaki, and Miami under the new scheme. A finer-scale analysis of agricultural land use from 2011–2021 shows an expansion of irrigated garden crops in Garmsar, Damghan, and Shahrood, corroborating the observed degradation patterns and groundwater withdrawals in these areas.
Conclusion: Examining land degradation in Semnan Province—one of Iran’s three arid/desert provinces with a dry climate, recurrent droughts, limited rainfall and water resources, and a naturally declining water table—reveals a critical ecosystem state when assessed using groundwater criteria and land-subsidence rates. The findings underscore the need to revisit the class definitions in land-degradation indicators and criteria to reflect the fragile conditions of arid/desert ecosystems. Moreover, analyses of land area and agricultural production suggest adopting new technologies, implementing modern irrigation practices, and reducing cultivation in arid/desert regions to mitigate impending water shortages and subsidence.
کلیدواژهها [English]
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