ارزیابی روند بیابان‌زایی با استفاده از شاخص‌های پوشش گیاهی و تغییرات ضریب آلبدو در دوره زمانی 2000-2023، مطالعه موردی: حوضه آبریز مند در جنوب غرب ایران

ABSTRACT
Desertification is one of the most significant land degradation processes in arid and semi-arid regions, driven by both natural and anthropogenic factors. This study aims to assess desertification trends and environmental changes in the Mand basin using remote sensing techniques and spatiotemporal analyses over three time periods as 2000, 2013, and 2023. Satellite-derived vegetation indices, including NDVI (Normalized Difference Vegetation Index), EVI (Enhanced Vegetation Index), SAVI (Soil Adjusted Vegetation Index), LAI (Leaf Area Index), VCI (Vegetation Condition Index), LST (Land Surface Temperature), and albedo, were employed to monitor ecological shifts. LAI and SAVI also demonstrated decreasing tendencies, reflecting vegetation loss and soil exposure. In contrast, the EVI slightly increased during the same period, possibly due to changes in land management practices or vegetation types. Albedo values revealed a fluctuating but meaningful trend; in 2000 (mean = 0.2378, SD = 0.0461), in 2013 (mean = 0.2343, SD = 0.0647), and in 2023 (mean = 0.2271, SD = 0.0389). Despite a temporary increase in 2013 (up to 0.4345), the overall decrease in albedo suggests progressive soil degradation and expansion of bare surfaces, reinforcing the desertification process. Regional analysis revealed that central and southern parts of the basin experienced the most severe degradation, with increasing bare soil surfaces and declining vegetation cover. Based on albedo thresholds, the basin was classified into three desertification risk zones: low risk (20%); albedo > 0.4, moderate risk (50%); albedo 0.2–0.4, and high risk (30%); albedo<0.2. Statistical correlation analysis confirmed a strong positive relationship between NDVI and LAI (r=0.85, p < 0.01), while a robust negative correlation between albedo and vegetation indices supported the hypothesis of ongoing desertification. Findings highlight the need for sustainable land management policies, vegetation restoration programs, and continuous monitoring using remote sensing technologies to mitigate further desertification and ensure long-term ecological stability.
Extended Abstract
Introduction
Desertification is one of the most important land degradation processes in arid and semi-arid regions of the world, which occurs under the influence of natural and human factors. This phenomenon means the reduction or loss of the biological capacity of soil and vegetation, which can lead to significant changes in ecosystem functioning, a decrease in biodiversity, and an increase in environmental poverty. Desertification has significant impacts on natural resources, water security, soil health, and ecosystem resilience. Driven by land mismanagement, human activities, climate change, and frequent droughts, desertification accelerates ecosystem degradation. Advanced remote sensing technologies offer powerful tools for continuous environmental monitoring, enabling a thorough understanding of desertification processes. Soil indices such as albedo, LAI, and VCI also play an important role in detecting soil surface changes and desertification trends. Zhu et al. (2020) investigated desertification in Minqing County, northeast China, using Landsat images from 1978 to 2017 and the EVI index. The results of this study showed that vegetation cover and greenness increased over 31 years. Although several studies on desertification have been conducted using remote sensing technologies, there is still a need for comprehensive and area-based assessments in sensitive areas with high land use changes. This study aims to identify the desertification trend in the period 2000-2023 in the Mand basin in southwestern Iran using vegetation indices (NDVI, EVI, SAVI), soil indices (albedo, LAI, VCI). This study, using remote sensing data, multiple environmental indicators, and spatiotemporal analyses, has a special place in the existing literature. The main goal of this research is to accurately assess the desertification process, identify the relationships between the effective variables, and provide the necessary context for sustainable management of vulnerable areas.
 
 
Methodology
This research employs a regional and temporal analysis approach based on satellite data for three key periods as 2000, 2013, and 2023. After preprocessing and geometric correction, the images were analyzed using GIS and remote sensing software. Vegetation indices such as NDVI, EVI, and SAVI were employed to evaluate vegetation health, while soil and environmental condition indicators like albedo, LAI, and VCI provided insights into soil dryness and overall ecosystem vitality. Correlation and regression analyses elucidated relationships among these variables across time. Spatial maps were generated to illustrate desertification development and land degradation patterns within the region. In this study, all spatial indices were extracted based on Landsat 5 and 8 satellite data, after loading them into Google Earth Engine (GEE). After loading the images, cloud and noise filtering, cropping based on the study area, and data purification were performed to obtain high-quality and reliable data.
 
Results and discussion
The results demonstrate that the area has experienced a substantial expansion of degraded and decertified zones, with approximately 35% of the region affected by desertification indicators by 2023. Key vegetation indices have declined significantly, and the correlation analysis confirms the intensification of land degradation over time. Recurring droughts, water resource depletion, and human activities such as overgrazing and improper agricultural practices primarily drive these patterns. The strong relationships between soil and vegetation degradation emphasize the urgency of adopting integrated land management strategies, soil stabilization, reforestation, and water conservation measures to halt and reverse desertification trends. This authoritative and comprehensive study, using multi-attribute analyses and intertemporal data, showed that the study area has been facing a significant trend of vegetation degradation and desertification in recent decades. The continuous decrease in NDVI, EVI, and SAVI indices and the simultaneous increase in albedo index, as desertification indices, confirm the intensification of desertification processes and the degradation of ecological structures and soil. This trend, along with the strong and significant negative relationships between vegetation indices and dryland and desert soil indices, further highlights the importance of continuous monitoring and management interventions.
 
Conclusion
This study confirms that satellite-based remote sensing provides critical insights into desertification dynamics, offering valuable tools for early detection and policy formulation. The findings highlight the importance of sustained environmental monitoring, community engagement, and policy interventions to combat land degradation. By integrating technological approaches with sustainable land use policies, it is possible to restore ecological balance, enhance resilience to climate variability, and secure natural resources for future generations. The insights gained here contribute meaningfully to regional efforts for desertification control and sustainable environmental stewardship.
 
Funding
There is no funding support.
 
Authors’ Contribution
Authors contributed equally to the conceptualization and writing of the article. All of the authors approved the content of the manuscript and agreed on all aspects of the work declaration of competing interest none.
 
Conflict of Interest
Authors declared no conflict of interest.
 
Acknowledgments
 We are grateful to all the scientific consultants of this paper.