Introduction:

Sand dunes, especially barchan dunes, represent some of the most visually striking and dynamically responsive landforms in Earth’s arid and semi-arid landscapes. Characterized by their crescentic shape, sharp horns, and steep slip faces, barchan dunes form under conditions of limited sand supply and unidirectional wind regimes. Their mobility and morphological plasticity make them sensitive indicators of environmental change, serving as natural recorders of wind patterns, sediment availability, and surface roughness. In regions such as the Kalateh Mazinan area in northeastern Iran — situated within the expansive arid belt of Razavi Khorasan Province — barchan dunes are not merely passive features but active agents of landscape transformation. Monitoring their behavior is critical not only for advancing fundamental geomorphological knowledge but also for practical applications including desertification control, infrastructure planning, agricultural zoning, and ecological conservation.

Despite their significance, comprehensive, high-resolution spatiotemporal analyses of barchan dune dynamics in Iran — and particularly in the Kalateh Mazinan region — remain scarce. Most previous studies have relied on coarse-resolution satellite imagery or infrequent field surveys, which often fail to capture the subtle yet critical micro-scale changes in dune morphology and position. This study addresses this gap by employing cutting-edge unmanned aerial vehicle (UAV) photogrammetry to generate precise, time-series digital elevation models (DEMs) and orthophotos, enabling detailed quantification of dune migration and structural evolution over a 29-month interval (May 2022 to October 2024).



Materials and Methods:

The methodological framework of this research integrates advanced remote sensing techniques with classical geomorphometric analysis. Two high-resolution aerial surveys were conducted using a DJI Phantom 4 Pro drone, capturing overlapping nadir and oblique imagery under optimal lighting and wind conditions to minimize motion blur and shadowing. The imagery was processed using industry-standard photogrammetric software — Agisoft Metashape and Pix4Dmapper — to reconstruct 3D point clouds, orthomosaics, and DEMs with centimeter-level accuracy. Five morphologically distinct barchan dunes were selected as representative samples based on their spatial distribution, isolation from neighboring features, and clarity of form. For each dune, a suite of 12 quantitative parameters was extracted: planimetric area, perimeter, mean and maximum elevation, volume, windward and leeward slope angles, lengths of both horns (arms), inter-arm width, and crestline orientation. Crucially, displacement was measured by tracking three fiducial points — the tips of the windward and leeward arms, and the apex of the crest — across the two epochs. The arithmetic mean of these three displacement vectors was taken as the representative migration distance for each dune.



Results:

Results indicate a wide spectrum of dune mobility and morphological response. Total displacement ranged from 9.47 meters (Dune 5) to 27.76 meters (Dune 4), yielding a regional average migration rate of 20.57 meters over the study period — equivalent to approximately 8.5 meters per year. Dunes 1, 2, and 3 exhibited moderate volumetric growth (ranging from +3% to +7%) and elongation along the dominant northwest–southeast axis, suggesting sediment accumulation and forward propagation under consistent wind forcing. Dune 4, the most mobile feature, displayed morphological signs of coalescence with a neighboring dune, including flattening of the inter-dune depression and merging of slip faces — a phenomenon indicative of dune field maturation and potential transition toward transverse or barchanoid ridge forms. In contrast, Dune 5 remained relatively static, with minimal displacement and unchanged volume, possibly due to local topographic sheltering, higher soil moisture retention, or the presence of sparse vegetation anchoring the surface sediment.

Correlation analysis revealed that displacement rate was positively associated with initial dune volume and windward arm length in three of the five dunes, aligning with theoretical models that link dune size to mobility under constant wind stress. However, Dune 5’s anomalous behavior — large size yet low mobility — underscores the influence of localized environmental controls, such as microtopography, sediment cohesion, or anthropogenic barriers. Slope asymmetry (steeper leeward faces) was consistent across all dunes and aligned with the regional wind regime, further validating the unidirectionality of aeolian transport in the study area.



Discussion:

The discussion contextualizes these findings within broader aeolian geomorphology literature. The observed migration rates fall within the expected range for mid-latitude desert dunes under moderate wind regimes (cf. Baddock et al., 2011; Zhang et al., 2020). The detection of dune merging processes adds empirical support to conceptual models of dune field evolution, wherein isolated barchans progressively interact, coalesce, and reorganize into more complex morphologies. Methodologically, this study demonstrates that UAV-based photogrammetry offers unparalleled spatial and temporal resolution compared to traditional techniques, enabling detection of sub-meter-scale changes and facilitating process-based interpretation rather than mere descriptive mapping.



Conclusion:

In conclusion, this research provides a robust, replicable framework for monitoring barchan dune dynamics using low-cost, high-efficiency UAV platforms. The findings confirm the dominant control of regional wind patterns on dune form and migration in Kalateh Mazinan, while also highlighting the modulating role of local factors. These insights are vital for predictive modeling of desert landscape evolution and for designing targeted interventions to mitigate dune encroachment on human settlements and agricultural lands. Future research should expand the temporal scope of monitoring, integrate in-situ meteorological data (particularly wind speed and direction), and explore seasonal variations in dune activity to build more comprehensive predictive models under scenarios of climatic variability and land-use change.