Accelerated Gully Expansion in a Semi-Arid Watershed: A Multi-Temporal Analysis (1967–2024)

This study investigates the temporal dynamics, environmental controls, and morphometric characteristics of gully systems in the Jeyhoon watershed (southern Iran) over a 57-year period (1967–2024). Multi-temporal mapping was performed using aerial photographs, satellite imagery, and UAV-derived data, and gully expansion was quantified using multi-temporal change detection. Spatial overlay analysis was applied to assess relationships between gully development and environmental factors, including slope, land use, curve number (CN), and geology. Morphometric properties were derived from 481 cross-sections extracted from a high-resolution UAV-based DEM. Results show a significant increase in gully area from 133ha to 326ha (+146%), with expansion rates accelerating from 1.28 to 6.58 ha yr⁻¹. More than 96% of gullies occur on slopes below 2%, and 90–98% developed within rangelands. Gully expansion is strongly associated with moderate to high runoff potential (CN ≈ 68) and erodible lithology. Morphometric analysis indicates predominantly shallow but laterally expanded gullies, with high width-to-depth ratios, confirming the dominance of lateral erosion processes. Overall, gully evolution is primarily controlled by hydrological conditions and land surface characteristics rather than slope.