Quantifying permanent gully erosion: Spatial patterns, volume estimation, and morphological dynamics in the loess hilly and gully region of China

Abstract

Permanent gully erosion is a significant contribute to land degradation, adversely affecting agricultural productivity and ecological integrity, which in turn poses a threat to regional environmental security and sustainable development. Accurate estimation of permanent gully erosion volumes and delineation of permanent gully morphological characteristics and spatial distribution patterns are crucial for developing targeted mitigation measures. This study integrates low-altitude unmanned aerial vehicle (UAV) photogrammetry and remote sensing imagery to construct a permanent gully volume model ($V=0.1215A^{1.4395}$) in the loess hilly-gully region of China. The application of the Boosted Regression Trees model for threshold segmentation based on length–width ratios further enhanced the model’s accuracy (R² = 0.9471, NSE = 0.9377). This study extracted the morphological parameters of 2,266 permanent gullies and found that their perimeters, areas, volumes, lengths, and widths ranged from 53.75 to 4,407.27 m, 12.94–5.49 × 10⁴ m², 96.39–1.08 × 10⁶ m³, 16.73–629.37 m, and 3.72–130.24 m, respectively. Significant spatial variability in the distribution of permanent gullies was observed, with the most severe erosion concentrated in the central and northern areas, where gully densities exceeded 3 km km⁻² (accounting for 24.82 % of the study area) and volumes surpassed 5 × 10⁵ m³ (accounting for 37.77 % of the study area). These areas are characterized by significant topographic relief, high rainfall intensity, and low vegetation cover. This research establishes a comprehensive framework for assessing permanent gully erosion volumes in the loess hilly-gully region and offers essential scientific evidence for the development of effective soil conservation and land management strategies in this vulnerable area. The findings are crucial for advancing sustainable development and enhancing ecological security in regions prone to severe gully erosion.