Gully erosion is one of the main modes of slope erosion on the Loess Plateau, which plays a connecting role in the slope gully erosion system. The Loess Plateau has wide and densely distributed gullies. The study selected a typical small watershed in the hilly and gully region of the Loess Plateau to measure the morphological characteristics and spatial-temporal distribution of gullies. A deep learning image semantic segmentation model was used to identify and extract the morphological features of gullies at the watershed scale from 2009 to 2021 based on remote sensing images (0.5 m resolution) and then analyze their temporal and spatial distribution characteristics. The results revealed that: (1) most gullies occurred in the hilly southern parts of the watershed, which has complex landforms and large slope gradients; (2) gully number increased from 1,159 in 2009 to 2,312 in 2021 (average 97 per year), with a frequency development rate of 2.87 km –2 y –1; (3) gully length generally ranged from 25–40 m, with an average growth rate is 1.66 m y –1 and density development rate of 0.12 km km –2 y –1; (4) gully width ranged from 0.5–1.5 m, with an average growth rate of 0.04 m y –1. (5) the total gully area increased from 0.0566 km² in 2009 to 0.1072 km² in 2021, with a development rate of 4,213.39 m² y –1 and dissection degree development rate of 0.0125% y –1. This study provides a theoretical and scientific basis for gully erosion control and eco-environmental protection at the watershed scale on the Loess Plateau.

Extreme meteorological events occur frequently, and changes in the spatial pattern of land use have greatly affected the soil erosion process in the hilly and gully region of the Loess Plateau. As a typical governance watershed in the hilly and gully area of the Loess Plateau, the Jiuyuangou watershed has experienced significant changes in land use and land cover (LULCC) in the past ten years due to the conversion of farmland to forests, economic construction, and abandonment of cultivated land. However, the evolution process of soil erosion under LULCC in the watershed is unclear. This study uses satellite images to extract information on LULCC in the watershed and the Chinese soil loss equation (CSLE) model to evaluate the temporal and spatial evolution of soil erosion in the watershed from 2010 to 2020. The main results showed that: (1) The continuous vegetation restoration project in the watershed reduced soil erosion from 2010 to 2015; however, the frequency of extreme rainfall events after 2015 reduced its impact. The annual average soil erosion modulus decreased from 10.85 t ha –1 yr –1 in 2010 to 8.03 t ha –1 yr –1 in 2015, but then increased to 10.57 t ha –1 yr –1in 2020; (2) The main LULC type in the Jiuyuangou watershed is grassland, accounting for 62.23% of the total area of the watershed, followed by forest land (28.41%), cropland (6.77%), building (2.49%), and water (0.09%). The multi-year average soil erosion modulus for land use type is cropland > grassland > building > forest land; (3) Significant spatial correlations between soil erosion change and LULCC for common ‘no change’ and common ‘gain’ occurred in the settlements, roads, valleys, and areas near the human influences with good soil and water conservation, but not other regions due to the influence of climatic factors (heavy rain events). This study provides a scientific reference for planning and managing water and soil conservation and ecological environment construction in the basin.