5. Conclusion
In this study, the SegNet model was used to recognize gullies and extract their morphological features at a watershed scale from 2009 to 2021 to analyze the temporal and spatial distribution and evolution law of gullies. The number of gullies increased by 1,159 from 2009 to 2021 (average 97 per year), with a frequency development rate of 2.87 km2 y–1, mainly in the hilly southern part of the watershed, with complex landforms and large slope gradients. Gully lengths ranged from 5 to 230 m (average 48.39 m), with an average growth rate of 1.66 m y–1 and density development rate of 0.12 km km² y–1. More than 99% of the gullies are 0.5–1.5 m wide, with an average growth rate of 0.04 m year-1. The total gully area increased from 0.0566 km² in 2009 to 0.1072 km² in 2021, with a total area development rate of 4,213.39 m² y–1 and dissection degree development rate of 0.0125% y–1. Future soil erosion control should strengthen the erosion strategy caused by extreme rainfall events. Persisting with the returning farmland to forest project should realize ecological environmental protection of the Loess Plateau, and the strategic goal of ‘green water and green mountain is golden mountain and silver mountain’.