4. Discussion
This study combined remote sensing imagery and the SegNet model to analyze the morphological features of temporal and spatial distribution law in gullies at a watershed scale. Jiang et al. (1999) analyzed the distribution characteristics of gullies using W-B aerial photographs to identify 4,495 gullies in the Zhoutungou watershed in 1999. We found that the number of gullies in the watershed decreased sharply from 4,495 in 1999 to 1,153 in 2009 (Fig. 7) due to China’s returning farmland to forest project that has significantly improved vegetation coverage on the Loess Plateau and reduced the occurrence of slope soil erosion (Chenet al. , 2019; Dou et al. , 2020; Liang et al. , 2019), inhibiting the formation and development of slope gullies. However, the number of gullies increased slightly after 2009 due to (1) extreme rainfall on the Loess Plateau, increasing soil erosion (Huet al. , 2019; Li et al. , 2022; Wang et al. , 2020a; Zhao et al. , 2021); (2) the gully land consolidation project implemented in 2011 increasing the cultivated land area and, despite reducing watershed erosion to a certain extent (Chen et al. , 2020; Han et al. , 2018; Kang et al. , 2021b; Li et al. , 2016; Zhao, 2014; Zhao et al. , 2019), its associated engineering involving topsoil stripping and ridge construction has damaged the slope vegetation (increased slope) and soil environment (loosened soil structure), forming new gullies on the slope; (3) returning farmland to forest on the Loess Plateau has resulted in lush vegetation, making it difficult to see some gullies in the remote sensing images. Soil erosion on the Loess Plateau will gradually decline to achieve the strategic goal of protecting and controlling the ecological environment of the Loess Plateau, and ‘green water and green mountains are golden mountains and silver mountains’.