Figure 4. Recognition results of the SegNet model in the Zhoutungou watershed in 2021. Ephemeral gully recognition results at (a) the watershed scale and (b) the sampling area.
The SegNet model extracted 1,153, 2,045, 2,413, and 2,312 ephemeral gullies encompassing 34.32, 60.86, 71.82, and 68.81 km2 in 2009, 2012, 2018, and 2021, respectively, with a frequency development rate of 2.87 km2y–1 (Table 2). Most of the ephemeral gullies were in the southern half of the Zhoutungou watershed (Fig. 5), which has complex landforms and large slope gradients. From 2009 to 2012, many new ephemeral gullies formed in the northeast and south of the watershed, but some disappeared. From 2012 to 2018, new ephemeral gullies formed in the middle south and southeast regions of the watershed, while others disappeared in the northeast and southwest regions. From 2018 to 2021, only a few regions formed new ephemeral gullies, with many disappearing in the western region.
Table 2 Statistical characteristics for ephemeral gully number and frequency in the Zhoutungou watershed from 2009–2021.