(c) Length variation from 2012–2018 (d) Length variation from 2018–2021
Figure 5. Length spatial-temporal evolution of gullies from 2009 to 2021
3.2.3 Width of gullies
From 2009 to 2021, gully width ranged from 0.5 to 2.5 m, with more than 99% between 0.5 and 1.5 m (Fig. 6a). The proportion of gully widths 2.0–2.5 m decreased from 0.67% in 2009 to 0.05% in 2021. From 2009 to 2021, the gullies had an average width development rate of 0.04 m y–1.
From 2009 to 2012, 63.73% of gullies increased in width, 18.81% decreased, and 17.47% did not change, with about 32% changing by 0–0.2 m and about 41% changing by 1–1.2 m (Fig. 6b). From 2012 to 2018, 29.14% of gullies increased in width, 19.84% decreased, 51.02% did not change, with about 61% changing by 0–0.2 m (Fig. 6c). From 2018 to 2021, 17% of gullies increased in width, 12.21% decreased, and 70.79% did not change, with more than 86% changing by 0–0.2 m (Fig. 6d). The average width variation range of gullies gradually decreased from 2009 to 2021.