Figure 5. Soil erosion modulus of LULC in Jiuyuangou watershed in 2010, 2015, and 2020
Grassland composed of small vegetation such as different low canopy and grass and forest land composed of tall trees and shrubs have different contributions in protecting soil from root erosion and reducing the erosion of topsoil by rainfall through canopy coverage. At the same time, the dead plants also increased the content of soil organic matter and the water holding capacity of soil after falling to the ground. so, in the past 10 years (2010–2020), the soil loss of grassland decreased by 0.51 t ha–1 yr–1, however, the soil loss of forestland increased by 1.84 t ha–1yr–1.
Figure 6 shows the area statistics for land use type and soil erosion grade in the Jiuyuangou watershed in 2010, 2015, and 2020. Changes in the building area due to human activities had little effect on serious soil erosion, with the predominantly weak erosion decreasing from 365.01 ha in 2010 to 161.89 ha in 2020. Similarly, forest land mainly had weak erosion (94.7%-98.8%), decreasing from 2144.43 ha in 2010 to 1863.68 ha in 2020. Cropland mostly had weak, slight, and moderate erosion. From 2010 to 2020, The area of three kinds of soil erosion in cropland decreased. Considering that grassland occupies the vast majority of the watershed area, it comprises all soil erosion grades, predominantly weak (65.4%-72.7%) and slight (16.9%-22.15%%) erosion. Different from cropland, weak erosion in grassland increased from 2355.68 ha to 3149.54 ha and slight erosion decreased from 797.92 ha to 733.60 ha.