Figure 8. Statistical
comparison of soil erosion by slope between previous study(Huang,2020)
and our study in 2015(a) Statistical correlation analysis of soil
erosion modulus by slope between the previous study(Huang,2020) and our
study in 2015(b).
Relationship between land use and soil
erosion
Our results showed that for the 2010–2020 LULCC, the multi-year average
soil erosion rate for different land uses significantly differed, with
cropland (55.1 t ha–1 yr–1)
> grassland (8.93 t ha–1yr–1) > building (1.6 t
ha–1 yr–1) > forest
land (1.65 t ha–1 yr–1), similar
to the findings of Zhao et al. (2022) and Han et al. (2020). The
‘Returning Farmland to Forest Project’ program implemented in 1999
significantly increased the vegetation coverage rate, increasing the
grassland and forestland area from 83.1% in 2010 to 90.7% in 2020. The
Loess Plateau has recently experienced large-scale cropland abandonment
due to rural population movements, cropland quality, and economic
benefits. At the end of 2016, a survey of 235 villages in China revealed
that 78.3% had abandoned up to 14.32% of their cultivated land. Soils
on plots with lower vegetation cover were being disturbed more
frequently and intensely by tillage, accelerating erosion (García-Ruiz,
2010; Zuazo and Pleguezuelo, 2009). The abandoned cultivated land
resulted in increased biocrust and vegetation cover in interplant
patches, increasing soil infiltration and reducing the generation of
erosive runoff (Chirino et al., 2006; Yuan et al., 2020), and the
vegetation root systems reduced soil erodibility, protecting the soil
from raindrop erosion and runoff transport (Chen et al., 2021; Chuenchum
et al., 2020). Therefore, soil erosion was curbed in the Jiuyuangou
watershed from 2010 to 2015.
However, the increase in forest/grassland area and vegetation coverage
from 2015 to 2020 increased the soil erosion rate in the watershed from
2015 to 2020, primarily due to more frequent extreme rainfall events
after 2015. The Loess Plateau has an extremely uneven distribution of
annual rainfall. The rainfall erosivity in the basin from June to
September in 2010, 2015, and 2020 accounted for 85%, 50%, and 88% of
annual rainfall erosivity, respectively. At the same time, frequent
heavy rainfall events occurred in the basin after 2015 (e.g., July 26,
2017 (212.2 mm), August 7, 2018 (151.3 mm), August 7, 2019 (150 mm), and
August 4–6, 2020 (80.3 mm)). Flooding season precipitation in the
Jiuyuangou watershed has become the main precipitation for the year,
with the erosion and sediment production caused by rainstorm erosion an
important feature of this area. It is far sufficient to rely on surface
micromorphological changes from vegetation restoration to manage
rainstorm erosion (Han et al., 2020; Yang et al., 2011). The current
land use distribution pattern in the hilly and gully region of the Loess
Plateau in northern Shaanxi cannot prevent soil erosion under extreme
rainstorm conditions. Optimizing the distribution of land use types in
the catchment area should be the focus of soil erosion control (Wang et
al., 2020). The frequent occurrence of extreme rainfall has affected the
consistency of soil erosion changes and LULCC, evidenced by large-scale
soil erosion losses in areas with no change in land use patterns. In the
northern part of the basin, far from human settlements and construction
land, land use and soil erosion followed a common ‘loss’ trend, ‘no
change’ occurred in settlements and construction land. The frequent
occurrence of extreme rainfall has affected the consistency of soil
erosion changes and LULCC, evidenced by large-scale soil erosion losses
in areas with no change in land use patterns. In the northern part of
the basin, far from human settlements and construction land, land use
and soil erosion followed a common ‘loss’ trend, ‘no change’ occurred in
settlements and construction land. Therefore, the LULCC and soil erosion
changes are spatially correlated in areas near the human activities or
settlements, roads, cropland, and valleys with good soil and water
conservation.