Results

Analysis of soil erosion factors

Rainfall, vegetation, and soil and water conservation engineering measures are the three major factors affecting soil erosion in the Loess Plateau. We analyzed the characteristics of erosion conditions in the watershed through temporal and spatial changes of erosion factors in the CSLE model. For this purpose, various soil erosion factors in the model were calculated and presented as a 10 m resolution grid map. The soil erodibility factor (K), slope length and slope factor (LS), and tillage measure factor (T) remained unchanged from 2010 to 2020 (Figure 2a-c), while the rainfall erodibility factor (R), vegetation cover measure factor (B), and soil and water conservation engineering measure factor (E) varied with year.
Figure 2d-f is the rainfall erosivity map of Jiuyuangou watershed in 2010, 2015, and 2020 In general, average annual rainfall erosivity from 2010 to 2020 first decreased and then increased. Spatially, the rainfall erosivity increases from the northeast of the watershed to the southwest of the watershed.Basin rainfall is concentrated from June to September but extremely uneven during the year and prone to rainstorm erosion.
Vegetation cover impacts soil erosion development by affecting surface runoff processes in the watershed. Figure 2g–i shows three-year vegetation coverage factors from 2010 to 2020. At the same time, areas with low B values increased from 75% in 2010 to 84% in 2020. The low B value area gradually expands from the northeastern part of the watershed to the southern residential area and agricultural land, representing better vegetation cover and lower erosion risk than the high B value area. Figure 2j–l shows that terraces and check dams are the main soil and water conservation engineering measures in the basin, and unique to the Loess Plateau. The area of terraced fields continued to decrease from 2010 to 2020, and the area of check dams increased from 2010 to 2015 and then decreased from 2015 to 2020. Since the project of returning farmland to forest commenced in 1999, the construction of check dams on the Loess Plateau started and continued until 2015, when the layout of the dam system was completed. Due to problems such as sediment deposition and poor management, the check dam area in 2020 was significantly less than 2015. Terraces are an important soil and water conservation measure in the basin, mostly horizontal terraces on ridges. During the study period, the area of terraced fields in the basin decreased year on year due to scour damage caused by rainfall and farmland abandonment. In 2020, the area of terraced fields had declined by 12.3% compared with 2010.