## 5 Discussion
### Influence of Coal Mining Subsidence on Soil Erosion
However, [PERSON] [67] found that the slope length below 1 m has the effect of increasing soil erosion intensity through the rainfall erosion test of the plot below 10 m and the WEPP mill erosion model. However, with the increase in slope length, the energy of slope flow decreases, which leads to a decrease in soil erosion intensity. Based on the data of soil and water conservation monitoring points in Shiqiao small watershed, [PERSON] et al. [68] studied the effect of slope length on soil erosion in karst slope farmland. The study showed that the soil erosion modulus increased with the increase in slope length when the rainfall was greater than 30 mm, and the soil erosion modulus increased sharply and then decreased with the increase in slope length when the rainfall was less than 30 mm. [PERSON] et al. [69] quantitatively analyzed the soil erosion status of Baiquan County by using the Chinese soil loss equation CSLE. The study found that with the increase in slope length, the soil erosion modulus generally showed a trend of increasing first and then decreasing, and the slope length of 100-200 m contributed the most to erosion. The above research results are basically consistent with the research results in this paper, which show that the decrease in the slope length of the surface loess slope caused by coal mining subsidence affects the increase in the slope soil erosion modulus. More interestingly, the effect of slope length reduction caused by coal mining subsidence on soil erosion under the annual erosive rainfall scale and the typical field erosive rainfall scale is manifested as a mitigation effect and an aggra effect, respectively, and these two effects are mainly concentrated on the loess slope with a natural slope of 15-25\({}^{\circ}\). This enriches and deepens the scientific understanding of the soil erosion effect caused by the change in slope length of the surface loess slope in the coal mining subsidence area. Although this study provides valuable insights into the effects of coal mining subsidence on loess slope morphology and soil erosion, there are still some aspects worthy of further exploration in the future. First of all, this study focuses on the law of action in the process of mining subsidence and fails to obtain sufficient measured data for verification. In the future, the research will strengthen the collection of field data, especially in the field survey and soil erosion monitoring in the mining subsidence area, to further verify the prediction results of the model. Secondly, the numerical model used in the study is based on certain assumptions, such as soil uniformity and linear physical properties. However, the actual soil may have complex nonlinear and heterogeneous characteristics, which may affect the simulation results. Future studies can consider using more complex models and incorporating more changes in geological and soil properties to improve the accuracy and reliability of simulations. Finally, this study mainly focuses on the immediate or short-term impact of coal mining subsidence. This is based on the fact that high-intensity underground coal mining can cause a large-scale rock movement in the subsidence area in a short period of time and spread to the surface, significantly changing the original topography (the shape of the surface slope), which in turn has a profound impact on the characteristics and basic laws of soil erosion on the slope of the subsidence area. The coal mining subsidence in the Yellow River Basin generally takes 3-6 months from occurrence to basic stability, and it can reach complete stability in about 12 months. In such a short period of time, soil erosion factors such as precipitation and soil and water conservation measures will not change significantly. Although soil erosion factors such as soil and vegetation will deteriorate to a certain extent under the significant change in topographic factors, the impact on soil erosion will take a long time to appear.