## 4 Discussion  
### Rainfall Producing Yield Soil Sediment  
High soil water content increases sediment detachability by runoff shear forces and raindrop impact [19]. It is therefore because of the high initial soil moisture content that we observe soil erosion \begin{table}
\begin{tabular}{c c c c c c} \hline
**Label** & **Fitted Equation** & **SSE (m3)** & **\(R\)-Square** & **RMSE (m3)** & \(p\)**-Value** \\ \hline
1 & (ax + b\(y\)) + c & 0.0001378 & 0.7936 & 0.0007281 & \textless{}0.01 \\
2 & a(xy) + b & 0.0003277 & 0.9509 & 0.0003484 & \textless{}0.01 \\ \hline \end{tabular}
\end{table} 
Table 1: Fitted equations (\(x\) = rainfall duration \(>\) 0 min, \(y\) = rainfall intensity \(>\) 15 mm/h). Figure 10: Model performance: (**a**) measurement _versus_ prediction of the model (\(n\) = 29); (**b**) linear relationship between model and measurement (RMSE = 4.8) (\(n\) = 29). in the first minute of our experiments. In Figure 8a, p1 shows positive value indicating that saturated soil or runoff was produced. Since the strength of the soil is reduced, shearing the soil by surface water flow is easier. Figure 3 illustrates that the slope toe is more heavily eroded than other parts of the slope. The moisture content of soil in a particular area depends on the inflow and outflow of water. In Figure 8b, m1 at the top of the slope does not receive runoff from other parts of the slope and subsequently displays a slow increase in moisture content, consistent with the rainfall intensity increment (no more than 0.2%). Initial moisture could also affect the moisture content. When the initial soil moisture is low, water fills the soil pore space more quickly than it drains out (due to a high suction hold on the water). By contrast, in soil with high moisture content, the drainage rate is high and there is a balance between water inflow and outflow. As shown in Figure 8b,c, at m2 the moisture improves more than 0.5% compared to at m1.For one thing, it is likely due to runoff supply from the upper slope to the middle part of the slope. For another, since the water flows downward, the subsurface water flow from m1 to m2 can also increase the moisture of m2. High rainfall intensity and the subsequent increase in surface runoff increase the rate of soil erosion [3]. In our experiments, no eroded sediment is produced when the rainfall intensity is lower than 15 mm/h. Sediment yields are linked to transport and detachment capacity, which is the limiting factor of the erosion process. If the detachment capacity is significantly lower than the transport capacity, the process is referred to as \"detachment-limited erosion\" [20]. Materials are transported only after being detached; therefore, there must be a threshold rainfall amount at which soil erosion will begin. Indeed, several modeling studies observed that shearing force induced by runoff must overcome resistance in order to achieve soil loss [5; 21]. In Figure 9b the soil erosion rate increases with time (when the rainfall intensity is smaller than 50 mm/h; it decreases with time when the rainfall intensity is greater than 50 mm/h). In terms of rainfall intensity, the soil erosion rate in the first three minutes is greater than in the last three minutes. Decreasing soil erosion rates with time could be a result of the subsurface soil's appearance after the surface soil detachment. The previous subsurface becomes the new surface soil, which can store more water. Another important factor is the formation of concentrated flows; this increases erosion in the rills but reduces runoff from other parts, which may result in flows with high sediment concentration, close to the limit of transport capacity. Importantly, the cumulative rainfall is linearly related to the yield sediment volume, with high correlation (Table 1, label 2).