Figure 10(b) indicates that the sand peak was always behind the flood peak, both on 14 July 2000 and 21 August 1998. Generally, runoff erosion can be fully developed by the long runoff convergence time, the sediment carrying capacity increases with increased river flow, and peak values of sediment concentration often appear at the same time or lag behind the flood peak. However, on the loess hilly and gully region, as soil water content increases in the late period of runoff yield, the shear strength of loess decreases, runoff erosion increases, and gravity erosion also frequently occurs, which makes the probability of the sand peak lagging behind the flood peak increase. The results are consistent with Dugan et al. (2009) who demonstrated the importance of antecedent moisture condition as an important factor in the rainfall runoff and sediment transport response to precipitation events64. The fundamental cause of erosion changes lies in rainfall characteristics, the soil erosion quantity caused by high rainfall intensity at a certain stage of an event-based rainstorm accounted for most soil erosion65.