The unit hydrograph is an important method to analyse relationships between runoff and sediment yield of event-based rainstorms. Figure 10 shows two hourly flow-sediment hydrographs of Zhifanggou Watershed under typical rainstorm events. Figure 10(a) indicates that sediment concentrations increased along with increased flow rate during the water rising period, and the water flow fades away quickly and sediment concentration decays slowly. The results agree well with Cao et al. (2015) that the initial soil losses increased rapidly and reached the peak value nearly at the same time as the peak runoff in the Red Soil region of southern China, then soil loss decreased and runoff leveled out63. Generally, the typicality of rainstorm erosion in loess hilly region are mainly manifested in several stages: First, because of differences of soil and topography, overland flow is often collected together from sheet overland flow and small rill flow, and causes rill erosion. Second, with the continuity of the rainfall-runoff process, the small rill flow also gradually increases, it will form shallow gully, dissected valley, gully and gravity erosion on steep slopes before entering into large ditches or streams. Third, infiltration-excess runoff on slopes pours into dissected valleys through overflow, rill flow and shallow gully flow, and then flows into river tributaries, again by different levels of ditches. Fourth, due to runoff erosion, gravity erosion and the increased sediment carrying capacity, the sediment carrying flow increases sediment concentration with the rising of the channel water-level. However, the increased amplitude of sediment concentration does not often correspond to the increase in river flow, and the occurrence time of the flood peak is not always consistent with the sand peak31.Figure 10Flow and sediment hydrograph on (a) 14 July 2000 and (b) 21 August 1998.