Response of runoff-sediment processes to vegetation restoration patterns under different rainfall regimes on the Loess Plateau

Vegetation restoration dominates the changes of land surface and then results in the reduction of runoff and sediment yield within a catchment. This study investigated the responses of runoff and sediment yield to vegetation restoration patterns under different rainfall regimes in the paired catchments: Yangjiagou (0.87 km2) with afforestation restoration (Y-AR) and Dongzhuanggou (1.15 km2) with natural restoration (D-NR) on the Loess Plateau. A total of 133 and 164 measured flood events, respectively, were selected to access this investigation in the two catchments during 1954-1965 and 2005-2017. Compared with natural restoration, the benefits of annual runoff and sediment reduction by afforestation reached 60.4 % and 75.1 %, and the high-flow events (peak discharge: 0.1-27.1 m3/s) reduced by 78 %. The 190 erosive rainfall events were categorized into three rainfall regimes, including long-duration and low-intensity (LDLI), short-duration and heavy-intensity (SDHI), short-duration and low-intensity (SDLI). Under each rainfall regime, the flood events in the D-NR had sharply risen with high discharge and sediment peaks, whereas the events had relatively flattened hydrographs and sedigraphs with low peaks in the Y-AR. Hysteresis analysis suggested that anticlockwise and eight-shaped (or more complex) anticlockwise loops were the dominant types in the Y-AR and D-NR, respectively. The power regression model indicated good relationships for rainfall-runoff and rainfall-sediment under regimes LDLI and SDHI in the Y-AR, whereas it was slightly worse in the D-NR. By contrast, afforestation significantly reduced discharge peak and maximum suspended sediment concentration of SDLI events by 59.6 % and 46 %, respectively. Afforestation played a critical role in the difference in runoff-sediment yield processes between the two restoration patterns through the direct vegetation cover and increased ET (evapotranspiration) and soil properties changes. The findings could provide valuable insights on hydrological responses to different vegetation restoration patterns and improve the understanding for watershed management on the Loess Plateau.