Vegetation pattern and topography determine erosion characteristics in a semi-arid sandstone hillslope-gully system

The hillslope-gully system serves as the primary contributor to both runoff and sediment yield. The WEPP (Water Erosion Prediction Project) model is often applied to investigate erosion characteristics at hillslope scale, demonstrating a high level of accuracy in simulating water erosion. In this study, according to in situ field monitoring (2014-2020) at a Pisha sandstone hillslope on the Loess Plateau, China, a total of 50 rainfall events' data were used as climatic data to calibrate the soil parameters, and 11 different vegetation patterns and four slope gradients of hillslope-gully systems were installed as inputs for the management and slope data, respectively. In systems A, B, C and D, the hillslope gradients were defined as 5 degrees, 8 degrees, 10 degrees and 12 degrees and the gully gradients as 15 degrees, 20 degrees, 25 degrees and 30 degrees, respectively. The results showed that the steeper the slope, the more severe the erosion. However, there was a critical value for the effect of slope on runoff. When the slope exceeded 8 degrees and the gully exceeded 20 degrees, the runoff no longer increased further and even decreased. The reduction in runoff in hillslope-gully systems was in the following order (in mm): system D (3.4 +/- 0.14) > system C (3.4 +/- 0.14) > system B (3.39 +/- 0.14) > system A (3.12 +/- 0.13). Increasing vegetation cover could reduce erosion. Differences in runoff between vegetation patterns were not significant (p > 0.05) and ranged from 8% to 26%. However, there were significant differences in the sediment yield reduction benefits of different vegetation patterns (p < 0.05), ranging from 17% to 66%. It was observed that vegetation located in the lower slope produced a more pronounced effect in mitigating sediment when the degree of cover was the same. We conclude that implementing watershed management strategies based on the vegetation and topographic attributes of hillslope-gully systems within the Loess Plateau, especially on Pisha sandstone hillslopes, serves as the fundamental approach to achieving sustainable watershed management.