Effect of rock exposure on runoff and sediment on karst slopes under erosive rainfall conditions

Study region: Guizhou Province, Southwest China Study focus: Karst slopes are highly heterogeneous, with a large number of rocks exposed on the surface. Empirical soil erosion models (such as the revised universal soil loss equation (RUSLE)) based on homogeneous soil areas have encountered significant challenges in their application to karst areas. Currently, a quantitative relationship between the exposed rock and soil erosion has not been systematically established, although the establishment of this relationship could provide opportunities for empirical soil erosion model optimisation in karst areas. In view of this, we combined a field natural rainfall test with an indoor simulated rainfall test and artificially simulated exposed rock to investigate rock exposure rate (RER) effects on soil loss and runoff processes on karst slopes and attempted to build a coupled RER and soil loss model. New hydrological insights for the region: As the RER increased, the runoff and sediment content decreased under both simulated and natural rainfall conditions. Soil loss decreased exponentially with an increase in RER under natural rainfall tests in the field. There was a relationship between the soil loss and the RER quadratic function under simulated rainfall tests indoors. The exponential relationship based on natural rainfall more accurately reflected karst slope soil erosion conditions. These results contribute to a deeper understanding of soil erosion mechanisms on slopes in karst areas and provide confidence in our subsequent introduction of soil erosion sensitivity-exposed rock relationships to optimise soil erosion models such as RUSLE.