Runoff generation and erosion processes at the rock–soil interface of outcrops with a concave surface in a rocky desertification area

•Runoff generation at RSI changes distribution of surface and subsurface runoffs and sediments.•Rainfall–runoff primarily yields in form of surface runoff for vertical rock surfaces.•Maximal RSI runoff yield occurs at inclination angle of rock surface of 60°.•Proportion of non–RSI runoff to the total dominates the largest for incline rock surfaces.•Total soil loss is the smallest at inclination angle of rock surface of less than 45°. Rock surface flow, originating from outcrop surfaces during rainfall, represents a distinctive form of runoff influencing surface erosion and subsurface soil leakage in karst rocky desertification areas. Despite their significance, the processes governing runoff generation and erosion at the rock–soil interface (RSI) under the influence of rock surface flow remain poorly understood. This study aims to elucidate the generation and transformation of runoff at the RSI, along with their scouring erosion effects influenced by rock surface flow from concave-shaped outcrops. Artificial rainfall experiments were conducted on simulated rock–soil structural units featuring exposed rock surfaces and unexposed RSIs of outcrops with concave shapes. Two driving factors, namely rainfall intensity (R) and the inclination of the rock surface (IRS), were manipulated to investigate the formation and output processes of runoffs and sediments from the surface, RSI, and non-RSI (a site away from the RSI). The presence of an exposed rock surface altered the distribution pattern of rainfall–infiltration–runoff. An increase in the IRS led to a significant decrease in surface runoff (p