Soil loss and runoff characteristics in response to varying underground fissure ratios on karst slopes with thin soil layers in Southwest China

Karst slopes with thin soil layers, southwest China. Bedrock fissures can reallocate runoff and soil losses on karst slopes. However, the response of soil loss and runoff characteristics to bedrock surface fissure to the bedrock surface area ratio (RUF) on karst slopes with thin soil layers remain unclear. This study assesses the runoff and soil loss characteristics on karst slopes with a thin soil layer under five RUF scenarios (0, 1, 2, 3, and 4 %), a single rainfall intensity of 1.0 mm min −1 , and three slope gradients (10°, 15°, and 20°) through laboratory simulations. The highest surface runoff rate was observed under the 0 % RUF scenario at all slopes. Whereas the highest fissure runoff rate was found under the 4 % RUF scenario at the 15° slope. In contrast, the highest surface soil loss rates were found under the 1, 2, and 0 % RUF scenarios at the 10°, 15°, and 20° slope, respectively. The 2 % RUF scenario exhibited a significantly higher underground soil leakage loss rate at the 10° slope than that under other simulation scenarios. The surface runoff-to-total runoff and surface soil loss-to-total soil loss ratios under different scenarios ranged from 45.4 % to 78.3 % and 86.5–96 %, respectively. These results underscore that RUF redirects runoff, thereby modifying surface soil and leakage losses on karst slopes. • Relatively lower surface soil loss and runoff are observed under high RUF scenario. • Surface runoff occupies 45.4–78.3 % of the total runoff under various RUF scenarios. • Surface soil loss explains 86.5–96 % of the total soil loss for all RUF scenarios. • Bedrock fissures reallocate runoff to alter the surface soil and leakage losses.