Sustainable land management for expressway slopes: a SHAP-based analysis of runoff and erosion trade-offs between natural and artificial slopes

Introduction The linear infrastructure of expressways greatly disturbs neighboring lands and creates slope systems that are fragile, but critical to environment management. Understanding the complex interactions between ecosystem disservices of surface runoff and soil erosion in slope systems is key for slope stability. However, the difference and associated drivers of the trade-offs on natural versus artificial slopes remain poorly understood. Method In this study, we addressed this gap by conducting a comparative analysis of the trade-offs between surface runoff and soil erosion on 250 natural and 194 artificial slopes at the Hekou section of the Xinhe expressway in Yunnan, China. We used root mean square error to quantify the trade-offs and applied the SHAPLE Additive exPlanations model to interpret the different contributions of environmental and management factors to the trade-offs. Results The results show that soil erosion is significantly higher on the artificial slopes compared to the natural slopes. The trade-off between soil erosion and surface runoff was stronger on natural slopes compared to the artificial slopes, suggesting a more complex nonlinear interaction between the two in natural slope systems. Precipitation is the main contributing factor, but its influence is in the opposite direction on the two types of slopes. Precipitation strengthens the trade-offs for natural slopes and weakens those for artificial slopes. This important finding suggests that anthropogenic interventions simplify the hydrological erosion response of artificial slopes, making them more linearly dependent on hydrodynamics. Similarly, elevation positively affects the natural slopes but negatively affects the artificial slopes. Increased normalized vegetation index enhanced the trade-off, while the implementation of soil and water conservation measures increased the complexity and intensity of the trade-off for the artificial slopes. Discussion This study demonstrates that land management measures can fundamentally alter the mechanisms underlying soil and water interactions in the slope systems. These findings provide a scientific basis for linear infrastructure projects to achieve sustainable land management.