Evaluating thresholds: the impact of terrain modifications on landslide susceptibility in a mountainous city

Terrain modifications from urban expansion significantly affect landslide susceptibility, particularly in mountainous regions where excavation disrupts slope stability. This study integrates the Earthwork Volume Index (EVI) into Environmental Impact Assessments (EIA) to evaluate terrain alterations in Busan, South Korea. By incorporating land-use data (2000, 2010, 2020), it captures long-term urbanization trends and their impact on slope stability, advancing beyond static susceptibility assessments. Using a Random Forest model (AUC: 0.906, RMSE: 0.368), the study quantifies the relationship between terrain modification and landslide susceptibility. The results indicate higher susceptibility in high-EVI, steeply sloped regions undergoing intensive development. Multi-collinearity analysis confirms key factors’ independent predictive contributions. This study advocates for EVI-based thresholds in EIAs as a quantitative risk assessment tool, offering a data-driven framework to balance urban expansion and disaster risk mitigation. The findings highlight the need to refine EVI criteria, expand landslide inventories, and integrate remote sensing for real-time monitoring, providing a scalable methodology for rapidly urbanizing, landslide-prone regions worldwide.