Interpretable Landslide Susceptibility Mapping in Pacitan, Indonesia Using Bayesian-Optimized XGBoost and SHAP Analysis

Background: Landslide susceptibility mapping is essential in areas with complex topographic and geological conditions, such as Pacitan Regency, Indonesia, to identify landslide-prone areas and assess the factors influencing landslide susceptibility. Objective: This study developed a landslide susceptibility mapping model using Extreme Gradient Boosting (XGBoost), optimized through Bayesian optimization and interpreted using the SHapley Additive exPlanations (SHAP) method. Methods: The dataset consisted of 1,486 samples, comprising 743 landslide occurrence points and 743 non-landslide points. Eleven landslide conditioning factors were used as predictor variables: elevation, aspect, slope, geology, land use, profile curvature, plan curvature, distance to roads, distance to rivers, Stream Power Index (SPI), and Topographic Wetness Index (TWI). Model hyperparameter optimization was performed using Bayesian optimization with a Tree-structured Parzen Estimator (TPE). Results: The optimized XGBoost model achieved an accuracy of 69.80%, a precision of 70.34%, a recall of 68.46%, an F1 score of 69.39%, and a receiver operating characteristic area under the curve (ROC-AUC) of 0.7564 on the independent test set. The resulting susceptibility map classified the study area into five categories: very low, low, moderate, high, and very high susceptibility. SHAP analysis identified slope, aspect, plan curvature, geology, and distance to roads as the dominant factors influencing model predictions. Conclusion: Integrating Bayesian optimization, XGBoost, and SHAP provides an interpretable approach to landslide susceptibility mapping in Pacitan Regency. The resulting susceptibility map and feature-level explanations can support preliminary disaster risk assessment and spatial planning. However, residual classification errors and limitations associated with the use of static environmental predictors should be considered when interpreting the results.