Hydro-Geotechnical Modelling and 45-Year Trends of Rainfall-Induced Slope Failures in Tropical Regions

Abstract

Global climate change is altering rainfall patterns and increasing the risk of landslides, prompting this study to investigate slope stability and responses through an integrated hydrological, statistical, and geotechnical framework. A 45-year dataset from 29 rainfall stations in Pacitan, East Java, Indonesia, was analyzed using statistical distributions to identify trends and predict extreme rainfall intensities for 5 to 100-year return periods. The results showed the existence of a localized increase in rainfall intensity exhibiting the most significant rise by reaching a predicted 50-year maximum of 416 mm. Subsequent numerical modeling was applied to evaluate slope safety factors (SF) under different rainfall scenarios and soil drainage conditions. The results showed that soil drainage capacity was the most important factor controlling slope stability. Poor drainage conditions characterized by low hydraulic conductivity at 10⁻⁶ m/s led to a drastic reduction in the SF and triggered instability during extreme short-duration or prolonged rainfall events. In contrast, slopes with good drainage maintained stable SF values of 1.5–1.8. This study concluded that inadequate drainage significantly amplified slope vulnerability to provide a critical basis for targeted landslide mitigation strategies in tropical regions under a changing climate.