Rainfall Threshold Analysis for Various Geological Formations in Northeastern Guangdong, China: A Physically-Based Approach

Landslide occurrences are influenced by various spatial and climatic factors, some predictable to an extent while others remain uncertain. Physically-based models like TRIGRS are crucial for assessing slope stability and rainfall thresholds. In this study, we evaluated rainfall intensity (RI) and duration (RD) for landslide prediction in Guangdong's northern region, focusing on areas with historical high-intensity rainfall and landslides. Our study encompassed four rainfall intensities (1 mm to 50 mm) and 32 durations (1 to 72 hours), considering diverse hillslope gradients and geological formations (sedimentary and igneous rocks). Increasing RI correlated with decreasing RD until a threshold for slope failure was reached, defining spatial thresholds across varied rainfall simulations. Geological formations exhibited varying threshold intensities for slope failure, with igneous rock demonstrating greater resistance due to its granite and sandstone composition. Multiple calculations of the factor of safety for different intensities of rainfall events permitted the fitting of power-law equations to the critical intensity and rainfall durations for different grid cells. Simulation results indicated igneous rock failure after 4.3 hours of 50 mm/h rainfall, while sedimentary rock failure in low-strength areas within 2 to 3 hours with the same rainfall intensity at different locations. Validation with landslide data yielded accuracies of 67.42% for sedimentary rock, 68.13% for both sedimentary and igneous rock, and 63.51% for igneous rock alone using TRIGRS. This analysis highlights the geological role in slope failure and aids in future rainfall-based threshold evaluations for early landslide warnings.