Physically-based rainfall-induced landslide thresholds for the Tianshui area of Loess Plateau, China by TRIGRS model

Physically-based models are widely recognized as valuable tools for analyzing slope stability and determining rainfall thresholds for landslides. In this study, a MATLAB program that utilizes the physically-based TRIGRS model to define rainfall intensity and duration thresholds is presented in the loess watershed basin of the Tianshui area, Gansu Province, China. We calculated the critical rainfall intensity (Ic) and duration conditions (D) that predict failure in each grid cell of 21 different rainfall intensity scenarios ranging from 1 mm/h to 100 mm/h and then fitted equation parameters (scale parameter α and shape parameter β) of the threshold curves by power-law equations. By considering the equation parameters within different hillslope gradient ranges, the rainfall threshold curves accounting for geological and geomorphological factors are ultimately established for the loess area. Our findings reveal a negative correlation between the scale parameter α and the shape parameter β. As α increases, β decreases until a specific threshold value of α is reached, at which β remains constant. A significant impact of hillslope gradient conditions on the shape of the threshold curves is observed. As the hillslope gradient increases, the equation parameters decrease. Furthermore, the position of the rainfall threshold exhibits considerable variation with respect to different lithological types. This analysis may help more deeply understand the different factors affecting the physically-based threshold variability, and the threshold curves can be a good alternative for performing the early warning of rainfall-induced landslides in loess areas.