Assessing critical soil moisture to demarcate terrain stability

Changes in rainfall patterns and the increased frequency of extreme rainfall events can significantly impact terrain stability in areas prone to rainfall-induced landslides. The spatial variability of terrain stability is closely related to the dynamics of soil moisture and the groundwater level, as both reflect the intensity and duration of precipitation events. Thus, soil moisture and groundwater level can effectively serve as proxies for assessing the stability of vulnerable terrains. Deriving critical maps of soil water content (SWC) for hazard initiation can significantly aid authorities, and emergency responders in risk management. Several studies have focused on delineating conditionally and unconditionally stable areas, in ‘partially saturated’ soils based on topography, mechanical properties, and a steady state wetness index (WI) or height of groundwater level (Montgomery and Dietrich, 1994). However, this approach does not account for the transient and unsaturated conditions of soils, both in the stability index and at the infiltration front (Lepore et al., 2013). To address this, the present study proposes a method for demarcating conditionally and unconditionally stable areas by incorporating both ‘unsaturated’ and ‘partially saturated’ conditions. Within the conditionally stable areas, we derive critical maps of landslide initiation.