An integrated modeling method for rainfall-induced geohazard chains: coupling landslide mobilization and flow-state transition

Extreme rainfall in mountain catchments can trigger shallow landslides, debris flows, and sediment-laden floods as interconnected geohazard chains. This study proposes a coupling-oriented modeling framework that links rainfall-induced landslide-source mobilization with downstream flow-state transition. Rather than introducing separate submodels, the main methodological contribution is to convert hydrologically activated slope instability into time-, geometry-, and volume-explicit sediment supply and to route this supply as a single evolving solid–water mixture for identifying slide-like, debris-flow-like, and flood-dominated pathways. The method was applied to the 2023 extreme rainfall event in Beijing, China. Hydrological benchmarking showed that the dynamic front–perched layer formulation better captured localized pressure-head development near landslide-prone locations than bucket-type storage and Green–Ampt infiltration. The cellular-automaton (CA)-based source module generated rainfall-aligned shallow landslide release areas with explicit timing, depth, and object-scale morphology. Downstream simulation showed that released material mainly formed short-lived, high-concentration pulses rather than a sustained debris-flow-dominated process. During the main rainfall stage, released landslide volume was approximately 3.29 × 10 4 m 3 , whereas additional scour contributed only approximately 7%. The event therefore followed a rapid-dilution pathway toward flood-dominated, sediment-laden transport.