Landslide‐Channel Coupling Controls Asymmetric Flash Flood—Debris Flow Transitions: Insights From an Extreme Rainfall‐Induced Hazard Chain in Yuzhong of China in 2025

Abstract Extreme rainfall‐triggered landslide–flash flood–debris flow hazard chains (LFFDF) are increasingly responsible for hydroclimatic losses worldwide. Although dynamics of individual hazards are established, transition mechanisms within LFFDF governed by coupled landslide–channel responses remain unresolved. Taking a catastrophic LFFDF event in northwestern China in 2025, we reconstructed the transition dynamics of the hazard chain using satellite data, seismic records, and numerical modeling. The results show that the LFFDF cascade operates as asymmetric transition processes, in which the dominant controls are state‐dependent. Rainfall‐induced landslides supplied one‐third of the mobilized sediment; their interaction with flash floods increased channel‐flow Shields stress by more than an order of magnitude, prematurely initiating debris flows in headwater channels. The downstream reversion from debris flow to flash flood is mainly controlled by the thickness and saturation state of channel sediments. Finally, we suggest a cascade‐based paradigm for risk assessment to enhance community resilience to LFFDF risks.