The catastrophic debris flow in the Qinling Mountains of Xi’an, Shaanxi province, China, from 11 August 2023

Neglecting terrain-induced channel aggradation can lead to severe consequences, including greater economic losses and higher casualties. On 11 August 2023, a catastrophic channelized debris flow triggered by short-duration intense rainfall in Jiwozi village near Xi’an City, Shaanxi Province, China, destroying three buildings and resulting in 24 fatalities, with three people missing. This study investigates the kinematic process and underlying mechanisms of the debris flow using field investigations, terrain analysis, and numerical simulations. The rain-flood method and Rapid Mass Movement Simulation (RAMMS) software were employed to simulate the propagation process of the debris flow across 20-year, 50-year and 100-year recurrence intervals. The impact of basal friction and erosion parameters on simulation accuracy were examined based on trial-and-error approaches. The optimal parameter combinations were confirmed by comparing simulated boundaries with observed data. At two potential channel blockage sites, simultaneous increases in flow height and rapid decreases in velocity were observed. A two-factor model combining maximum flow height and velocity was utilized to construct hazard zoning. This study underscores the critical influence of local terrain on the propagation and mobility of channelized debris flow during heavy rainfall.