Instantaneous Response of a Tectonic–Fluvial–Lithologic Coupled System to Extreme Rainfall: Evidence From the 2023 Jinyang Torrent Event, China

Abstract. Under ongoing climate warming, extreme rainfall is becoming increasingly frequent, intensifying hazard pressure in mountainous regions where short-lived torrent events interact with long-term geomorphic evolution. Yet it remains unclear how external climatic forcing couples with the long-term antagonism between tectonic uplift and fluvial incision, and whether this coupled relationship can help identify hazard-prone geomorphic settings at the catchment scale. Here we investigate the 21 August 2023 torrent disaster in Jinyang County, Sichuan Province, China, as a representative case. Using multi-source data and quantitative analysis, we establish a regional disaster-system framework, DGR, which integrates Dynamics, Geology–meteorology cross-spatial coupling, and Risk phasing. Within this framework, we aim to capture the combined influence of endogenic tectonic forcing, exogenic hydrometeorological forcing, lithological erodibility, and human disturbance on hazard occurrence, and to provide a simplified conceptual mapping of the regional Earth system in tectonically active mountain terrain. Our results show that the disaster site was located in a runoff-incision-dominated reach characterized by disequilibrium between tectonic uplift and fluvial incision. On this basis, we propose the concept of a weak equilibrium window in the uplift–incision system, which may provide a useful geomorphic perspective for identifying potentially hazard-prone settings. Hydro-sedimentary analysis further suggests that the event was primarily flood-dominated, with sediment supplied mainly by proximal erosion rather than by sustained long-distance channel transport. Field-constrained reconstruction also indicates that engineering disturbance on the valley floor may have modified the natural transport corridor and amplified the interaction between human activity and natural hazard processes. More broadly, the results suggest that torrent disasters can serve as short-lived expressions of the long-term antagonism between internal and external geomorphic forcing. In this sense, the DGR framework provides a transferable conceptual and analytical approach for linking long-term uplift–incision evolution with short-term hazard response, and offers a practical basis for hazard identification and risk assessment in tectonically active mountain regions under climate change.