Flood inundation simulation and forecasting-response linkage mechanism in the Zuo River transboundary basin: a case study of typhoon Matmo

To evaluate the feasibility of typhoon-induced flood forecast-response linkage mechanisms in transboundary river basins, the flood event in the Zuo River basin triggered by Typhoon Matmo (No. 2521) was selected as a case study. Field surveys and measured hydrological data were utilized to calibrate the parameters of a two-dimensional hydrodynamic model and validate the inundation simulation results. By selecting forecast-response time windows across various counties, the effectiveness of the windows and the adaptability of the mechanism were analyzed. The results indicate that the accumulation of antecedent rainfall in the Zuo River basin, superimposed with rainfall during the typhoon, provided the hazard-inducing conditions for the flash flood. The regional flood inundation process exhibited high suddenness and a “negative time-lag” relative to local heavy rainfall, while the onset of heavy rainfall and the inundation time-lag both displayed marked spatial differentiation. Specifically, driven by the typhoon track, downstream and specific confluence areas experienced heavy rainfall first, whereas the upstream transboundary area exhibited a relatively shorter inundation time-lag. Directly applying a uniform forecast-response linkage mechanism in transboundary river basins entails a risk of failure. Accordingly, a differentiated forecast-response linkage strategy across three designated zones (border zone Ⅰ, border zone Ⅱ, and inland downstream zone) is proposed to serve as a reference for resolving spatio-temporal mismatches in transboundary flash flood responses.