Post-event analysis of flash flood early warning in Wanquan River Basin, Hainan Province: A case study of typhoon “Trami” (2024)

Abstract

[Objective] To evaluate the response effectiveness of the flash flood monitoring and early warning system under extreme weather conditions, the Wanquan River Basin in Hainan Province is taken as the study area, and the rainstorm flood process triggered by the combined influence of the residual circulation of Typhoon “Trami”(2024, No. 20) and a cold air mass is used as a case study. Based on the China National Flash Flood Hydrological Model(CNFF) and the Hainan Flash Flood Monitoring and Early Warning Platform, a four-stage early warning evaluation framework covering “forecasting-monitoring-warning issuance-disaster verification” is established. [Methods]Rainfall monitoring data, hydrological model simulation result, and field survey information from 96 key villages were integrated. Using the administrative village as the evaluation unit, the hit rate of warnings at the alert level(“ prepare for evacuation”) and above was analyzed. [Results] The result showed that: the platform issued a total of 115 warnings at the level of “prepare for evacuation(alert)” and above, covering 70 administrative villages under prevention and control. Among them, 50 villages actually experienced disasters, corresponding to a warning hit rate of 71. 43%. [Conclusion] The monitoring and early warning platform has relatively strong capability in trend identification in key risk areas, but deficiencies exist in village-level response adaptability and the rationality of threshold settings. Improvement directions are proposed, including dynamic adjustment of early warning thresholds, optimization of flood process simulation, and multi-source data fusion, so as to enhance the adaptability and early warning effectiveness of the system under extreme meteorological conditions. The findings can provide a reference for the optimization of flash flood monitoring and early warning systems and the improvement of risk governance capacity in tropical monsoon regions.

Keywords

flash flood early warning / CNFF model / typhoon rainstorm / early warning system / early warning effectiveness evaluation / early warning threshold / Wanquan River Basin / influencing factors