Flood forecasting by means of dynamical downscaling of global NWPs coupling with a hydrologic model at Nong Son-Thanh My River basins

Abstract Almost every year, Vietnam suffers floods resulting in the loss of many lives and considerable costs for damaged and lost properties. This study proposes a forecasting system that couples the dynamical downscaling technique with hydrologic models to forecast real-time flood events with a lead time ranging from one to three days. This approach is demonstrated by applying a regional numerical weather prediction and physically based hydrologic model to the Thanh My and Nong Son watersheds. System inputs are provided by two global NWPs, the global forecasting system (GFS) and the global spectral model (GSM). A WEHY-WRF was selected as the hydrologic-atmospheric component for the proposed system. WEHY-WRF was successfully implemented and validated before testing the real-time forecasting system over the Nong Son-Thanh My watersheds. Overall, the comparison between the model simulations and corresponding observations shows the rainfall and flood forecast by WEHY-WRF-GFS match quite well with observation data and perform better than WEHY-WRF-GSM. However, all forecasting results are generally encouraging considering the correlation coefficients for most events are acceptable. The forecast methodology has demonstrated it as a comprehensive reliable technology that may be universally applied for flood prediction through the coupling of dynamical downscaling technique and hydrologic models.