[A-AS05] Weather, Climate, and Environmental Science Studies using High-Performance Computing

[AAS05-05] Flood forecasting using 1000-member ensemble prediction for a severe flood event

*Tsutao OIZUMI^1,2, Takuya Kawabata², Le Duc^3,2, Kenichiro Kobayashi^4,2, Kazuo Saito^5,2,1, Takuma Ohta⁶ (1.Japan Meteorological Business Support Center, 2.Meteorological Research Institute, 3.The University of Tokyo , 4.Kobe University, 5.The Atmosphere and Ocean Research Institute, The University of Tokyo , 6.Japan Meteorological Agency)

Keywords:Flood forecasting, ensemble weather forecast, Flood disaster

This study is the first study realizing “Impact-based forecasts and warnings” for severe flooding. “Impact-based forecasts and warnings” is a new concept proposed by WMO that predicts not only extreme weather conditions but also damage levels of disasters. We developed an ensemble flood forecast system that predicts the probability of flooding nationwide in three damage levels. The feature of this system is that it uses an operational flood forecast model "Rainfall Index Model" in Japan in combination with a large ensemble weather forecast. This study investigated the impacts of a large ensemble size (1000) on the probability of occurrence of flooding for the different sizes of river basins. The system predicted the maximum probability of exceeding the historical magnitude flood of 60% 11 hours before the flood event.