Abstract
This paper deliberates an ensemble flood forecasting method using high-resolution ensemble rainfalls. The authors use numerical ensemble rainfalls simulated by the Japan Meteorological Agency – Nonhydrostatic Model (JMA-NHM) with a 2-km resolution as inputs to a distributed rainfall-runoff/flood inundation (DRR/FI) model. The feasibility study of the ensemble river water-stage and flood inundation depth prediction to be used for the operational forecast is carried out with DRR/FI and ensemble rainfalls. The 2-km spatial resolution of the ensemble rainfalls by JMA-NHM has a potential to be used for even small Japanese river basins such as the Sayogawa River basin (191 km2), the application site in the paper. The paper presents the ensemble simulations of the 2011flood by Typhoon No.12 in the basin. The result shows that the water stage at a given point in the Sayogawa River exceeds the evacuation call level in some ensemble members. This indicates the possibility that the ensemble flood forecasting can be used as the additional information for the evacuation call.
