Assessment of High-resolution Ensemble NWP Rainfall for Flood Forecast of Relative Large River Basin in Japan

Abstract

In early September, 2011, Typhoon Talas caused local heavy rainfalls over the Kinki, Chugoku, Shikoku and Tokai regions in Japan. In these types of extreme events, it is essential to be able to provide as much advance warning as possible. This advance warning requires both quantitative precipitation forecasting (QPF) and quantitative flood forecasting (QFF). The operational meso-scale model of the JMA generally predicted the typhoon track well in the early period. However, the rainfall intensity was weaker than expected, and the movement was also faster when the lead time was longer. The latest ensemble NWP forecast with 30hr forecast time and 2km horizontal resolution has been generated by the Meteorological Research Institute (MRI) of the JMA. In this study, we assessed the latest ensemble NWP outputs with 30hr forecast time and 2km horizontal resolution from MRI whether they can produce suitable rainfall predictions or not during the Typhoon Talas event, and we also assessed the performance of ensemble flood forecasting for hydrological applications based on the latest ensemble NWP forecast with 30hr forecast time and 2km horizontal resolution. As a result, ensemble rainfall prediction produced more suitable results compared with a deterministic control run in terms of QPF. Ensemble flood forecasting driven by ensemble rainfall forecasts could also produce comparable results in comparisons of observed data, although the maximum peak discharge value was underestimated.