Ensemble forecasting of typhoon rainfall and floods over a mountainous watershed in Taiwan

•Ensemble forecast of typhoon tracks has a comparable skill to operational centers.•Ensemble forecast has better performance for rainfall than a deterministic forecast.•Ensemble prediction provides useful probabilistic information.•Runoff forecast over mountainous watershed is sensitive to rainfall forecast.

SummaryIn this study, an ensemble meteorological modeling system is one-way coupled with a hydrological model to predict typhoon rainfall and flood responses in a mountainous watershed in Taiwan. This ensemble meteorological model framework includes perturbations of the initial conditions, data analysis methods, and physical parameterizations. The predicted rainfall from the ensemble meteorological modeling system is then used to drive a physically distributed hydrological model for flood responses in the Lanyang basin during the landfall of Typhoon Nanmadol (2011). The ensemble forecast provides track forecasts that are comparable to the operational center track forecasts and provides a more accurate rainfall forecast than a single deterministic prediction. The runoff forecast, which is driven by the ensemble rainfall prediction, can provide uncertainties for the runoff forecasts during typhoon landfall. Thus, the ensemble prediction system provides useful probability information for rainfall and runoff forecasting.