Uncertainty Evaluation in a Flood Forecasting Model Using JMA Numerical Weather Prediction
Hadi Kardhana* and Akira Mano**
*Water Resources Engineering Research Group, Institut Teknologi Bandung, Jl. Ganesha 10 Bandung, Jawa Barat, Indonesia
**Graduate School of Engineering, Tohoku University, 6-6-11-1110 Aramaki, Aza-Aoba, Aoba-ku, Sendai 980-8579, Japan
Numerical weather prediction (NWP) is useful in flood prediction using a rainfall-runoff model. Uncertainty occurring in the forecast, however, adversely affects flood prediction accuracy, in addition to uncertainty inherent in the rainfall-runoff model. Clarifying this uncertainty and its magnitude is expected to lead to wider forecast applications. Taking the case of Japan’s Shichikashuku Dam, 6 flood events between 2002 and 2007 were analyzed. NWP was based on short-range forecasts by the Japan Meteorological Agency (JMA). The rainfall-runoff model is based on a distributed tank model. This research calculates uncertainty by identifying and quantifying the relative error of forecasts by a) NWP and b) the runoff model. Results showed that NAP is the main cause of flood forecast uncertainty. They also showed the correlation between forecast lead time and uncertainty. Uncertainty rises with longer lead time, corresponding to the magnitude of observed discharge and precipitation.
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