Uncertainty Evaluation in a Flood Forecasting Model Using JMA Numerical Weather Prediction

Abstract

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.

Flood Forecasting and Early Warning for River Basins in Central Vietnam

“…It is also based on the original tank, attributes with some physically based features 4) and nearly calibration-free parameters, because the model parameters have been internally calibrated using geo-topographical and land-surface information. In addition, the super tank model is semi-distributed, it is assumed to outperform lumped hydrologic models in terms of spatial variation consideration.…”

“…Recent studies demonstrated that the major source of model uncertainties is mostly induced by the NWP due to its intrinsic errors 4) . The forecast uncertainties are likely to be larger along with the forecast lead-time.…”

“…Because it just depends on the lead-time of precipitation prediction that varies from few hours to a couple of days for a short-range forecast and up to 10 days or more for a medium-range forecast. These studies used either very short-range deterministic NWP models (usually high resolution models) such as Mesoscale Model 4) , limited area models 5) , or medium-range ensemble prediction system 1), 2) . The high resolution models driven flood prediction have demonstrated very high forecast skills; however, these high resolution models are restricted either at relatively short-term forecast or regionally bounded.…”

Distributed flood model for urbanization assessment in a limited-gauged river basin

“…The rest of the precipitation will fall to the surface and become surface runoff, but some will be infiltrated through the soil layer and recharge the sub surface water. Surface run off is simulated by a two-dimensional shallow water equation while a NCF tank model [11] is applied at each grid of the domain. where u and v are the velocities in the corresponding axes, h is the water depth, q is the outsource term, and f S is the friction slope calculated with manning roughness ( n ) using eqns.…”

Uncertainty assessment for short-term flood forecasts in Central Vietnam

“…However, flood forecast models are subject to uncertainty in general, especially those are based on rainfall prediction obtained directly from the NWP model output. The errors in rainfall, even predicted by high resolution models, have been observed as the most significant contribution to the total model uncertainty (Kardhana and Mano [4], Xuan et al [5]). …”