PROBABILISTIC RUNOFF FORECASTING USING A COUPLED ATMOSPHERIC-HYDROLOGIC ENSEMBLE PREDICTION SYSTEM

A high-resolution atmospheric ensemble forecasting system, based on 51 runs of the Local Model (LM), has been used to make probabilistic runoff forecasts for a 5 day forecasting period in the alpine tributaries of the Rhine basin. The investigated cases are the spring 1999 flood, when a combination of snowmelt and heavy precipitation caused severe floods in Central Europe and the November 2002 flash flood in the Alpine Rhine area. This study focuses on the feasibility of ensemble prediction system (EPS) for runoff forecasting. Runoff predictions from the deterministic forecast are compared with those obtained from probabilistic atmospheric forecasts. For both cases, the deterministic simulations yield large forecast failures, while the hydrometeorologic EPS provides appropriate forecast guidance with proper uncertainty intervals. The use of clustering techniques showed that the clustering methodology does not reduce ensemble spread