The 3rd HEPEX Workshop - Book of Abstracts


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The scope of EFAS is to raise preparedness previous to a possibly upcoming flood event in order to leave more time for the organization of countering measures and mitigation. Furthermore, EFAS gives a, hitherto not available, unified overview of flood forecasts over the whole of Europe that uses the same warning nomenclature for all river basins thus facilitating a trans-national overview. EAFS is making use of deterministic weather forecasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) and of the German national weather service (DWD). The probabilistic forecasts (51 members) are based on the Ensemble Prediction System (EPS) of ECMWF.

The objective of this work is to assess the skill of this specific operational hydrological forecasting system, which to this extend (to the knowledge of the author) has not been reported in literature before. For this purpose 2 years of pre-operational EFAS medium-range deterministic and probabilistic flood forecasts with up to 10 days in advance were analysed statistically for the whole of Europe.

Because of (distributed) nature of EFAS this data intensive skill assessment cannot make use of the traditional hydrological approach as it cannot make use of observed discharges, in fact it is using a proxy (hydrologic simulation with observed meteo data).

Most suitable skill scores and visualizations are reviewed and pros and cons are analysed. This skill assessment is looking at the past performance but is also designed to improve the future performance of such a system by making it possible to incorporate the past experience into the current forecast. By making the past performance easily accessible at each pixel the forecaster can better evaluate the probability of a current forecast. This is especially useful as the study showed that the meteorological assumed equi-probability of forecast members does (in the case of EFAS) not linearly translate into the hydrological probabilistic forecasts and that there are biases.

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