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ERA-40 stands for ECMWF Re Analysis and refers to the rerun of the European Centre of Medium Range Weather Forecast (ECMWF) Global Circulation model for the period September 1957- August 2002 utilizing all state-of-the-art information and satellite data input presently available. Here, a selection of the ERA-40 atmospheric output data at the surface is used to force the catchment hydrological model LISFLOOD to simulate historic river flows for the whole of Europe on a 5km grid resolution. Once evaluated against observed rainfall and point flow data, the output constitutes an extensive and coherent 40+ year database of pan-European calibrated river flow time series, providing a wealth of information and potential for a range of evaluation purposes. For example, statistical analyses could serve to detect flooding and/or drying frequency trends. Alternatively, the output dataset could be used to assess flood alert levels in a consistent and uniform manner at any point for any river in Europe. The set would also be extremely useful as a basis for scenario studies, investigating the impact of policy and decision making such as de/aforestation and water reservoir management on flow regimes. Further, in the context of the general scientific consensus of an expected increasing trend in extreme events, the database may serve as a resource of information for extrapolated future scenarios.

The ECMWF Re Analysis (ERA-40) refers to the rerun of the European Centre of Medium Range Weather Forecast (ECMWF) Numerical Weather Prediction (NWP) model for the period September 1957- August 2002 employing all state-of-the-art information and satellite data input presently available. A selection of the reanalysis atmospheric output data can potentially be used to run a hydrological model to simulate historic river flows for the whole of Europe. Once evaluated against observed time series of rainfall and river flow, the output would constitute an extensive and coherent 40+ year database of pan-European calibrated river flow time series, providing a wealth of information and allowing a range of evaluation possibilities. Here, in order to separate the meteorological model performance from the hydrological model performance, the ERA-40 near-surface rainfall aggregates, which come as a by-product of the ECMWF NWP system, are evaluated against interpolated fields of observed surface precipitation. The ERA-40 rainfall fields consist of forecast data with a 36 hr lead time at midday and midnight and a 6 hr lead time at 6:00 and 18:00 UTC, allowing different combinations of lead and base times to compute daily rainfall aggregates. The evaluation of these aggregated precipitation fields against observed totals is relevant to the spin-up time of the ECMWF NWP system and the forecast reliability with increasing lead time. Interpolated fields of observed daily rainfall totals are provided by the Monitoring Agriculture with Remote Sensing (MARS) database (1990-2001) based at the European Commission Joint Research Centre (JRC).