Evaluation of a 4 decade pan-European database of surface precipitation for river flow modelling

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 niidnight 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).