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- Hydrological model used: LISFLOOD (LISFLOOD*)
- Meteorological forcing:
- Sub-seasonal:
- The combination of the 9km (horizontal resolution) ECMWF ensemble forecastsand the 36km ECMWF sub-seasonal forecastsfrom the same run date (see EFAS Meteorological forecasts and GloFAS meteorological forecasts for further details)
- The high-resolution medium-range and low-resolution sub-seasonal forcings are taken from the same forecast run date. The timing of the availability of the low-resolution forecasts is not an issue here, as these reforecasts are only produced retrospectively without any time constraint.
- The high- and low-resolution forcing is combined by a simple mechanical blending by using the high resolution meteorological forcing for days 1-15, while the low-resolution meteorological forcing for days 16-46, for each of the 11 ensemble members in the same order (i.e. member 1 of ECMWF ensemble forecasts and member 1 of ECMWF sub-seasonal forecasts)
- The blending can create inconsistencies locally over very complex orographical areas, due to the resolution change at day15, and also there could be some smaller inconsistencies between the ensemble because of the forcing change from 15 to 16 day, due to the mechanical blending which will mix different weather conditions from the low- and high-resolution meteorological data. However, overall as an ensemble of 11 scenarios, this will is not be expected to lead to any larger discontinuities.
- Seasonal:
- 36 km seasonal forecasts (SEAS5, LINK)
- Number of ensemble members:
- Sub-seasonal has 11 ensemble members (one unperturbed and 10 perturbed) to represent the equally likely forecast scenarios of the future.
- Seasonal has 25 ensemble members (one unperturbed and 10 perturbed) to represent the equally likely forecast scenarios of the future.
- Sub-seasonal:
- River resolution:
- 1 arcmin (~1.5 km) in EFAS
- 3 arcmin (~5 km) in GloFAS.
- Run frequency:
- Sub-seasonal reforecasts are generated always for the past 20 years. Before 12 Nov 2024, they were generated twice-weekly on Mondays and Thursdays (at 00 UTC), while from 12 Nov 2024 they are generated on given days of the months, i.e. 1, 5, 9, 13, 17, 21, 25 and 29 (excluding 29 Feb).
- Seasonal reforecasts are generated for each month of the past back to 1981, although we only use them from 2004-2023. The shorter period, in the same way as for the sub-seasonal, provides better better stationarity (see https://www.ecmwf.int/en/elibrary/81194-trends-glofas-era5-river-discharge-reanalysis), which can be very important for the reliability of the forecasts.
- Lead time:
- Sub-seasonal reforecasts have 46-day (1104 hours) lead time. This is 1-day longer than the real time forecasts, as these for the reforecasts there is no time constraint and the blending can be done with the high-resolution and low-resolution meteorological forecasts of the same run date (no need to delay by 1 day the low-resolution).
- Seasonal reforecasts have the same 7-month (or 215-day) lead time.
- Forecast steps:
- Sub-seasonal:
- EFAS: 6-hourly
- GloFAS: 24-hourly
- Seasonal: 24-hourly in both EFAS and GloFAS
- Sub-seasonal:
- Forecast hydrological initialisation
- All reforecasts are initialised from the hydrological monitoring simulation, which is forced with gridded meteorological observations in EFAS and ERA5 meteorological reanalysis data in GloFAS. There is no reason to use fillup, since these are produced for dates well in the past (as for the real time forecasts).
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