The meteorological forcing data are all the information necessary to produce hydrological simulations.

• Historical hydro-meteorological time series:  they are used to calibrate the hydrological model, and to define the flood thresholds used to derive some GloFAS products. GloFAS uses the ECMWF-C3S ERA5 reanalysis a proxy meteorological observation and a range of hydrological observational records, managed jointly by the JRC and the Computational centre (COMP)
• Real-time hydro-meteorological observations: they are necessary to define the starting points of the hydrological forecasts, also called initial conditions. GloFAS uses the unconsolidated ECMWF-C3S ERA5-T reanalysis a proxy meteorological observation until it is available, and the first day of the control member of the ECMWF-ENS forecast for the remaining days until the forecast initial time (usually only 1 or 2 days) 
• Meteorological forecasts: they are used to provide the meteorological input to the hydrological models generating the future predictions. These predictions are ensemble forecasts in GloFAS, i.e. multiple realisations -also called ensemble members- produced by a single numerical weather prediction system.