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Figure 1 - River network at 0.1 degrees resolution (left) and 0.05 degrees resolution (right): drainage upstream area with increasing values from 50 km2 represented with colours from blue to yellow. The HydroRIVERS dataset is used as reference.
Moreover, the latest research findings, remote sensing and in-situ datasets were used to prepare the 0.05 degrees resolution implementation maps. Examples include the latest land cover information and leaf area index layers from the Copernicus Global Land Service, global hydrology datasets based on MERIT Hydro, and global soil data from ISRIC.
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The higher resolution and quality of the 0.05 degrees implementation set-up is expected to lead to a more realistic representation of the hydrological processes, and therefore to more accurate modelling of river discharge and hydrological state variables (e.g. soil moisture).
The GloFAS v4 implementation maps dataset is presented in Choulga et al. 2023[1] and the maps are available for download from the Joint Research Centre Data Catalogue [readme]. The complete list of source data and a detailed description of the methodology used to produce each map is available here.
GloFAS v4.0 meteorological input data
The meteorological variables used by GloFAS v4 (and GloFAS v3) are total precipitation, 2-metre temperature, 2-metre dew temperature, 10-metre U wind component, 10-metre V wind component, surface solar radiation downwards, surface thermal radiation.
These variables are provided as input to GloFAS from different meteorological datasets, depending on the purpose of the model simulation: hydrological reanalysis, medium range forecast, seasonal forecast. The list of meteorological datasets used for each purpose is available here.
The meteorological variables are upsampled from their native resolution to 0.05 degrees resolution using bilinear interpolation: the interpolation algorithm is implemented in the open-source pre-processor pyg2p. It is here noted that nearest neighbor interpolation was used for 0.1 degrees GloFAS set up (v3 and preceding versions).
2-metre temperature, 2-metre dew temperature, 10-metre U wind component, 10-metre V wind component, surface solar radiation downwards, surface thermal radiation are used to compute reference values of evapotranspiration according to the Penmann-Monteith equation, which is implemented in the open source pre-processor LISVAP .
LISFLOOD OS then takes as input total precipitation, 2-metre temperature, and reference evapotranspiration. Similarly to all the previous GloFAS versions, the computations for GloFAS v4 are completed with daily time steps for all the hydrological processes, and sub-daily (4 hours) time steps for the river routing. All the output variables are available with daily time steps.
[1] Choulga, Moschini, Mazzetti, Grimaldi, Disperati, Beck, Salamon, and Prudhomme. “ Technical note: Surface fields for global environmental modelling”. Submitted for publication to HESS, MS type: Technical note