GloFAS v4.0 hydrological model
GloFAS v4 reanalysis, forecasts, and reforecasts are generated using the open-source hydrological model LISFLOOD OS. LISFLOOD OS is a distributed, physically based hydrological model which has been developed by the Joint Research Centre (JRC) of the European Commission since 1997 (De Roo et al., 2000). LISFLOOD OS is particularly suited for the modelling of rainfall-runoff processes in large catchments: starting from GloFAS v3.1 (operational release: 2021-05-26), LISFLOOD OS is the sole model at the core of GloFAS.
LISFLOOD OS is able to represent all the main hydrological processes: partition of precipitation into rain and snow, snow melting, canopy interception of rain, water infiltration into the soil, groundwater storage, surface runoff, lakes, dams, irrigation, and other human water uses, flow in the rivers and in the floodplains. The numerical simulation is driven by meteorological forcing data (precipitation, temperature, and evapotranspiration). A set of raster maps showing the terrain morphology, soil properties, land cover and land use features, water demand, enables the modelling of runoff processes in different climates and socio-economic contexts. LISFLOOD OS solves the water balance at each time step and for each grid cell.
Specifically, GloFAS v4 makes use of LISFLOOD OS v4.1.3. Compared to the LISFLOOD OS version used to produce GloFAS v3, LISFLOOD OS v4.1.3 features updates in the hydrological routines, such as pixel-by-pixel computation of water infiltration into the soil, and improvements in the modelling of water abstraction for anthropogenic use. Moreover, LISFLOOD v4.1.3 benefits of significant improvements in the management of large input datasets and in the computational performances.
Consistently with all the previous GloFAS versions, the computations for GloFAS v4 are completed with daily time steps for all the hydrological processes, while sub-daily (4 hours) time steps are used for the modelling of river routing. All the output variables are available with daily resolution.
GloFAS v4.0 implementation set-up
Static maps
Accurate representation of the rainfall-runoff processes in different climatic and socio-economic contexts requires a set of maps showing the morphological, pedological, vegetation, land use, land cover characteristics of the catchments. About 80 implementation maps are required as input to LISFLOOD OS. This set of implementation maps is traditionally called “static maps”.
The spatial resolution of the GloFAS v4 implementation maps is 0.05 degrees, which is four times higher than the previous 0.1 degrees GloFAS v3. The much higher resolution of GloFAS v4 allows a more detailed representation of the river network and of the spatial variability of catchments’ characteristics. The benefits of using a higher spatial resolution can be appreciated in Figure 1: smaller tributaries can be more adequately represented when using 0.05 degrees resolution.
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.