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The CEMS-flood sub-seasonal and seasonal products include a basin summary of the river discharge anomaly and uncertainty information. On this layer the basin colours represents the dominant forecast anomaly and uncertainty of the river pixels of the basins.
The basin delineation was done semi-automatically, including some manual corrections and subjective decisions on where to split very large catchments and how to group small river catchments along the coastal areas. The basin borders perfectly align with the 1 arcmin (~1.5 km) LISFLOOD river network in EFAS, while follow the 3 arcmin (~5 km) river network in GloFAS down to 250 km2 pixel size. Some basins are smaller while other are larger, generally smaller over EFAS, while larger outside of the EFAS domain. In addition, the basin size was often determined by the complexity of the river network and whether splitting larger basins made practical sense, i.e. not to create too small / too many basins, in case the river network complexity would not really have allowed it.
In total, 944 basins were defined globally (Figure 1a), of which 204 are within the EFAS domain (Figure 1b). The basin size ranges from yyy1 to yyy2 km2 globally, while zzz1 to zzz2 in EFAS, with the average size of XXX1 km2 in EFAS and XXX2 km2 in GloFAS.
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Figure 1. Basins and representative points in EFAS (a) and in GloFAS (b).
GloFAS and EFAS have so-called fixed reporting points, which are used to show the forecast information regardless of the predicted conditions (CEMS-Flood diagnostic and web reporting points) and always appear as a grey rectangle. These points are not defined everywhere and therefore some of the basins in Figure 1a and 1b do not have representation, where the details of the forecast signal could be checked in a pop-out window (after clicking). Such non-represented basins appear mainly globally, lot of them in Africa and Asia, but also some in other continents. However, even in EFAS there are some non-represented basins, one or two in Italy and more in the eastern areas in Russia or the basins in Africa.
To allow at least a basic representation to all of the basins, a representative station list was defined. To allow the users to easily distinguish these from the grey rectangle fixed points, they are plotted as black dots. The basin-representative points include one single point for each basin. These representative points are the largest upstream are points, either the outlet point of the single river system in the basin, or the largest of the river catchments in the basin. This latter case happens in coastal areas, where it was not meaningful to separate out all the larger catchments, as that would have resulted in very small basins.
Figure 2 highlights a smaller area in western Europe, demonstrating how the basins and the related representative points were defined. For example, the Raine river catchment is divided into 5 basins, the lightest orange as the upstream part, then the greenish-yellow basin with the middle part of the Raine, including also the tributaries of Neckar and Main rivers. Then the lower part of Raine are all in the purple basin, except the two tributaries again of the Meuse and Moselle rivers. Each of these basins then get a representative points, one at the 'outflow' pixel, where the upstream area is the largest.
In addition, for example the pink basin north of the Raine include the Ijsselmeer and Ems rivers with many smaller coaster rivers and have one representative point on the Ijsselmeer river, which is the larger of the two main rivers in this basin.
Figure 2. Basins and representative points in EFAS over the some parts of western Europe.