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The basin summary map is the equivalent of the river network summary map on a larger basin scale. The basins are predefined, as described in in Placeholder CEMS-flood sub-seasonal and seasonal basins and representative stations, with 204 basins in the EFAS domain and 944 basins globally in GloFAS.

Figure 4 shows an example snapshot in the same area as Figure 1a above. One can compare, how the variable signal on the river network averages into the basin signal. The averaging is done from the river pixel information. A Rank-mean and a Rank-std value will be calculated for each basin and with those the exact same method is used (as for the river pixels on the river network summary map) to define the dominant anomaly category and the uncertainty category and thus the colour of the basin (see the inset figure with the colour legend in Figure 4). The colours used are the same as for the river network summary map, except there is a slight shift in transparency, in order to allow visibility for all river pixels, even for those with the same colour as the basin colour.

The basin Rank-mean and Rank-std values are determined using all the large enough river pixels in the basin. Currently, only pixels above 50km² are used in EFAS and pixels above 250 km² are used in GloFAS. The basin Rank-mean/Rank-std values will be calculated as an arithmetic average of the Rank-mean and Rank-std values of the individual river pixels, weighted by the square of the upstream area, as described below:

in the averaging.average Rank-mean is calculated as the arithmetic mean of the Rank-mean values of the river pixels in the basin, while the basin-average Rank-std is calculated again as the arithmetic mean of the Rank-std values at the pixels. 

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Figure 4. Example snapshot of the sub-seasonal and seasonal river network summary maps with the animation and river pixel colours explained.

At the predefined reporting point locations (either fixed or basin-representative) further detailed information is provided about the evolution of the forecast signal.

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