The CEMS-flood sub-seasonal and seasonal products are essentially the same across the two systems and similarly the same across EFAS and GloFAS. Below we introduce the available products.
River network summary map
The river network summary map layer shows the combined forecast anomaly and uncertainty signal in a simplified way for each forecast lead time (Figure 1). The lead time is weekly (always Monday to Sunday, with the weekly average river discharge) in the sub-seasonal and monthly (always calendar month, with the monthly average river discharge).
The forecasts can be advanced (or even animated if needed) with the lead time controller (see Figure 1a bottom left corner) and the users can check the individual signal for each lead time, which currently is 5 or 6 weeks for the sub-seasonal (depending on which day of the week the run date is) and always 7 months for the seasonal.
The forecast signal is shown by colouring of all river pixels above a certain minimum catchment area (currently 50 km2 in EFAS and 250 km2 in GloFAS). Each of these river pixels are coloured by the dominant anomaly category and by the uncertainty category.
There are 7 anomaly categories and three uncertainty categories defined based on the extremity level of the ensemble forecast members in the 99-value percentile climatological distribution. The details of the computation methodology is described here: Placeholder CEMS-flood sub-seasonal and seasonal forecast anomaly and uncertainty computation methodology.
On the river network summary map, however, only 5 anomaly categories are displayed, after combining the middle three into one larger 'Near normal' category, which allow the users to focus visually on the larger anomalies. Each of these categories are divided into three sub-categories by the uncertainty, as low, middle and high uncertainty, in total making it into 15 forecast signal categories. The inset figure in both Figure 1a and 1b shows the 15 categories and the corresponding colours on the maps.
Figure 1a highlights some river sections with the explanation of the assigned colours and the corresponding anomaly and uncertainty levels. Each of the 5 anomaly categories have a distinct colour, where the 3 uncertainty categories is indicated by lighter colours as the uncertainty increases.
The river network summary map also contains the reporting points, which are labelled as example in Figure 1b. These are river locations, where detailed information is provided about the evolution of the forecast signal over the forecast horizon. There reporting points are either fixed points, which are also used in the medium-range flood products and the basin-representative points, which are selected locations, on a one point per basin basis. Further details about the basins and the representative points are available here: Placeholder CEMS-flood sub-seasonal and seasonal basins and representative stations.
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Figure 1. Example snapshots of the sub-seasonal and seasonal river network summary maps with the reporting points, animation and river pixel colours explained.
Reporting point pop-up window
At the predefined reporting point locations (either fixed or basin-representative) further detailed information is provided about the evolution of the forecast signal.
Point information section
The first table in the popup window ('Point information' provides metadata information of the station (Figure 2). These are the station ID and also an internal ID (Point ID), the station name (if available), country, basin and river names, and also coordinates (lat/lon) and upstream area in two flavours, the provided ones and the LISFLOOD river network equivalent. The provided coordinates and upstream area are from the users as those represent the real river gauge location. These are available only for the fixed points (sometimes provided upstream area is missing). For the basin-representative points, however, only the LISFLOOD coordinates and upstream area are available, as these points were defined solely on the simulated LISFLOOD river network. The fixed reporting points have a Point ID in the metadata table starting with 'SI', while the basin-representative points starting with 'SR'.
Hydrograph section
Next in the popup window is the hydrograph, which graphically summarises the climatological, antecedent and forecast conditions.
The left half of the plot, left of the horizontal dotted line, which indicates the forecast start date, shows the past (see Figure 2a). The black dots (connected by black line) indicate the so-called water balance, the proxi observations, which are produced as a LISFLOOD simulation forced with either gridded meteorological observations in EFAS, or ERA5 meteorological reanalysis fields in GloFAS. These black dots show the simulated reality of the river discharge conditions, as close as the simulations can go at the actual periods (average river discharge over months in seasonal and weeks in sub-seasonal).
These black dots are added to the hydrographs retrospectively, after each week (in sub-seasonal) or month (in seasonal) passes and the weekly or monthly mean proxi-observed river discharge values become available. The users are encouraged to go back and check previous forecasts to see how well the earlier forecasts predicted the anomalies.
The right half of the plot covers the forecast horizon, in the displayed example in Figure 2 and 3 this means 7 lead times of 7 calendar month from August to February the next year (see Figure 2a). The forecast distribution is indicated by box-and-whiskers, displaying the minimum and maximum values in the ensemble forecasts of all the 51 members and the lower and upper quartiles (which are the 25th and 75th percentiles as well) and the median (which is the 50th percentiles).
The coloured background is the model climatology. This climatology is generated using reforecasts over a 20-year period. In the past half
Placeholder CEMS-flood seasonal forecast generation methodology
Probability table section
Figure 2. Example snapshot of the reporting point pop-up window product (for a seasonal forecast).
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Figure 3. Different interpretation helps (a-b-c) for the sub-seasonal and seasonal hydrographs.