GloFAS seasonal outlook

This page summarises the important features of the GloFAS seasonal outlook products. Further information on the details of the different steps generating these products is available at CEMS-flood sub-seasonal and seasonal forecast product generation methodology.

'Seasonal Outlook' and 'Seasonal Outlook - Basins' layers

The GloFAS seasonal outlook layers show maps of the 'expected to happen' forecast anomaly and related uncertainty for the next 7 months for all river pixels over 1000 km² (river network layer called 'SeasonalOutlook' on the mapviewer) and for 942 major river basins over the GloFAS domain (basin layer called 'SeasonalOutlook - Basins' on the mapviewer), using colour-coded categories (see Figure 1). The products are updated once a month and published around the 8^th of the month, showing:

• forecast anomaly expressed in one of 5+2 categories from extreme low to extreme high, which are derived from specific model climatology percentiles
• forecast uncertainty is categorised into low, medium and high levels, based on the spread of the ensemble member extremity levels

The forecast anomaly and uncertainty are based on the extremity levels of the monthly averaged river discharge of the ensemble members in the context of the model climatology. The model climatology is range-dependent (change with the lead time) and generated from 20 years of reforecast hydrological simulations (2004-2023).

The forecast evolution of the anomaly is also given in popup window products for fixed reporting points (grey squares along the river network) and basin-representative points (black circles, one point for each of the 204 predefined basins).

Figure 1: GloFAS seasonal outlook on the GloFAS-IS map viewer. A lead-time selection panel on the mapviewer allows the users to select the forecast month.

Reporting point pop-up window product

From the river network map, the reporting point pop-up products can be accessed by clicking on the point markers on the river network layer (grey squares showing the GloFAS fixed reporting points - see more in CEMS-Flood reporting points and dynamic point generation algorithm, and the black circles showing the basin-representative points - see more in CEMS-flood sub-seasonal and seasonal basins and representative stations). The pop-up products contain metadata information about the stations, a hydrograph with the evolution of the climatological, antecedent and forecast conditions (see Figure 2), and the probability values for the extended 7-value anomaly categories (the 5 main categories shown on the maps and hydrographs, extended by two additional categories within the 'Near normal' category) and the evolution of these probabilities from previous forecast runs.

Figure 2: Discharge hydrograph showing weekly-averaged antecedent and climate conditions and forecast evolution out to 7 months.

Figure 3: Forecast probability evolution table with (a) probabilities values (as numbers) for all anomaly categories with the extended 7-category version ('Extreme low' (EL), 'Low' (L), 'Bit low' (BL), 'Normal' (N), 'Bit high' (BH), 'High' (H) and 'Extreme high' (EH), as left to right); (b) ‘expected to happen’ anomaly category as the one coloured cell at each monthly forecast lead time, the colour dependent on the anomaly and on the related forecast uncertainty category (how uncertain the forecast is; either low, medium or high). Each main column (7-column groups) represent a monthly forecast lead time and the 7 rows show the 7 most recent forecast start dates (the most recent being on top), which are always the 1st of the month (indicated only by month and year).

Different legends to help interpreting the forecast signal