GloFAS Seasonal outlook

How are GloFAS Seasonal forecasts generated?

From GloFAS 3.1, GloFAS Seasonal modelling chain is based on the Open Source LISFLOOD hydrological model, forced by an ensemble of meteorological forcings. A 5-day monitoring analysis of the latest observations based on the latest ECMWF reanalysis when available is used to initialize the forecasts, followed by seasonal ensemble forecasts for 16 weeks from the latest ECMWF Seasonal Forecast System, SEAS5. The resulting 16 weeks simulated daily hydrological forecasts are then averaged by calendar weeks (GloFAS Seasonal) and compared with GloFAS Seasonal reforecasts to create an ensemble of weekly river flow anomalies, converted into a probability of unusually high or low flows.

This page provides a detailed description of the meteorological forcings used in GloFAS.

Which products does GloFAS Seasonal offer?

GloFAS Seasonal offers a range of forecast products and associated information, accessible via different layer tabs of the GloFAS map viewer:

• Under the hydrological tab, maps of where a high/low flow signal is expected over the GloFAS river network or on specific catchments over the next 16 weeks
• Under the evaluation tab, maps of hydrological model performance and seasonal forecast skill

GloFAS Seasonal products are updated monthly and published on the 10th of each the month. Detailed information on GloFAS Seasonal products can be found in the GloFAS seasonal forecasts products wiki pages.

The GloFAS User Guide provides hands-on information on how to explore the tabs and layers of the Map Viewer.

GloFAS Seasonal reference discharge runs

GloFAS Seasonal reference discharge runs are a collection of discharge simulations as close as possible to GloFAS Seasonal operational system. GloFAS Seasonal reforecasts are forecast simulations performed for a set of past dates using the latest ECMWF Seasonal forecasting system, based on a configuration as close as possible to GloFAS Seasonal operational setting, initialised using GloFAS reference long run. They are used to compute GloFAS Seasonal reference discharge runs and to analyse GloFAS Seasonal forecast performance systematically over a long period. GloFAS Seasonal discharge thresholds are a set of maps of weekly-averaged discharge magnitude corresponding to the 20th and 80th percentile values (respectively called low and high flow thresholds). There is a set of maps for each week of the year and each lead time from 1 week to 16 weeks. The percentiles are derived from GloFAS Seasonal reforecasts for the corresponding week of the year and lead-time sample. GloFAS Seasonal discharge thresholds are used to generate river flow anomaly forecast maps.
For more details on the latest GloFAS configuration, please refer to the GloFAS wiki pages.

GloFAS Seasonal data

GloFAS Seasonal data is a gridded dataset at 0.05° horizontal resolution from GloFAS 4.0 (July 2023), at 0.1° horizontal resolution for all the previous versions. It includes:

• Real time forecasts of weekly-averaged discharge with 51-member ensemble from the 1st calendar week of each month to the end of the 4 months (for 16 calendar weeks). Real-time forecasts are publicly available few days after the 1st of each month.
• Reforecasts of weekly-averaged discharge out to 4 months (also for 16 calendar weeks):
  • For the period of 1981-2016 with 25 ensemble members
  • From 2017 with 51-ensemble members

The CEMS-Flood Data User Guide provides detailed instructions on how to download and work with GloFAS data.