What is GloFAS Seasonal?
How are GloFAS Seasonal forecasts generated?
GloFAS Seasonal modelling chain is based on a coupled land-surface and 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 initialise the forecasts, followed by seasonal ensemble forecasts for 16 weeks from the latest ECMWF Seasonal Forecast System. The resulting 16 weeks simulated daily hydrological forecasts are then averaged by calendar weeks (GloFAS Seasonal) and compared with GloFAS Seasonal forecast reruns to create an ensemble of weekly river flow anomalies, converted into a probability of unusually high of low flows (for further details see Emerton et al., 2018).
Schematic of GloFAS Seasonal modelling chain
Which products does GloFAS Seasonal offer?
- River basin probabilities: A summary map at regional scale, where GloFAS Seasonal outlooks are averaged over 305 major river basins of the world. The map shows the maximum probability of unusually high or low weekly mean river flow expected during the four months forecast horizon.
- River network probabilities: A summary map at river scale, where GloFAS Seasonal outlooks are shown for the GloFAS river network of all catchments larger than 1500km2. The map shows the maximum probability of unusually high or low weekly mean river flow expected during the four months forecast horizon.
- Forecast details: Additional information for selected river points, including time evolution of the streamflow forecast for the next 16 weeks, and a summary of forecast probabilities of four previous GloFAS Seasonal forecasts showing consistency in the forecast signal.
GloFAS Seasonal reference discharge runs
GloFAS Seasonal reference discharge runs are a collection of discharge simulations as close as possible to GloFAS Seasonal operational systemGloFAS Seasonal hydrological reanalysis is set of proxy-observation, deterministic time series of hydrological variables, including river discharge, produced from atmospheric forcing as close as possible to observations, using the same modelling chain as GloFAS Seasonal to avoid the introduction of systematic biases. It is used to as initial conditions of GloFAS Seasonal forecast reruns and to conduct GloFAS Seasonal forecast skill assessments. In practice, and when possible, GloFAS Seasonal hydrological reanalysis is identical to GloFAS 30-day reanalysis.
GloFAS Seasonal forecast reruns 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 30-day 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 map for each week of the year and each lead time from 1 week to 16 weeks. The percentiles are derived from GloFAS Seasonal forecast reruns for the corresponding week of the year and lead-time sample. GloFAS Seasonal discharge thresholds are used to generate river flow anomaly forecast maps.
GloFAS Seasonal data
- a 51-member ensemble real-time weekly-averaged discharge forecasts from the 1st calendar week of each month to the end of the fourth months (16 weeks). Real-time forecasts are publicly available on the 10th of each month.
- 25-member ensemble weekly-averaged discharge forecast reruns, out to 4-month.
- A set of weekly-averaged discharge thresholds corresponding to the 20th and 80th percentiles, defined weekly and per lead time.
Note that the complete dataset is only available for the GloFAS Seasonal v2.0 cycle.