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GloFAS Seasonal (Global Flood Awareness System — seasonal forecast)

What this model is

GloFAS Seasonal is the long-range configuration of the Copernicus Emergency Management Service global river discharge forecast. It runs the same LISFLOOD hydrological model on the same 0.05° global grid as GloFAS Forecast, but is forced with ECMWF's SEAS5 seasonal ensemble instead of medium-range meteorology, initialised once a month and extending to 215 days.

It forecasts discharge, not water level.

This entry is filed under hydrological_models/ rather than climate_models/, following the repository's convention that seasonal forecasts of a phenomenon use the phenomenon's template and sit beside their medium-range siblings. It uses hydrological-model.template.md with the optional Long-range configuration section retained, and points upstream to SEAS5 rather than duplicating that system's coupled configuration. Cross-linked in both directions with GloFAS Forecast.

Who runs it

  • Organization: Copernicus Emergency Management Service (CEMS) — European Commission Joint Research Centre (JRC), implemented by ECMWF
  • Country / region: International (European Union programme)

What area it covers

  • Coverage: Global except Antarctica
  • Domain details: 90°N–60°S, 180°W–180°E, regular latitude–longitude grid on EPSG:4326 — identical to the medium-range product
  • Grid dimensions (computed, not file-verified): 7200 × 3000 at 0.05°

Basic details

  • Model type: Ensemble hydrological model (seasonal range)
  • Core hydrological model: LISFLOOD (open source; JRC)
  • Forecast length: 5160 h (215 days), 215 lead-time steps at 24-hour intervals — verified against the EWDS request constraints
  • Update frequency / cycles: monthly, initialised on the 1st at 00 UTC
  • Publication: made available on the 10th of each month
  • Temporal output resolution: 24 h
  • Operational system version: GloFAS v4.5 (16 April 2026). Legacy versions version_2_2 and version_3_1 remain retrievable.

Grid and river network

  • Land surface grid: 0.05° (~5 km at the equator). Raised from 0.1° at v4.0.
  • Routing geometry: Gridded routing on the same 0.05° grid; no reach-indexed channel product
  • Calibration: shared with the operational GloFAS chain — 1995 in-situ gauging stations with parameter regionalisation for ungauged catchments (v4.0)
  • Reservoir and lake representation: TBD

Meteorological forcing

  • Driving atmospheric model: SEAS5 — ECMWF's seasonal forecasting system, 51 members at ~36 km, initialised monthly from the 1st with 7-month lead time (extended to 13 months once a season)
  • Forcing quantity: downscaled runoff forecasts from SEAS5, rather than downscaled precipitation and temperature. This is a meaningful difference from the medium-range chain and from EFAS Seasonal, and it means part of the land surface response is inherited from the SEAS5 land model rather than computed by LISFLOOD. (TBD — the downscaling method is not described on the public pages.)
  • Bias correction: TBD

Initialization and antecedent state

  • Initial state source: the operational GloFAS chain's continuous simulation at the start of the month (TBD — not documented in detail for the seasonal configuration specifically)
  • Assimilates discharge observations: TBD
  • No-DA variant published? No

Ensemble configuration

  • Ensemble size: 51
  • Source of perturbations: inherited entirely from SEAS5. The hydrological model is not perturbed.
  • Member packaging: unlike the medium-range dataset, the request form exposes no product_type selector — control and perturbed members are not separable at request time
  • Derived products distributed: none as raw data. The monthly discharge anomaly categories shown on GloFAS-IS are viewer products, not downloadable grids — out of scope.

Long-range configuration

  • Driving long-range system: SEAS5
  • Initialization cadence: 1st of each month
  • Hindcast (reforecast) period: 1981–2016 with 25 members, 2017 onward with 51 members, following SEAS5's own reforecast configuration
  • Reference climatology period: 1979-01-01 to 2022-12-31 for thresholds and anomalies (GloFAS v4 reference climatology)
  • Hindcasts distributed alongside forecasts? No — separate dataset, cems-glofas-seasonal-reforecast on EWDS. The seasonal reforecasts are used to derive a forecast-range-dependent climatology, so anomaly products are not computed against a single fixed baseline.
  • Sources of predictability: TBD — not documented on the public pages. Note the general point that seasonal hydrological skill often leans more on initial catchment storage than on atmospheric predictability, which the range-dependent climatology design implicitly acknowledges.

What it provides

  • River discharge in the last 24 hours (m³ s⁻¹, surface level)
  • Soil wetness index (root zone) (sub-surface)
  • Snow depth water equivalent (surface)
  • Runoff water equivalent (surface plus subsurface) (sub-surface)

Time-invariant ancillary files, required for interpretation and version-matched to the forecast:

  • Upstream area (m² per river pixel)
  • Elevation

Data availability

  • Is the data free? Yes, with free self-registration on the CEMS Early Warning Data Store
  • License: CEMS-FLOODS datasets licence — free reproduction, distribution, communication to the public, and adaptation. Attribution required: "Generated using Copernicus Emergency Management Service information [Year]", or "Contains modified Copernicus Emergency Management Service information [Year]" for adapted data. No share-alike or non-commercial restriction. The EWDS catalogue API reports license: other; the full text is linked below.
  • Is the data downloadable? Yes
  • Output geometry: Gridded fields only
  • Real-time availability: Current, no embargo. Catalogue temporal extent ran to 2026-08-01 when checked on 2026-08-11, consistent with monthly initialisation and the documented 10th-of-month publication. cads:update_frequency is Monthly.
  • Data formats: GRIB2, and NetCDF-4 offered in the request form
    • Note — format documentation conflict. The CEMS Model Output page lists File format as GRIB2 only for this dataset, while the live EWDS request form offers both grib2 and netcdf. The form is the operative source; the documentation is stale.
  • Official download location: https://ewds.climate.copernicus.eu/datasets/cems-glofas-seasonal
  • DOI: https://doi.org/10.24381/cds.00b6c4fb
  • Archive extent: 2020-12-01 to present
  • Access route notes: API request against the EWDS processes endpoint with an account key, or the web form. No anonymous directory tree.

Verification status. Verified live against the EWDS catalogue, request form, constraints and licence endpoints, plus ECMWF CEMS documentation. No GRIB or NetCDF file was decoded — EWDS retrieval requires an authenticated account key — so grid dimensions, GRIB parameter encoding, packing and bitmap coverage are documentation-derived and unconfirmed.

Notes

  • Documentation error — forecast length. The EWDS dataset description states the forecasts "cover 123 days". They do not. The live request constraints expose 215 lead-time steps to 5160 h, and the CEMS Model Output page resolves the contradiction: the forecasts covered 123 days until May 2021 and 215 days from June 2021 onward. The dataset description on the data store has not been updated in five years. Anyone sizing a request from the description will under-fetch by 92 days.

  • Documentation error — resolution. The CEMS Model Output page's prose for this product states LISFLOOD is forced "at a 0.1° (~11 km at the equator) resolution", while its own technical table two lines below states 0.05°. The prose is stale text predating v4.0 (July 2023). The correct figure is 0.05°.

  • The EWDS catalogue bounding box is wrong. The STAC record reports bbox: [0.0, -60.0, 360.0, 90.0], which is a 0–360 longitude convention against a documented −180/+180 grid. The medium-range record carries a different and equally implausible box. Do not use catalogue geometry for domain statements.

  • Forced with runoff, not with weather. Worth restating because it is unusual: GloFAS Seasonal takes downscaled runoff from SEAS5, whereas the medium-range chain takes meteorological fields. The land surface partitioning is therefore partly SEAS5's rather than LISFLOOD's, which matters for anyone comparing the seasonal and medium-range products as though they were the same model at different ranges.

  • Discharge accumulation semantics. River discharge in the last 24 hours is a daily mean over the preceding window, not an instantaneous value at the timestamp.

  • No control/perturbed split. Unlike the medium-range dataset, this one has no product_type selector in the request form. If the control member is needed separately, it must be identified from the ensemble dimension after retrieval.

  • Relationship to other CEMS-Flood datasets. Medium-range sibling: GloFAS Forecast. European counterpart at 1 arcminute: EFAS Seasonal. The seasonal hindcast archive (cems-glofas-seasonal-reforecast) and the ERA5-forced historical simulation (cems-glofas-historical) are historical-only and out of scope as standalone entries.

  • AI relationship. The AIFS Single forcing introduced at GloFAS v4.4 applies to the medium-range chain out to 15 days. This seasonal product is forced by SEAS5 and is not AI-influenced on current evidence. If that changes, update AI_MODELS.md.

  • Not a flood warning. The licence states that CEMS-Flood data does not constitute a flood warning, which only national and regional institutions are authorised to issue.

Recent version history

Shares the GloFAS operational versioning chain — see GloFAS Forecast for the full sequence. Points specific to the seasonal product:

  • v4.3 — 4 June 2025: CEMS-Flood long-range product design harmonised across EFAS and GloFAS (EFAS from v5.4, 12 March).
  • v4.0 — 26 July 2023 (major): seasonal forecasts updated to the newly calibrated higher-resolution hydrological model; resolution 0.1° → 0.05°.
  • June 2021: forecast length extended from 123 to 215 days.

Full chronology: https://confluence.ecmwf.int/display/CEMS/GloFAS+versioning+system

Official documentation