Page History

Image Modified

The following is a description of GloFAS v4.0, available as pre-release on the GloFAS Stage Platform from 05 July 2023 and fully operational GloFAS from 26 July 2023.

the latest operational release of GloFAS v3.2. For an overview of other GloFAS releases, please see : GloFAS versioning system.

Summary

GloFAS version 3.2 was implemented as a minor change to provide access to the Global Flood Monitoring (GFM) beta version through its web interface (www.globalfloods.eu). 

The  Global Flood Monitoring (GFM) is designed to provide a continuous global, systematic monitoring of flood events, with significantly enhanced timeliness of flood maps for emergency response and improved effectiveness of Rapid Mapping activation requests (through better identification of the area of interest). The  beta version contains flood products that are based on an ensemble approach integrating three robust, cutting edge algorithms developed independently by three scientific teams. The data processing architecture underlying the different scientific algorithms is based on the data cube concept, whereby SAR images are geocoded, gridded, and stored as 'analysis-ready data' (ARD) in an existing spatio-temporal SAR data cube. Users have access to consensus flood maps (Observed Flood Extent layer) where a pixel is marked as flooded when at least two algorithms classify it as water.

Here is a summary of the main changes to the GloFAS web service:

• Introduction of near real-time flood mapping-related products from the Global Flood Monitoring (GFM) beta version including:
  • S-1 Observed Flood Extent (data format: raster (GeoTIFF) and vector (shapefile)). The layer i dentifies the pixels covered by floodwater. Pixels that are usually underwater (such as lakes and reservoirs) are identified based on the monthly Sentinel-1 Reference Water Mask are not part of the Sentinel-1 Observed Flood Extent.
  • S-1 Observed Water Extent (data format: raster (GeoTIFF) and vector (shapefile)). The layer i dentifies the pixels classified as open and calm water using Sentinel-1 SAR backscatter intensity and is derived using the ensemble flood mapping algorithm.
  • Exclusion Mask (data format: raster (GeoTIFF)). The layer i ndicates the pixel locations where the SAR data could not deliver the necessary information for a robust flood delineation. It combines static effects leading to no-sensitivity in flood mapping, water-look-alikes, strong typography, and radar shadows.
  • Uncertainty Values (data format: raster (GeoTIFF)). The layer is g enerated along with the binary map product as a simplified appraisal of trust in the ensemble flood extent detection approach.

• Introduction of reference products from the Global Flood Monitoring (GFM) beta version including:
  • S-1 Reference Water Mask (data format: raster (GeoTIFF) and vector (shapefile)). The layer i dentifies the pixels classified as open and calm water, both permanent and seasonal, using Sentinel-1 SAR backscatter intensity using an ensemble flood mapping algorithm.
  • Affected Population layer (data format: raster (GeoTIFF)). The layer is extracted from the Global Human Settlement (GHS) layer and from the GHS-POP dataset. Represents the estimate of the number of people affected by the flood.
  • Affected Land Cover layer (data format: raster (GeoTIFF)). The layer provides information for quick assessment of affected land cover or land use types, e.g., how much agricultural/cropland area is affected by the flood extent.

• Introduction of new data access functionalities, including: 
  • Function to define Area of Interest.
  • Visualization of the available products for user-defined AOIs.
  • GFM products download option for user-defined AOIs (per layer or for all product layers).
  • Notifications configuration via the app and/or Twitter.

  Key specifications of the products

Input satellite data

Satellite sensor

S-1 - Synthetic Aperture Radar (SAR)

Acquisition mode

Interferometric Wide Swath (IW)

Data product

Level-1 - Ground Range Detected (GRD)

Spatial sampling

20 x 22 m

Global revisit frequency

Europe: ~1-3 days. Rest of the world: ~3-14 days, depending on location

SAR polarization scheme

VV + VH

General product specifics

Geographic coverage

Global

Pixel size

20 m

Timeliness

<8 hours after S-1 image acquisition.

Thematic accuracy

Target threshold of >70-80%, based on the Critical Success Index

v4.0 introduces a number of major changes to the system, including:

• higher spatial resolution. GloFAS v4.0 has 0.05 degrees resolution (~5km), as opposed to all the previous GloFAS versions having 0.1 degrees resolution (~10km).
• an entirely new set of 0.05 degrees resolution input maps produced using the most recent research findings, remote sensing, and in-situ datasets.
• major improvements to the open-source hydrological model LISFLOOD.
• a new hydrological model calibration at 1995 in-situ gauging stations. Furthermore, a parameter regionalisation was performed to estimate the parameters of catchments for which in situ discharge observations were not available.
• new return period thresholds and snow water/soil moisture anomaly maps based on a climatology from 1980 – 2022. The GloFAS v4 river discharge climatology is available at the C3S Climate Data Store.
• updated GloFAS Seasonal forecasts using the newly calibrated, higher resolution hydrological model.
• Increased spatial resolution from 1km to ~90m (3 arc secs) for the flood hazard maps used in the GloFAS rapid flood mapping and impact assessment

This major version change is associated with an update of the historical hydrological reanalysis. 

This upgrade of GloFAS has large impacts on the GloFAS modelling results.

31 stations were also added to the reporting point: 9 stations in Canada, 7 stations in Russia, 4 stations in Finland, 3 stations in Argentina and 1 station in each of Brazil, United States, Morocco, Benin, Uganda, Thailand, Columbia and South Africa.

Technical details