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Flood hazard icon Floods

ADAM monitors floods globally, combining forecast-based alerts (GLOFAS) with satellite-derived flood mapping after an event. Long-duration events are monitored weekly for up to one month.

Data sources

Forecast side:

  • GLOFAS — Global Flood Awareness System (JRC) and GeoGLOWS: river discharge forecasts at gauge points, with trend and return-period probabilities
  • ECMWF — 5-day precipitation forecast

Observation side:

  • NOAA VIIRS — daily satellite flood detection used for the observed flood extent
  • GPM IMERG — past accumulated rainfall
  • JRC surface water — permanent and seasonal water bodies, to separate flooding from normal water
  • Copernicus EMS, FLOODSCAN, CSDMS — complementary rapid mapping and flood observatories
  • GEE / GCS — Google Earth Engine compute for satellite-derived mapping

Impact figures use a global population grid and cropland masks aggregated on GAUL administrative units. Flood products are produced in partnership with the JRC and FloodList.

What ADAM produces

  • Flood forecast bulletin — one page: rainfall and river flood forecast for the next 7 days, populated places of concern with the forecast day of peak flow
  • Flood event report — two pages: satellite-observed flooded area with a rapid impact summary, then population and cropland affected aggregated by district
  • Map layers — flood alerts, flood events, GLOFAS gauge forecasts and seasonal outlooks as API collections

Both PDFs are described page by page in Dashboards & Products. Flood impact analyses can also be run on demand for an area requested by a Country Office; they appear in the same collection with the source ADAM Floods On-Demand.

How to read the outputs

Forecast versus observation. A forecast alert says that a river is expected to exceed a flood threshold in the coming days, at a given probability; nothing has happened yet. An impact analysis maps water that a satellite has actually seen on the ground. The Live Map uses two different symbols for them, and the collections are separate in the API.

Return periods. River forecast points show the probability of exceeding the 2, 5 and 20 year return period discharge. A 2-year flood is frequent and usually manageable; a 20-year flood is rare and damaging. The trend arrow and the day of peak tell you whether the situation is still building and when it will culminate.

Confidence of the observed extent. Optical satellite detection cannot see through clouds, so the flooded area can be underestimated during the rain itself and is more reliable in the days after. The daily revisit of VIIRS means a footprint reflects a specific day; long events are re-analysed weekly. Pixels are classed as partly, moderately or highly flooded by the share of water they contain, and permanent water is masked out.

Exposure is not damage. People and cropland inside the flooded pixels are exposed, not necessarily harmed. Cropland impact depends on the crop calendar, and buildings are only counted where data exist.

Typical alert workflow

  1. A GLOFAS forecast crosses a threshold and a forecast bulletin is issued
  2. After flood onset, satellite mapping produces the first impact analysis, usually within 72 hours
  3. Impact figures by district are published and alerts are sent for the areas concerned
  4. For prolonged events, the analysis is repeated weekly for up to one month

Next steps