Flood impact forecasts are especially important in the preparedness phase, to support the planning and allocation of rescue assets, and to get a first estimate of the forecasted flood event’s potential socio-economic consequences.

In EFAS, the flood impact forecasts are based on three components: 1) medium-range flood forecasts, 2) event-based rapid flood mapping, and 3) impact assessment.


  1. Medium-range flood forecast: every time a flood event is forecasted in EFAS , the magnitude of the forecasted peak discharge (based on the ECMWF-ENS EFAS ensemble forecast median for the full forecasting period) is compared against the local flood protection levels. River grid cells where the protection levels are exceeded are selected for the following steps of the procedure.
  2. Rapid flood mapping: for each EFAS river section identified in step 1, flood prone areas are delineated, using a catalogue of flood hazard maps. The obtained event-based hazard map has a spatial resolution of 100 by 100 m and is shown on the “Rapid Flood Mapping” layer.
  3. Impact assessment: the event-based hazard maps are combined with exposure information to assess regional impacts (shown on the “Rapid Impact Assessment” layer). Considered exposure includes population, infrastructure and land cover.


rapid flood mapping product

Example of Rapid Flood Mapping product

rapid impact assessment example

Rapid Impact Assessment example

During large-scale flood events, EFAS impact forecasts can be used to pre-task the acquisition of satellite images for a possible activation of the rapid mapping component of the Copernicus EMS.

For more information

Dottori, F., Kalas, M., Salamon, P., Bianchi, A., Alfieri, L., and Feyen, L., 2017: An operational procedure for rapid flood risk assessment in Europe, Nat. Hazards Earth Syst. Sci., 17, 1111-1126, https://doi.org/10.5194/nhess-17-1111-2017

Alfieri, L., Salamon, P., Bianchi, A., Neal, J., Bates, P.D., Feyen, L., 2014. Advances in pan-European flood hazard mapping, Hydrological Processes, 28 (18), 4928-4937, https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.9947