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. The impact is calculated by combining the flood severity and probability with the exposed population. The result is summarised on administration units sourced from NUTS.

The EFAS flood impact forecasts are provided to the users as a set of dedicated layers described in EFAS Rapid Flood Mapping and Rapid Impact Assessment.