GloFAS Rapid Risk Assessment
The rapid risk assessment (RRA) product aims to provide emergency response actors daily updates of predicted
flood impacts on population, sensitive infrastructures and urban areas. The procedure combines GloFAS flood
forecasts with event-based rapid flood mapping, translating the predicted river flows into explicit flood
In GloFAS, the flood impact forecasts are based on three components: 1) medium-range flood forecasts, 2)
event-based rapid flood mapping, and 3) impact assessment.
- Medium-range flood forecast: every time a flood event is forecasted in GloFAS , the
magnitude of the
forecasted peak discharge (based on the ECMWF-ENS GloFAS ensemble forecast median for the full
forecasting period) is compared against the estimated local flood protection levels. River grid cells
which meet following criteria are selected for following steps of the procedure:
- upstream area greater than 5,000 km2
- peak discharge is greater than 10-year return period threshold
- estimated protection levels are exceeded.
Rapid flood mapping: for each GloFAS 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 0.00833 degree (~1 km) and is shown on the “Rapid Flood Mapping” layer.
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 (health, education, airport facilities) and land cover. Information on
potential impact is aggregated over Global administration regions which are shaded according to the
impact matrix which combines the total population exposure to the flood hazard with the lead time of the
At present the information in the Rapid Impact Assessment and Rapid Flood Mapping layers are experimental.
Care should be taken when interpreting the population affected as the procedure only considers the total
number of people living within the flood inundation footprint and it does not consider their vulnerability
nor their ability to evacuate. Therefore the affected population values can sometimes be higher than the
actual number of people reported as being affected.
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,
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,