The EFAS medium-range flood forecasts provide an overview of flood probability over the coming 10 days. They are created by comparing the EFAS forecast simulations with EFAS flood threshold levels. These flood threshold levels are calculated for every grid cell, based on a discharge time series simulated by the operational LISFLOOD hydrological model from observed meteorological data.
EFAS medium-range flood forecast products are displayed as colour coded overview maps and time series information at reporting points that can be viewed under the ‘Flood Summary’ layer of the mapviewer. There are five main products:
- The ‘Reporting Points’ layer (from 8th October 2019; explained below).
- The ‘Flood Probability’ layers (explained below).
- The ‘Threshold level exceedance’ layers (explained below).
- The ‘Rapid Flood Mapping’ and ’Rapid Impact Assessment’ layers.
Additional local information associated with each flood forecast layer (except for the ‘Flood Probability’ layers) is available from the mapviewer as pop-up plots. They display information such as:
Point geographical information - e.g. country, basin, river and station name.
Forecast summary - e.g. forecast issue date, probability value and tendency and time to peak.
Summary diagrams of catchment meteorological forcings.
Consistency diagrams: show the evolution of the forecast signal over time. They display the forecast threshold exceedance for each return period threshold (1.5-, 2-, 5-, 20-year) for each day of the forecast horizon for the latest eight consecutive forecast runs.
Real-time hydrographs (for certain points only): ECMWF-ENS EFAS forecast post-processed based on observed discharge. They also display the probability of exceeding a mean annual maximum discharge within the next 15 days.
N.B. EFAS medium-range flood forecasts produced at least 30 days earlier are freely available to view. Real-time EFAS medium-range flood forecasts are only available under certain conditions. Visit the EFAS data access pages to learn more on data restrictions.
1For each NWP-driven forecast, a flood probability is computed for each flood threshold using the maximum forecast discharge value over the 10-day forecast horizon. A total probability of exceedance is then computed from these maximum forecast probabilities (from DWD-HRES, ECMWF-HRES and ECMWF-ENS, with global weights associated with each forecast. N.B. for dynamic reporting points COSMO-LEPS is currently not used). Dynamic reporting points are finally created (and their alert levels are computed) based on the following rules:
5-year return period: total probability > 15% and upstream area > 2000 km2
2-year return period: total probability > 50% and upstream area > 2000 km2
Alert levels are also computed for static reporting points where hydrological metadata information is available. The rules are different for these points:
5-year return period: total probability > 10% or at least 3 COSMO-LEPS members exceeding the 5-year return period threshold, and upstream area > 1000 km2
2-year return period: total probability > 10% and upstream area > 2000 km2
Alert levels are only computed for reporting points with past persistent forecasts.