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 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. They are organised in four categories:

  • Reporting points: points in the river network highlighted because their flood forecast probability meets reporting criteria. Two threshold levels are used: 2-year return period (2yr RP) and 5-year return period (5yr RP)
  • Threshold Level Exceedance: reporting points showing the maximum flood threshold level expected to be exceeded the day of the forecast date (ongoing); within the next 1-2 days (1-2 days); within next 3-5 days (3-5 days); beyond day 6 (>5 days).
  • Flood probability: model cells of the river network where there’s probability of exceeding the 5-yr return period threshold level within (< 48h) or after (>48h) the next 48 hours. The probability is calculated based on the ECMWF-ENS EFAS forecast.
  • Real-time Hydrographs: for selected points where near real-time river discharge is available to EFAS, level of probability exceeding an average yearly maximum discharge within the next 10 days. The probability is calculated based on post-processing of the ECMWF-ENS EFAS forecast and observed discharge

Extra local information associated with each flood forecast product is available from the map viewer as pop-up plots, except for the ‘Flood Probability’ product. They include flood hydrographs, persistence diagrams and summary diagrams of catchment meteorological forcings.

EFAS medium-range flood forecast products are displayed as colour coded overview maps. They can be viewed under the ‘Flood Summary’ category of the Map Viewer. 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), and the ‘Rapid Flood Mapping’ and ’Rapid Impact Assessment’ layers.

Reporting points

Pop-up plots display reporting points information, such as:

  • Point geographical information: country, basin, river, station name, etc.

  • Forecast summary: forecast issue date, probability value and tendency2 and time to peak.

  • Discharge hydrographs

  • Catchment meteorological forcings

  • Persistence 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. For ensemble forecasts, the forecast probability to exceed a given threshold is also shown.

  • Real-time hydrographs (for certain points only): ECMWF-ENS EFAS forecast post-processed based on observed discharge. It also displays the probability of exceeding an average yearly maximum discharge within the next 10 days
     

    Flood Probability

     

    Treshold

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. 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.