Flash flood notifications are issued for administration regions, these regions are defined by merging NUTS level 2 and 3 data from EUROSTAT 2016 and GADM data and can be viewed on the EFAS web viewer under Static > Administrative regions. EFAS partners will receive an email flash flood notification when the following criteria are met:

  • Administration region is covered by an EFAS Conditions of Access (CoA) i.e. there is an EFAS partner present
  • Probability of the flash flood return period (shown by the ERIC reporting points layer) exceeding the 5 year threshold is >= 30%
  • Lead time to the event is <= 48 hours

The flash flood notifications are derived from the ERIC Reporting Points layer on EFAS which is under the Flash Flood layers heading. If an ERIC reporting point satisfies the criteria above, it is displayed as an enlarged triangle (Fig 1). However, only one enlarged triangle is shown within each administration region, if multiple points satisfy the flash flood notification criteria then the following checks are made:

  • Identify the point with the earliest lead time
  • If multiple points have the same lead time, select the point with the great exceedance probability of the 5 year flash flood return period threshold

Figure 1. Triangles show the ERIC reporting points, large triangles show locations where flash flood notifications would be issued. Dark blue lines show the administration region boundaries.

Flash Flood Notification Email

Twice per day, the EFAS forecaster from the dissemination centre will analyse the ERIC Reporting points layer from the latest forecast and will identify the locations, shown by the enlarged triangles, where flash flood notifications should be issued. Typically one flash flood notification email is sent per administration region, however if multiple neighbouring regions have enlarged triangles, then a single notification email will be issued which covers all the affected regions.

The flash flood notification email contains the following information:

Section 1: Notification Details

This section contains information about the locations, magnitude and timing of the forecasted flash flood event

  • Country(ies): lists the countries where flash flooding is forecasted to occur
  • Administration Region(s): lists the administration regions where flash flooding is forecasted to occur
  • Time of peak within next 48 hours: this shows the time within the next 48 hours when the maximum forecasted flash flood value is expected to occur. If flash flooding is forecasted in multiple administration regions, then the earliest time is recorded
  • Probability to exceed a 5-year flash flood return period threshold: this is the probability to exceed the 5-year flash flood return period threshold based on the 20 ensemble member forecast from the COSMO-LEPS model. Note that the return period threshold is derived from modelled values of the ERIC flash flood indicator using an 18 year COSMO-LEPS historical reforecast period, therefore these return period thresholds are not comparable with return period thresholds derived from observational records at gauging stations. 
  • Probability to exceed a 20-year flash flood return period threshold: as above but for the 20-year flash flood return period threshold.
Section 2: Additional Information
  • Notification based on Forecast: shows the date and time of the forecast which was used to create the flash flood notification email
  • Affected area susceptible to landslides: reports the total area (km2) across all the affected administration regions which lie within Moderate, High and Very High landslide susceptibility categories. The landslide susceptibility categories are defined according to pan-European maps of topography, geology and soil type. These categories are intersected with the flash flood forecasts by identifying the upstream area for each reporting point which satisfies the flash flood notification criteria and then summarising the total area (km2) of each Moderate, High and Very High landslide susceptibility category.
  • Forecaster comments: this can be used by the EFAS forecaster to add any additional comments about the flash flood forecast situation