EFAS provides different flash flood indicators based on two main concepts: 1) ERIC, generated from high-resolution numerical weather predictions with a lead time of up to 120 hours, and 2) radar-based products with a lead time of between 3-120 hours depending on the product.

ERIC - Numerical weather prediction based flash flood indicator

The ERIC flash-flood method is described in ERIC flash flood forecasting.

Two ERIC products exist:

  • Reporting points  (“ERIC Reporting Points” layers): points in the river network (where the catchment area is <=1000 km2) where flash flooding is possible. Enlarged triangles highlight where the flash flood forecast probability over the next 5 days meets certain criteria:

                      1. probability of exceeding a 5 year return period magnitude of the surface runoff index is forecasted to be greater than or equal to 30%

                      2. lead time of the above criterion being satisfied is <= 48 hours in a region for which an EFAS partner exist

     

  • Affected area  (“ERIC Affected Area”): river network which contributes to each ERIC reporting point, i.e. areas at risk from flash flooding (“ERIC Affected Area”)

Radar-based Flash Flood Products

Seven radar-based flash flood products are available on the EFAS website, please note that these products are experimental and are not operationally supported, meaning outages in the products' availability are possible:

  • Radar Coverage which shows the area covered by the pan-European OPERA radar composite. New data are generated every hour
  • Radar-based rainfall products:
    • Radar-based Accumulated Precipitation 80th Percentile: shows the 80th percentile from the ensemble of forecasted accumulated precipitation at 2-km spatial resolution. Accumulated precipitation in the first 0-6 hours of the lead time range are shown every 1-hour and are produced by blending the ensemble radar nowcast data with the ECMWF ensemble forecast. For lead times from 6-120 hours, the accumulated precipitation is shown every 6 hours and is generated only from the ECMWF ensemble forecast. New forecasts are generated every hour.
    • Radar-based Previous 24-h Accumulated Precipitation: the total accumulated precipitation over the previous 24-hours at 2-km spatial resolution. Created by a spatial blending of the radar observations and short range ECMWF forecasts from the control member. The data are only updated at 00 and 12 UTC each day.
  • Radar-based river flash flood products:
    • Radar-based River Flash Flood Impact: highlights 1-arcminute (~1.4 km) river grid cells (where the catchment area is <=1000 km2) where there is a risk of impacts caused by riverine flash flooding. Data are shown at 1-hour time step for the first 6-hours of lead time, they are shown at 6-hourly time steps thereafter until a maximum lead time of 120 hours. New forecasts are generated every hour.
    • Radar-based River Flash Flood Impact Catchment Summaries (0-120h): shows river catchments (with a drainage area <=1000 km2) where impacts due to riverine flash flooding are possible. The catchments summarise the 90th percentile of the maximum impact predicted in any 1-arcminute grid cell during lead time ranges of 0-6, 7-24, 25-48 and 49-120 hours. New data are generated every hour.
  • Radar-based urban flash flood products:

Legacy Products: ERICHA - Radar-based precipitation monitoring and nowcasting flash flood indicators

Please note that since EFAS v5.1 (2024-03-21) these products are no longer produced operationally and are no longer shown on the EFAS web interface. The documentation has been retained for reference.

The ERICHA flash-flood method is described in ERICHA flash flood nowcasting.

Three ERICHA products exist:

  • Hourly precipitation maps : Hourly precipitation totals from the  OPERA  radar composite, updated every 15 minutes (“ERICHA hourly accumulation precipitation” layer).
  • Flash flood hazard maps : Sections of the river network highlighted because their flash flood forecast probability over the next 4 hours meets certain criteria. The thresholds are based on regional climatic characteristics and river basin upstream area as published by the  MeteoAlarm  consortium (“ERICHA - FF hazard levels forecasts” layer).
  • Daily precipitation maps : Daily gauge-adjusted radar rainfall accumulation over the last 24 hours ("ERICHA 24-h accumulations" layer).

For more information

Alfieri, L., Thielen, J., 2015: A European precipitation index for extreme rain-storm and flash flood early warning. Meteorol. Appl., 22(1), 3–13,  doi:10.1002/met.1328

Berenguer, M., Sempere-Torres, D., Pegram, G.G.S, 2011: SBMCast - An ensemble nowcasting technique to assess the uncertainty in rainfall forecasts by Lagrangian extrapolation. Journal of Hydrology 404 (3-4), 226-240,  doi:https://doi.org/10.1016/j.jhydrol.2011.04.033

European Rainfall-InduCed Hazard Assessment system (ERICHA) -  http://www.crahi.upc.edu/ericha/index.php?option=com_content&view=article&id=44&Itemid=29&lang=en

Fundel, F., Walser, A., Liniger, M.A., Frei, C., Appenzeller, C., 2010: Calibrated precipitation forecasts for a limited-area ensemble forecast system using reforecasts. Monthly Weather Review, 138(1), 176-189,  https://journals.ametsoc.org/doi/10.1175/2009MWR2977.1

Park, S.; M. Berenguer, and D. Sempere-Torres, 2019: Long-term analysis of gauge-adjusted radar rainfall accumulations at European scale. Journal of Hydrology, 573, 768–777,  https://doi.org/10.1016/j.jhydrol.2019.03.093

Raynaud, D., Thielen, J., Salamon, P., Burek, P., Anquetin, S., Alfieri, L., 2015: A dynamic runoff co-efficient to improve flash flood early warning in Europe: Evaluation on the 2013 central European floods in Germany. Meteorological Applications, 22(3), 410–418,  doi:10.1002/met.1469