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 5 days, and 2) ERICHA, based on radar-based precipitation monitoring and nowcasting for the next 6 hours.
ERIC - Numerical weather prediction based flash flood indicator
The ERIC flash-flood indicator is generated by comparing the forecasted surface runoff accumulated over the upstream catchment with a reference threshold. It is based on the 20-member COSMO-LEPS ensemble precipitation and soil moisture forecasts from the LISFLOOD hydrological model and provides indicators for the next 5 days for catchments smaller than 2,000km2.
Two ERIC products exist:
Reporting points (“ERIC Reporting Points” layers): points in the river network (where the catchment area is <= 2000 km2) where flash flooding is possible. Enlarged triangles highlight where the flash flood forecast probability over the next 5 days meets certain criteria:
probability of exceeding a 5 year return period magnitude of the surface runoff index is forecasted to be greater than or equal to 30%
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”)
ERICHA - Radar-based precipitation monitoring and nowcasting flash flood indicators
The ERICHA flash-flood indicator is generated from radar-based precipitation monitoring and nowcasting product, based from the European OPERA radar composite. This aims to capture very localised events difficult to predict from numerical weather prediction systems, but only provide information up to 4 hours.
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