Mid July 2021 floods in Western Europe

In mid-July catastrophic floods ravaged Western Europe, causing more than 180 casualties and large material damage in Germany and Belgium, and to a lesser extent, in parts of the Netherlands, France, Luxembourg and Switzerland.

From a meteorological point of view, the event was the consequence of a slow-moving low-pressure system that insisted over Western Europe for several days, leading to persisting and intensive rainfalls. Starting from July 14, these heavy precipitations resulted in severe flooding of urban areas in small and large river basins.

In Germany, the most affected Länder were the North Rhine-Westphalia and the Rhineland-Palatinate, particularly the small and steep basin of the Ahr River (900 km2) where the majority of fatalities and damages occurred.

Regarding forecasts, meteorological and hydrological modeling had already predicted severe events over large areas of central Europe a few days in advance. Indeed, forecasts on July 9 and 10 from the European Flood Awareness System (EFAS) indicated a high probability of flooding for the Rhine River basin affecting Switzerland and Germany, and then a high risk of flooding for the basin of the Meuse River in Belgium. The first EFAS notifications for the Rhine were sent to the competent national authorities on July 10, and for the Meuse from July 12. The first formal notifications for flash floods in western Germany were spread on July 13.

Likewise, the German Federal Meteorological Service (DWD, www.dwd.de) issued a weather alert for July 14-15 predicting extensive precipitation. However, the prediction of the effects on the ground, entrusted to each Länder in Germany, was only partially able to seize the extension and type of the phenomenon in the small and steeper basins.

Critical issues emerged not only regarding impact forecasting, but also coordination and communication among different institutions and to citizens, like transmitting alerts to regional and local authorities and translating warnings from flood forecasters into instructions to citizens in danger.

Floods in Western Europe highlighted the importance of a coordinated action of all the stakeholders involved in the early warning system, where all the elements (disaster risk knowledge, monitoring and forecasting, dissemination and communication, preparedness and response) are fundamental to deliver timely warnings and enact early action. This is particularly relevant for small river basins, which react very quickly to precipitation and where communications should be accompanied by a proper preparation of the local communities on how to respond during an event.

A community based early warning system, standard operating procedures to link early warning to early action through local preparedness and response plans and an improvement of the coping capacity of all institutions are the keys to reduce the flood risk and to adapt to climate change.

Other references:

  • German flood alerts: https://www.hochwasserzentralen.de/ (federal portal); hochwasser-rlp.de; http://fruehwarnung.hochwasser-rlp.de/ (Rhineland-Palatinate); https://luadb.it.nrw.de/LUA/hygon/pegel.php?karte=nrw (North Rhine-Westphalia);
  • EFAS on July floods: https://www.efas.eu/en/news/faq-efas-and-recent-flood-events
  • DWD report:
  • https://www.dwd.de/DE/leistungen/besondereereignisse/niederschlag/20210721_bericht_starkniederschlaege_tief_bernd.pdf;
  • Civil protection system BBK: https://www.bbk.bund.de/DE/Das-BBK/Das-BBK-stellt-sich-vor/Das-deutsche-Bevoelkerungsschutzsystem/das-deutsche-bevoelkerungsschutzsystem_node.html;jsessionid=2AAE6D727ED5A03B9C5F1DA66F681ED5.live361