Deadly 2021 Floods Exposed Major Gaps in Hazard Maps, Study Finds

The catastrophic July 2021 floods that killed more than 200 people in Germany and Belgium exposed serious gaps in official flood hazard maps, according to a new study in the journal Earth's Future. Researchers from the University of Potsdam, the Helmholtz Centre for Geosciences, the University of Louvain and Johns Hopkins University analyzed the circumstances of 224 deaths caused by the floods, which followed heavy rain from the low-pressure system "Bernd" across North Rhine-Westphalia and Rhineland-Palatinate in Germany and the Walloon region of Belgium. More than half of the deaths occurred in Ahrweiler county in Rhineland-Palatinate.

About 50% of the deaths in North Rhine-Westphalia and 75% in Rhineland-Palatinate occurred outside the zones that official maps had marked as at risk even under an extreme flood scenario. "Consequently, the available flood hazard maps were not sufficient to adequately illustrate the risks to the public," said lead author Annegret Thieken of the University of Potsdam's Institute of Environmental Science and Geography.

The study also found gaps in how safety guidance was communicated. In North Rhine-Westphalia, 14 people died while trying to reduce damage, such as checking pumps or starting cleanup in flooded basements. Across the three regions, 81 people died on the ground floor or upper floors of homes that should have been evacuated in time, and further deaths were linked to flooded or collapsed bridges and vehicles that were swept away or stranded.

People over age 60 were significantly overrepresented among the victims, accounting for 72% of deaths, and in Rhineland-Palatinate, 12 people died in a flooded residential home for adults with mental disabilities. Thieken said warning messages need to clearly state when evacuation from flood-prone areas is still possible, and when the safer option is instead to move to an upper floor.

The researchers are calling for a revision of the European Floods Directive to better account for worst-case flood scenarios in hazard mapping, risk management and communication.