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After the Flood – what can be learned from reconstruction in the flooded areas along the Ahr and Erft rivers

The researchers of the KAHR project are investigating what lessons can be learned from the flood of the century and how such devastating damage can be avoided in the future.
Photo : Philipp Bubeck
The researchers of the KAHR project are investigating what lessons can be learned from the flood of the century and how such devastating damage can be avoided in the future.

In July 2021, parts of Rhineland-Palatinate and North Rhine-Westphalia experienced one of Germany's most severe natural disasters after 1945. The floods on the Erft, Ahr, Inde, Vicht, and Wupper rivers claimed the lives of more than 180 people and caused damage of over 30 billion euros. Environmental scientist Phillip Bubeck recently visited the flood zone on the Ahr River. “In the center of Bad Neuenahr-Ahrweiler, the damage is still clearly visible,” he says. “You can see the remains of the destroyed bridges and the temporary makeshift bridges. Only a few stores are open. Many buildings have been marked by the water and are nailed up with plywood. We are far from normal.” But the researcher also saw that reconstruction was progressing in many places. “Many streets have been repaired and redone, and one pizzeria had put up a sign on which the mayor congratulated it on its reopening.”

Philip Bubeck is environmental scientist at the University of Potsdam and member of an interdisciplinary research consortium initiated by the German Federal Ministry of Education and Research a few months after the flood. In the KAHR research project – Climate Adaptation, Flooding, Resilience – 13 institutions support reconstruction in the disaster area. Their expertise in water management, spatial and urban planning, and social sciences is being used to review and reappraise the events. It is expected to lead to new concepts for better risk management and protection in flood risk areas.

Psychosocial consequences still inadequately researched

“We know very little about how reconstruction works or about the psychosocial consequences of such a disaster,” Bubeck explains. He and his colleagues are using questionnaires to try to find out more about what is going on in the minds of the affected people and how they cope with what they have experienced. What damage did private households and businesses sustain? How high was the water? Was it polluted? How did people try to protect themselves, and will they take precautions for the future? “Such severe events put an enormous psychological strain on people, which can last for years,” he knows. Mental health is therefore one of the team’s research priorities – especially since the data on this to date is sparse. The researchers want to create hotspot maps based on the survey results that show where there is the greatest need for support.

Prof. Dr. Christian Kuhlicke, urban and environmental sociologist at the Helmholtz Centre for Environmental Research (UFZ) in Leipzig and Professor for Sustainability and Environmental Risks at the University of Potsdam, also concentrates on the local actors. “From the level of neighborhoods to the municipalities to the state, from the mayor to companies to spatial planning and water management: More than 200 actors are involved in reconstruction,” he explains. He is interested in how reconstruction is being shaped and what factors are significantly influencing the nature of reconstruction. Who makes which decisions, which interests prevail, and what factors influence this? In the pilot communities of Stollberg, Eschweiler, and Bad Neuenahr-Ahrweiler, he is primarily looking at social facilities such as schools, libraries, swimming pools, or inns. “We support reconstruction, but also try to observe the process as comprehensively as possible,” Kuhlicke says.

The process of repair and starting over again can reveal a lot about which levers have an effect. Political and legal frameworks, financial support, but also cultural patterns shape the process and can regulate it. “There was a one-time ‘whoosh’ and now we will have peace for the next few decades.” That’s how Kuhlicke describes the mood of many locals. People then often rebuild exactly as it was before - with all the known risks. Also because time is tight, and things have to be done quickly. Temporary shelters, which provide those affected with everything they need, could ease the pressure somewhat and create more space for the necessary search for new solutions.

The researchers want to learn from their observations and analyses how things can be done differently to strengthen the resilience and sustainability of communities. They will pass on their findings to state and federal political stakeholders and municipalities, ultimately to derive recommendations on how to better respond locally and in the future, and how to prepare for future disasters because the threat of flooding is here to stay.

Rethinking flood protection

Does such an extreme scenario impend every 1000, every 100 or every ten years? That’s what Professor Bruno Merz, a hydrologist at the German Geosciences Center (GFZ) and Professor of Engineering Hydrology and Management of Geohazards at the University of Potsdam, is trying to find out. “It was a very unusual event,” he says about the recent flood. There were very heavy rainfalls in a short period of time, at the same time saturated soil that could hardly absorb water and an unfavorable topography: Water was able to run quickly off the steep slopes, collect in the narrow valleys, build up an enormous flood wave and run off with destructive power. “95% of all flood events proceed differently, but it’s precisely these rare, special events that we need to understand better,” Merz emphasizes. That’s why we need to rethink flood protection and take such scenarios into account.

Bruno Merz provides the necessary data for this – with the help of a weather generator and a model chain. “Our weather generator is a model that generates weather artificially,” Merz explains. Based on past and present weather data, the researchers simulate the weather for 10,000 years in the three heavily affected river basins of the Ahr, Erft, and Rur with a resolution of one hour. The researchers feed the data into a chain of additional models that depict water discharge in the impacted areas, flood areas, and the resulting damage.

“We generate huge amounts of data with this model chain, from which we extract rare, extreme flood events. This allows us to better assess what could happen in the region in terms of flooding and possible damages,” Merz says, explaining the goal of the calculations. In the next step, the research team will extend the model to other areas and include climate change. “Many studies show that heavy rainfall events have already increased, and climate models predict the same for the future,” Merz says. In the coming decades and centuries, flooding could become a more frequent and severe event in many areas.

Understanding extreme events and their consequences better

All this raises some new questions for flood protection authorities that are not easy to answer. Together with the German Weather Service, state ministries, water associations, and the environmental agency of the federal state, Merz’s team is part of a working group in North Rhine-Westphalia. They are evaluating the currently valid flood statistics to determine whether they are outdated and need to be adjusted with new data. For all river basins in Germany, there are calculations about the kinds of floods that can be expected every 100 years. Strict regulations apply to the flood zones determined from these calculations. For example, they may not be redeveloped. Do the assessment values now have to be increased? And if so, how much? “This is not an easy discussion,” Merz emphasizes. This has a major impact on flood hazard maps and flood protection measures such as dams or dikes, but also on the development plans for the affected areas. The results from the modeling should provide more clarity.

With fast computer models and big data sets, more will be possible in flood forecasting than has been until now, Merz is convinced. Currently, forecasts and warnings provide water levels at specific river gauges. But mathematical models can also provide area-wide information on potential flooding and calculate what water levels and depths, flow velocities, and damage to buildings or bridges can be expected for areas far from the forecast gauges. They can “take the established warning system to the next level,” Merz explains.

At the end of the KAHR project, which is funded until 2024, the three researchers hope to have a more accurate picture not only of the material damage and social impact the flood caused in Rhineland-Palatinate and North Rhine-Westphalia, but also how to bring together the necessary actors to deal with the crisis, how to better communicate the risk, to get the warnings to people in time, and to better manage reconstruction. Different expectations and interests often collide in this process. “People are often preoccupied with very practical problems,” Bubeck says. “Where can I get a craftsman and building materials?” At the same time, the authorities have to manage the crisis as a whole and to set the course. “Of course, the water industry looks at it very differently than an affected private individual or the operator of a social institution,” Kuhlicke explains. Flood protection should be improved to protect buildings, but at the same time it has its limits. The population and the business sector must be informed about this. “We can create some transparency on the ground about how the various players are looking at reconstruction and support communication among them,” Kuhlicke says.

Above all, the major goal of research in the disaster area is to gain scientific knowledge about reconstruction in order to be better prepared for similar events in the long term. In the future, the researchers also want to investigate this in their own Cluster of Excellence “Water Extremes”, for which they will apply in 2023. “This extensive research is necessary to understand the connections and overall complexity of extreme events and their consequences,” Merz emphasizes. “We won’t be able to prevent something like this in the future,” Bubeck says. “But we can learn how to better respond to it so that we end up with less damage and less human suffering.”

The Project

KAHR (German abbreviation for Klimaanpassung, Hochwasser, Resilienz – climate adaptation, floods, resilience) is a research consortium initiated by the Federal Ministry of Education and Research after the flood disaster in July 2021. The 13 participating institutions support the reconstruction efforts in the region and contribute scientific expertise to improving flood risk management and increasing flood resilience.
Duration: 2021 – 2024
Participating: Koblenz University of Applied Sciences, German Institute of Urban Affairs, Technical University of Kaiserslautern, Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences, Flood Competence Center, Institute of Spatial and Regional Planning, University of Stuttgart, TU Dortmund University, University of Potsdam, Institute of Hydraulic Engineering and Water Resources Management (RWTH) Aachen, District of Ahrweiler, Helmholtz Centre for Environmental Research, Eifel-Rur Water Association

The Researchers

Dr. Philip Bubeck studied politics at the University of Freiburg and environmental and resource management at the Vrije Universiteit Amsterdam. As a postdoc in the working group Geography and Disaster Risk Management, he researches the social effects of flood events, climate adaptation, and precautionary measures.
Mail: philip.bubeckuni-potsdamde

Prof. Dr. Christian Kuhlicke studied human geography, sociology, and geology in Potsdam. He is head of the Department Urban and Environmental Sociology at the Helmholz Center for Environmental Research (UFZ) in Leipzig and Professor for Sustainability and Environmental Risks at the University of Potsdam.
Mail: christian.kuhlickeufzde

Prof. Dr. Bruno Merz studied civil engineering at the University of Karlsruhe. He is head of the section Hydrology at the Helmholtz Center Potsdam German Research Center for Geosciences (GFZ) and is Professor for Engineering Hydrology and Management of Georisks at the University of Potsdam
Mail: bruno.merzgfz-potsdamde


This text appears in the university magazine Portal Wissen.