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Climate change and land-use changes increase likelihood of flood events

Climate change and land use changes increase the risk of flooding

A year has passed since the flood disaster in the Eifel, in which the flood damaged or destroyed more than 100 bridges. Credit: Dominik Kuhn

The German government estimates the total losses from the catastrophic floods in July 2021 at 32 billion euros. In two studies, one of which is currently available in Natural Hazards and Earth System Sciences, researchers at the Karlsruhe Institute of Technology (KIT) have investigated how precipitation, evaporation processes, water flow and runoff led to this flooding. To improve future preparedness for such extreme events, they recommend that risk assessments take more account of the landscape and river courses, how they change and how sediments are transported. In addition, projections show an increase in the spatial magnitude and frequency of such extreme events, as well as greater amounts of precipitation.

The July 2021 flood was one of the five worst and costliest natural disasters in Europe in the past 50 years. More than 180 people were killed and more than 10,000 buildings were damaged. Critical infrastructure, such as power grids, water mains, bridges, railways and roads, was partially or completely destroyed. The total magnitude of the floods in the Eifel on 14 and 15 July 2021 even surprised the experts. A combination of several factors contributed to this disaster. “We investigated how precipitation, evaporation processes, water flow and runoff led to this flooding,” said Dr. Susanna Mohr, General Manager of the Center for Disaster Management and Risk Reduction Technology (CEDIM) at KIT, who led the interdisciplinary team from several KIT institutes that compiled the study.

Debris magnifies both the magnitude and impact of the Ahr flood

The estimated amount of water flowing through the Ahr River in the 2021 floods was comparable to that of the historic floods of 1804 and 1910, but measured water levels were significantly higher in several places in 2021. “We saw that the type of debris – the material transported by the flowing water – changed significantly. Along with eroded sediment and existing dead wood, anthropogenic materials — which are man-made — played a critical role,” says Mohr.

“For example, cars and trucks, trailers, dumpsters and construction materials piled up around bridges, creating additional bottlenecks and exacerbating the effects of the flooding.” To improve future preparedness for such extreme events, Mohr advises that flood risk management considers the landscape, infrastructure and buildings, along with river courses and their changes and possible sediment transport, when conducting hazard assessments.

Amount of precipitation not unprecedented

The researchers also compared the July 2021 precipitation event with historical precipitation records. “Our analyzes show that the observed total precipitation was one of the highest in Germany in the last 70 years, so it was extreme but not unprecedented,” said Dr. Florian Ehmele of KIT’s Institute of Meteorology and Climate Research-Department Troposphere Research (IMK-TRO).

“The precipitation events that led to the major floods in Berlin and Brandenburg in 1978 or on the River Elbe in 2002 were much stronger in terms of both intensity and magnitude or duration.” However, according to Ehmele, previous precipitation events similar to those of July 2021 were mainly observed in eastern and southern Germany and less frequently in the west.

Simulations show that climate change amplifies future floods

The KIT researchers also simulated the flooding under different climate conditions. “The intensity of such precipitation events increases by about seven percent with each degree of warming. The simulations show that the amount of precipitation is already eleven percent higher than under pre-industrial conditions,” says Dr. Patrick Ludwig, head of regional climate. modeling working group at IMK-TRO. “So we should expect a further increase in precipitation as global warming continues.”

But Ludwig warns that this won’t be the only future problem. “Our projections show that such extreme events will cover larger areas, last longer and become more frequent,” he says.

The public needs better risk awareness

The severe floods of July 2021 showed the importance of being prepared for such events and responding appropriately, the researchers said. In order to improve resilience in the event of disasters, which would reduce damage and the number of victims, they argue that social aspects and the vulnerability of infrastructure should also be taken into account in addition to the potential dangers. An essential part of resilience is public risk awareness, ie knowledge of rapid and appropriate possible responses in the event of a disaster.

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More information:
Susanna Mohr et al, A multidisciplinary analysis of the exceptional July 2021 flood in Central Europe. Part 1: description and analysis of the event, Natural Hazards and Earth System Sciences (2022). DOI: 10.5194/nhess-2022-137

Provided by Karlsruhe Institute of Technology

Quote: Climate change and land use change increase the likelihood of flooding (2022, July 21) retrieved July 21, 2022 from https://phys.org/news/2022-07-climate-land-use-likelihood-events.html

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