Can extreme flooding be prevented?

Dangerous flooding has killed more than 40 people in northeast China, as torrential rains caused by typhoon Doksuri hit the capital Beijing and the surrounding area. In Slovenia in Central Europe, two-thirds of the country is battling flooding, landslides and a dam breach caused by heavy rain. Meanwhile, severe weather also hit Austria, Poland, Croatia and Slovakia.  

They're not the only countries to be slammed by deadly storms this summer. At the beginning of July, the US, India, Britain and Spain saw unprecedented rainfall trigger flash flooding that claimed lives and damaged infrastructure. 

"Warmer air can carry more water vapor. Record heat brings record rains brings record floods," tweeted Eric Holthaus, a US-based meteorologist and climate journalist, when the "unbelievably scary" flash floods occured in Spain.  

 

Strategies for climate adaptation

With record floods in countries from Germany to Pakistan and beyond linked to a worsening climate crisis in recent years, how can communities better adapt to limit the damage?

Speaking to DW following the 2021 flooding that claimed at least 200 lives in western Europe, Lamia Messari-Becker, a civil engineering professor focused on sustainable building and design at Germany's University of Siegen, said in adapting buildings to withstand floodwaters, it is worth looking at earthquake-resistant architecture.

In such buildings, the depth of the foundation, structural design and construction materials are specifically chosen to be able to handle extreme flooding. 

"We need to reinforce basements so that they can also fill up with water and people can quickly get to safety," Messari-Becker said. "It's also about the reinforcing measures needed for outer walls, for roofs."

Other measures highlighted by experts include retention valves on sewage connections, which prevent floodwaters from backing up into homes, and waterproofing windows and doors on the lower levels of buildings.

"Our damage evaluations show that private precautionary measures can significantly reduce flood damage," Annegret Thieken, a professor who focuses on natural hazards research at the University of Potsdam told DW in light of the 2021 floods. She also pointed out the need to secure potentially destructive elements like fuel tanks used to heat homes.

"Fuel oil can penetrate deep into the masonry and also damage neighboring buildings," she said. "In severe cases, oil damage can make buildings uninhabitable. Flood proofing can prevent oil tanks from heaving up, reducing damage to buildings and the natural environment."

Weatherproofing cities: Sustainable approaches to flood management

It's not enough to just focus on buildings. Cities and other urban areas need to think about controlling the water before it has a chance to flood basements in the first place, by reinforcing reservoirs and dams that can help absorb sudden surges.

Flooding such as that in the devastated Ahr region south of the German city of Bonn in 2021 show that small streams in narrow valleys, where the water doesn't have much room to spread out, can turn into deadly torrents within hours. In such places, Messari-Becker said dams and dikes need to be raised and expanded to better protect cities from high water levels.

But that is not cheap. Simply extending a dike, for example, can cost at least €1 million ($1.2 million) per kilometer. And the narrower a valley is, the more costly such measures become.

Boris Lehmann, a professor of hydraulic engineering at Germany's Technical University of Darmstadt said, "in order to effectively protect infrastructure against such extreme events, the current design of our water management and hydraulic engineering systems are not sufficient — as the current dire consequences have shown." 

Experts have stressed the urgency of future-proofing aging infrastructure over the next decade, but in the aftermath of the 2021 flooding in Germany and Belgium, Lehmann said we can't expect better building measures to solve all our problems.

"From a technical, economic and practical point of view, it's not possible to completely reassess, reconstruct and thus protect all elements of our built environment and infrastructure due to such extreme weather events." 

Nature-based solutions for flood prevention

That's where planners and engineers will have to find ways to work with the natural world, rather than trying to control it. Wherever possible waterways should be allowed to flow as nature intended, and not be altered or straightened. Doing so concentrates and further accelerates the volumes of water during a flood event.

Rather than confining rivers, levees should be moved back to make space for flood plains — wide open green spaces that can serve as overflow reservoirs during floods. Such spaces were expanded along the Elbe River in eastern Germany, following several destructive flooding events in the early 2000s.

Another approach is to make urban areas more permeable, so that water is more easily absorbed over a wider area and not concentrated in specific spots. 

The German town of Leichlingen, southeast of Düsseldorf, has been hit by severe flooding several times in recent years. To ease the stress on their water management, they have been experimenting with a new planning model known as a "sponge city." 

The idea is to channel rainwater from roofs, squares and streets into grass-covered ditches at the side of the road. Excess water would then be allowed to drain away naturally and add to the local groundwater, reducing the load on water management infrastructure. Backup cisterns would also be installed to collect overflow and could be used to water the city's green spaces.

The sponge city concept comes from China, where a number of cities like Qian'an and Xingtai in the north of the country, are experimenting with the idea. Still, in spite of the sponge infrastructure, intense rainfall triggered flash flooding in Xingtai, killing five people, reported local media last week. 

While China's sponge city strategy is "very ambitious," it wasn't designed to withstand extreme storms like Doksuri, Hongzhang Xu, who specializes in urban planning and infrastructure development at the Australian National University in Canberra, told environmental journal Nature. It needs to be updated to reflect heavier rainfall and should be implemented in tandem with other approaches like improved drainage systems that  "divert the water away as soon as possible," he added.

Emergency preparedness: empowering communities

Improving infrastructure and water management systems won't help if people don't know how to react when faced with a wall of water. Which is why Lehmann, the hydraulic engineering expert at the Technical University of Darmstadt, stressed the need for an increased public awareness.

"Especially in the case of flash floods caused by extreme weather, there's not just a lot of water — there's also a great deal of floating debris, garbage and other things moving with the water," he said, adding that people who go into these waters risk drowning and being crushed.

He said ongoing education campaigns were necessary to teach the public how to react in extreme situations — for example, how to escape from a car caught up in a current.

"'Run away from the water and get to safety as quickly as possible — we should start teaching such rules of conduct as early as elementary school," he said. "In the case of emergency, it can save lives."

This article was first published on July 10, 2023, and updated with information on recent floods in Slovenia, China and elsewhere on August 7, 2023