After flash floods, Germany aims to build back sustainably

Experts say there needs to be a fundamental change in how we build in areas at risk of floods.

The Ahr River broke its banks on July 14, flooding thousands of properties in the valley.

Alfred Sebastian surveys the space that used to be his kitchen. There's no floor, the walls are stripped bare, and the only appliances to be seen are hardware tools and structural drying machines. This is what's left after the catastrophic floods that swept through Dernau, his village in the Ahr Valley, western Germany, in mid-July. "It all happened so quickly that there was no way to get any of your belongings to safety. We weren't expecting this amount of water," he says.

Known for its picturesque vineyards, the region was left devastated after heavy rainfall turned the usually peaceful Ahr River into a raging torrent. Sebastian, who is Dernau's mayor, was forced to retreat to his home's upper floors as the water inundated the basement and the ground level. However, since his house was a bit further up the hill, he was better off than most.

More than 130 people in the valley died and 17,000 others are grappling with damaged homes or lost belongings. In Dernau itself, 400 of the town's 500 houses are now uninhabitable, according to Sebastian. These residents are now facing questions such as whether to relocate, or whether to stay and live with the potential flood risk. "There are people who have already sold their house because they can't cope with the sound of rain," Sebastian says. "They don't want to live with the constant fear that this flash flood could happen again. I myself can deal with it, but I must admit it is always in the back of my mind." 

Rebuilding in a floodplain

The government has approved a €30 billion ($34 billion) fund to support those affected by the flood. Authorities have also published updated flood zone maps of the Ahr River Valley, showing where new construction is no longer permitted. Of the thousands of homes that were damaged, local authorities have said just 34 are not allowed to be rebuilt due to flood risk.

Most residents in the floodplain will be allowed to renovate and rebuild their homes as before, in the same spot. But there will be restrictions for those building from scratch. The details are still sketchy in the wake of the flood, but the regulating authority says this could include measures such as installing fuse boxes on the upper floors so that power supply won't be interrupted by a flooded basement. It's also not yet clear whether insurers will provide natural hazard coverage for residents rebuilding in a designated floodplain, says Sebastian.

Live with risk or relocate?

Professor Christian Kuhlicke, an expert on environmental risks and extreme events at Leipzig's Helmholtz Center for Environmental Research, says there needs to be "a fundamental change" in the way people build in small river catchments like the Ahr Valley, where homes are often unprotected from flood risk. "Otherwise it becomes very costly and potentially also very deadly."

Kuhlicke says the right decision for some property owners in the region might be to move to higher ground. He cites the U.S. town of Valmeyer, which relocated entirely out of the Mississippi Valley up into the nearby hills after a devastating flood in 1993. "Now it's a prospering community close to the borders of St. Louis," he says. "So if people are really convinced that moving out of the floodplain is a smart decision, these people should be supported."

In the case of the Ahr Valley, he would like to see more regulation, including incentives for flood-resilient buildings. Instead, he says decisions about how to rebuild, or whether to relocate, are largely left up to the residents and communities themselves: "That means that the political signal is rather: We want to keep the communities in the valley."

Floodproofing homes

Kuhlicke stresses that while there was nothing that could have prevented the July flash floods because the volume of rainfall was just too great, there are ways people can adapt their homes to limit damage. For example, by dry floodproofing homes — reinforcing doors, windows, and other openings to prevent water entering the building. Or wet floodproofing — allowing the water to enter the building in the event of a flood and using water-friendly building materials that won't get water-logged and destroyed.

Rebuilt homes should also be "designed in a way that's not impacting climate change negatively by contributing CO2 emissions," he says. "One can only hope that they have really some good engineers there and architects that help people to rebuild in a way that is more resilient and more sustainable." But it’s not only the houses that need to change. Sebastian says it will also be crucial to implement measures to keep more water in the landscape in future, including building retention basins upstream and in side valleys, to reduce the impact of any future flooding.

A chance to rebuild differently

Sebastian also sees the town's reconstruction as an opportunity for change. A group of researchers has put forward a proposal for how the region can generate 100 per cent of its energy supply from renewables by 2027, for example, by using wind power and installing solar panels directly onto roofs being repaired.

He says one of the main lessons drawn from the flood is that homes in Dernau won't be fitted with fossil oil heating in future — currently used by about a quarter of homes in Germany. Many oil heating systems leaked in the flood, effectively contaminating houses and upping the overall damage and cost. Instead, Sebastian wants to build a modern village heating network powered by renewable energy. "But this requires state support," he says. "If the Ahr Valley is to become a model region with a sustainable energy infrastructure, we're going to need more funding, and fast, otherwise people here will simply get their own fossil fuel heating systems back again."

Building resilient homes — is there a trade-off?

Climate change is expected to make extreme weather events more powerful and more frequent across the globe in the future. Building resilient homes will clearly be important, as will switching to more sustainable forms of energy. But what about the materials used in the reconstruction process? The construction sector, including the manufacture of building materials such as concrete and steel, accounted for almost 40 per cent of global energy-related emissions in 2019.

"There is absolutely a trade-off, and there is a choice to be made about construction materials," says Elizabeth Hausler, the CEO of Build Change, an NGO that builds disaster-resistant houses for people who face risks from hurricanes, floods and earthquakes. "In hurricane-prone areas, for example, there is a strong preference toward heavy, sturdy concrete blocks," she adds. Concrete is seen as a reliable, climate-resilient material, but the cement used to produce it is responsible for 8 per cent of global CO2 emissions alone. Hausler stresses the main priority should be preventing houses being lost in the first place, "so that we don't have an increased carbon footprint from rebuilding."

In the village of Dernau, the streets are largely empty. A brown water line is still visible on the upper levels of many buildings, showing just how high the river came. Still, Mayor Alfred Sebastian says he expects 90 per cent of the town's 2,000 residents to return and rebuild their homes — a process that will likely take years to complete. "This used to be a paradise," he says. "And now after the flood it's more like a desert. I hope that in 10 years' time we will be back better than ever and that we never have such a catastrophic flood again. But, of course, nobody can guarantee that."