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As municipalities and developers invest heavily in constructing homes in flood-prone areas, concerns about the long-term sustainability of these practices are mounting.

Developers often reap the profits, leaving future residents to face the growing risks. With rising waters due to climate change becoming an inevitability, the urgency of forward-thinking urban planning has never been clearer.

In this interview, former professor Karsten Arnbjerg-Nielsen (DMI), landscape architect Anna Aslaug Lund (Copenhagen University), and architect and urban planner Sofie Yde from Schønherr engage in a thought-provoking dialogue with Lotte C. Breengaard, Program Director at BLOXHUB. Together, they explore why embracing retreat from vulnerable areas might be key to achieving sustainable urban development amidst growing environmental uncertainty.

Lotte C. Breengaard: Why do we need to talk about retreat?

Sofie Yde: We need to discuss retreat because it is emotionally challenging, legally and economically complex, and it directly contradicts how we currently develop our cities. Moreover, it is absolutely necessary to avoid putting ourselves in unnecessarily large economic predicaments. In the future, we will be spending a significantly larger portion of the overall economy on rebuilding after natural disasters such as floods. The way we develop cities today, we are investing huge sums in areas that have a relatively short lifespan or become very expensive to keep dry. This will make us poorer as a society.

Karsten Arnbjerg-Nielsen: We are constructing houses in areas untouched by floods historically. However, we are certain, with 90% confidence, that there will be at least two floods within the next 30 years. This implies the house will need rebuilding twice before we complete paying off the mortgage. Communicating this to those who do not think in terms of probabilities is challenging

Anna Aslaug Lund: Municipalities and the state also bear responsibility toward citizens. During last October’s storm surge, I watched an interview on a TV2 program with a resident who had recently built a house in Strøby Egede, south of Køge. During the broadcast, he was seen desperately shoveling water out of his home, visibly emotional. By permitting construction in such areas, municipalities indirectly validate them as safe investments.”

Sofie Yde: Yes, what is happening right now is deeply irresponsible in many ways. We have numerous developers investing large sums in constructing homes that are subsequently sold to individuals unaware of the flood risks. Developers profit from these sales and pass the problem on to future residents.

Karsten Arnbjerg-Nielsen: In fact, municipalities have a strong incentive to improperly develop homes and buildings because the value of an area increases with new construction. This boosts tax revenue for the municipality. However, as more people move into an area, the need for dikes to protect it also grows.

Lotte C. Breengaard: What are the options for action?

Anna Aslaug Lund: Based on the UN’s climate panel IPCC’s approach to coastal zone climate adaptation, my colleagues—Associate Professor Ole Fryd, Professor Gertrud Jørgensen—and I have delineated five distinct options. “Do nothing” and see what happens, which naturally cannot be recommended. “Protection”—where Gertrud, Ole, and I focus on nature-based solutions such as green park dikes, dune landscapes, and wetlands. “Accommodate”—inviting the water in, exemplified by the Brazilian coastal town of Paraty. “Retreat”—the most radical solution, simply moving away from vulnerable areas, which is our focus today. Additionally, there’s the simplest solution: “Avoid,” which entails understanding the landscape and refraining from building in flood-prone areas. That’s what we should prioritize right now.

Karsten Arnbjerg-Nielsen: There is a large focus on dikes as a solution because they appear decisiveness. But dikes give a false sense of security because there will always be another flood. Moreover, dikes constrain our choices. Once we have invested in dikes, it becomes difficult to argue for a long-term retreat solution, leaving us with the only option of continually raising the dikes higher and higher.

Lotte C. Breengaard: How does legislation and the Natural Disaster Council support the issue of retreat?

Karsten Arnbjerg-Nielsen: They do not prevent it, but the problem is that they do not encourage it. All legislation encourages local urban densification. The Natural Disaster Council assesses whether it has been a 20-year event, and if so, they cover the damage. But when they allocate funds to a coastal stretch, the money also goes to houses that would have been flooded in a 10-year or 5-year event. Homeowners then use the money to re-establish their vulnerable homes in the same place, and we are back to square one. What the Natural Disaster Council should do is say: “On this coastal stretch, the houses would also have been flooded in a smaller event, so we do not cover the damages…” Then you start to have an economic mechanism that will motivate retreat.

Anna Aslaug Lund: The storm surges in the fall of 2023 have actually sparked a public debate about retreat as an option.

Karsten Arnbjerg-Nielsen: Yes, but retreat is something that will take decades to implement. And it also requires that you haven’t first built a large dike, because then retreat is lost. It’s about the resources. “How much do the damages cost? How much does it cost to build dikes? How much does it cost to move things? How much does it cost to avoid building more?”

The Lack of Municipal Incentives

Lotte C. Breengaard: What incentives do municipalities have to implement a retreat strategy?

Karsten Arnbjerg-Nielsen: Too often, the outcome is more housing constructed in vulnerable areas to fund a dike, rather than opting for retreat. It’s easier than telling locals, “You need to relocate because this area will become a wetland, vital for migratory birds traveling from Sweden to the Sahara.” There are specific mechanisms involved that present significant challenges

Sofie Yde: We require a comprehensive national plan that specifies the necessary land allocations and prioritizations. What must be safeguarded unconditionally? What should be relinquished gradually? Which cities should be phased out? This cannot be managed solely at the local level.

Anna Aslaug Lund: Yes, absolutely. In practice, we should be addressing multiple scales simultaneously. We must consider both the broader perspective and engage closely with citizens, integrating local conditions and narratives.

Sofie Yde: A typical Danish scenario can be found in places like Vallensbæk, where a river meets the sea along a low-lying coast. Here, numerous houses have been constructed on old salt meadows and marsh areas along the Store Vejleå River. Rainwater from the river mixes with seawater, while rising sea levels push groundwater further inland and upwards.

Another notable example is the summer house areas, crucial for the tourism industry. Many of these houses are situated at low elevations, making them vulnerable. Recently, there has been a trend towards constructing larger, more expensive, and heavier houses. Investments in sewage systems have increased due to the use of washing machines and dishwashers, and longer occupancy periods throughout the year. Summer house areas were once seen as buffers against environmental changes, but they are now increasingly considered permanent fixtures akin to urban areas.

Anna Aslaug Lund: In many areas, we’ve lost touch with the city’s relationship to the water cycle. Take Vesterbro, for example. Sønder Boulevard follows the historic coastline. About 150 years ago, what is now a densely populated neighborhood was a landscape of salt meadows where cows grazed. This history is unknown to many Copenhageners today.

Karsten Arnbjerg-Nielsen: Yes, the municipality once had a neglected area that wasn’t generating revenue. It has been transformed into an upscale neighborhood, spurring urban densification with apartments and other developments. However, it remains highly vulnerable to flooding, presenting significant challenges and costs for protection. Historically, this area was a meatpacking district for 200 years, where a flood only meant the loss of a day’s meat production. Now, with recent gentrification, a flood would bring substantial economic, social, and cultural costs. Despite all efforts, it remains inherently flood-prone.

Planning Along the Big Lines

Lotte C. Breengaard: How do we approach this in practical terms?

Sofie Yde: While we can’t predict the future with certainty, we can plan for broad trends. We anticipate a significant number of climate refugees coming to Denmark, rising water levels, and major global challenges with food production.

Karsten Arnbjerg-Nielsen: Perhaps it’s about ensuring that our decisions, no matter how short-sighted, can be easily corrected later. We’re currently making short-term decisions that shift the risk to the future. We need to think in terms of a timeline, recognizing that different areas will require strategies with various expiration dates. Over time, some areas will need to accommodate rising waters.

Sofie Yde: This can be achieved through green streets and rainwater basins, among other solutions.

Karsten Arnbjerg-Nielsen: Exactly. In some areas, local protection might be feasible for up to 200 years. In others, we might first need to accommodate the water and eventually plan for retreat after, say, 40 years. Each area requires a tailored strategy that combines ‘retreat,’ ‘protect,’ and ‘accommodate’ as needed.

Sofie Yde: That’s true for existing buildings, but when planning new neighborhoods, the first question should be, “Does it even make sense to build here?” Not “How do we build?” but “Do we build?”

Anna Aslaug Lund: We have a tendency to think we can do it all at once and think both the global and the local scale simultaneously. but that’s not effective. We need to start with a comprehensive, long-term strategy with clear milestones. Then, we can zoom in and decide, “Here, we can implement this.” For instance, a national plan might designate green corridors for certain areas where we should ‘retreat,’ ‘protect,’ or ‘accommodate.’

Sofie Yde: The ‘Vision 2100’ plan developed for Copenhagen was quite a good initiative. It made clear decisions about where densification and development should occur and where it should not. Amager Fælled, for instance, was designated as a nature area and retreat zone. However, a change in government later opted to develop it, highlighting the difficulty of maintaining long-term strategies in a volatile political environment. This underscores the need for legally binding plans that are resistant to frequent changes.

Karsten Arnbjerg-Nielsen: Legislation must ensure continuity and commitment to these strategies. Without such legal frameworks, achieving the long-term adaptation necessary for climate resilience is nearly impossible.

Sofie Yde: Public awareness and engagement are also crucial. Citizens need to understand the reasoning behind certain decisions and the importance of adapting to climate realities. This requires transparent communication and education about the associated risks and strategies.

Anna Aslaug Lund: It’s a cultural shift. We need to change our mindset from fighting nature to coexisting with it. This fundamental change demands time, education, and collective effort.

Lotte C. Breengaard: Thank you all for the insightful discussion. It’s clear that while retreat is a challenging and complex issue, it is a critical strategy for achieving sustainable and resilient urban development in the face of climate change.


This interview was originally published in the Danish periodical Landskab (105) in February 2024.