Should Europe Build Walls, Move Inland, or Learn to Live With Floods?

Scientists in Europe have completed a large study on how coastal communities should prepare for rising seas. The research looked at more than 41,000 coastal areas across Europe and ran calculations all the way to the year 2150. Researchers wanted to find the smartest and least costly way for each area to handle flooding from the ocean. Their findings suggest that simply building bigger walls along the shore is not always the best answer.

The study looked at three main choices that communities have when dealing with coastal flooding. The first choice is protection, which means building hard barriers like dikes — thick walls that hold back seawater. The second choice is accommodation, which means making buildings stronger and more flood-resistant so people can stay even if water gets in. The third choice is retreat, which means moving people and buildings away from the most dangerous low-lying areas near the coast.

Researchers found that nearly one in four stretches of European coastline would be better off choosing retreat rather than protection. That means instead of spending money on bigger and bigger sea walls, it could actually cost less in the long run to help people move to safer ground. Right now, most European countries focus on building protective barriers, but this study says that approach needs to change. Scientists believe both accommodation and retreat should be built into official government plans for the future.

Sea levels are rising because of climate change, and they are expected to keep rising for many decades. Warmer temperatures cause ocean water to expand and glaciers to melt, adding more water to the sea. Some parts of Europe's coast are also slowly sinking into the ground, which makes flooding an even bigger problem. Researchers used data from the United Nations climate science group, known as the IPCC, to model what sea levels might look like under different pollution scenarios.

The research team used computer models to figure out the costs of each option in every coastal area. Building a dike costs millions of euros per kilometer, and keeping it in good shape costs about one percent of the original price every year. Helping someone move away from the coast was estimated to cost about six times the average income per person in that area. Making buildings flood-proof cost roughly $8,600 per person for every meter of flood-proofing work done.

The scientists ran the numbers using a method called multi-stage cost-benefit optimization. This is a fancy way of saying they compared costs and benefits at many different points in time, not just right now. They wanted to find the path that would save the most money while also protecting the most people. The math was done separately for each of the more than 41,000 coastal zones in the study.

Hotspot areas with extra-fast sinking land, like parts of northern Italy, the Netherlands, and near the city of Thessaloniki in Greece, face even faster rising water levels. In some of these places, the water is effectively rising by up to four millimeters more per year than the ocean average. That may sound small, but over many decades it adds up to a serious difference. These regions may need to act sooner and more boldly than other parts of Europe.

Experts hope that governments and city planners will use this research to build smarter, more flexible plans. Protecting every inch of coastline with walls may be too expensive and not even possible in the long run. In some places, helping communities adapt by building stronger homes or moving to higher ground could save lives and money. The study is a call for Europe to think bigger — and plan further into the future — when it comes to the rising sea.