UN-backed floating city built to withstand Category 5 hurricanes is headed to South Korea

• South Korea agreed to host a UN-backed floating city prototype on Thursday.
• The project's designers envision a flood-proof city that produces its own food and water.

More than two years ago, a group of builders, engineers, and architects crowded around a table at the United Nations to discuss an ambitious concept: a floating city that could withstand natural disasters, including floods, tsunamis, and Category 5 hurricanes.

The idea wasn't entirely novel: Designers and developers have fantasized for decades about building artificial islands and metropolises on water. Even Homer envisioned a mythical floating city roughly 13 centuries ago.

But those visions were notoriously hard to advance — often because local governments wouldn't sign off on the proposals, citing concerns that there were better uses for the land.

The UN-backed project cleared that hurdle Thursday, when the city of Busan, South Korea, agreed to host a floating city in collaboration with the project's designer, OCEANIX, and the UN Human Settlement Programme (UN-Habitat). Like many coastal cities, Busan is threatened by rising sea levels.

"It just happened that Bhutan is the best place for us to deploy this prototype," Itai Madamombe, co-founder of OCEANIX, told Insider. "But this is something that we hope will be useful to all coastal cities around the world, and all coastal communities who are facing the challenge of sea level rise."

The flood-proof city could be completed by 2025

OCEANIX's floating city is essentially a collection of hexagonal platforms perched atop the water.

Hexagons are widely considered among the most efficient architectural shapes: They allow builders to conserve both space and material. Picture the orderly inside of a beehive — essentially a web of interlocked hexagons.

The city's platforms would be bolstered by a limestone coating two to three times harder than concrete, but still buoyant. The material is created by exposing underwater minerals to an electric current. In the presence of that current, it becomes stronger with time and can repair itself, allowing it to withstand harsh weather conditions.

The goal is to develop a flood-proof city that rises with the sea and produces its own food, energy, and fresh water. Cages underneath the platforms could be used to house scallops, kelp, or other forms of seafood. And aquaponic systems could use waste from fish to fertilize plants.

But the design isn't set in stone — and OCEANIX hasn't determined the size of the city yet.

Madamombe said her team will collaborate with local designers in South Korea to tailor the prototype to the local environment. OCEANIX will unveil the results of those efforts at a second UN roundtable in April, she said. From there, the team will start engineering the platforms and securing approval for construction.

The cost, subject to change depending on final design and materials, is an estimated $200 million.

"All together, it will take a total of three years," Madamombe said. "So we anticipate that by 2025, we'll see this prototype in water."

Busan is vulnerable to flooding from typhoons

Busan, a city of 3.4 million people, is home to one the world's busiest ports, so local builders and engineers have experience building along the water, Madamombe said.

The development would ultimately serve as a model for future floating cities around the world.

Both hurricanes and floods are becoming more frequent and intense as global temperatures continue to climb. A recent study from Climate Central, a nonprofit research group, found that in the worst-case scenario — 4 degrees of warming — at least 50 major cities would lose most of their populated areas over the next 200 to 2,000 years because of rising sea levels.

Coastal cities like Busan are particularly vulnerable.

Though the water surrounding Busan is mostly calm, the city has also been hard hit by typhoons in the last decade, including Typhoon Chaba, which flooded the city in 2016, and Typhoon Kong-rey, which resulted in 55,000 power outages in Busan in 2018.

Madamombe said UN-Habitat will collect data on how the Busan development fares. Her team hopes to apply those lessons to its next project: OCEANIX is in talks with at least 10 other governments about building more floating cities, Madamombe said.