Written by Luisa Antunes with Tobias Hoffmann and Laia Delgado Callico.
Since ancient times, from the Roman Empire around the Mediterranean Sea to floating islands used by the Uro people of Peru, civilisations have settled near water.
Today, rising sea levels place coastal cities under constant threat. An estimated 250 million people currently live on land below projected annual flood levels, often in coastal cities such as London, Lagos, Mumbai or Shanghai; and this number may rise to 630 million by the end of the century. An additional 318 million people have been displaced since 2018, due to climate disasters.
Many of these cities have already taken measures to adapt to rising sea levels. Shanghai is protected by a gigantic protection system, while New York City has created a system to shield its island-located economic borough of Manhattan. The government in Indonesia took one of the most drastic actions, deciding to move its entire capital inland, mainly because it was sinking and experienced regular flooding. The location of the new capital, Nusantara, has been criticised for leading to the displacement of indigenous populations and the destruction of vast areas of natural rain forest, essential to counteracting climate change.
Could it be that, instead of humankind fleeing from water, building on it could serve as a better long-term solution? What would the creation of entire water cities entail for societies, economies and the environment? What if populations could live on water instead of facing displacement and migration? The combined effects of climate change, land subsidence and accelerated urbanisation could force us to rethink the use of water surfaces on Earth as potential settlement areas, as an alternative to an Earth surface made uninhabitable by over-population and climate catastrophes.
Potential impacts and developments
Despite a popular image of modernity, the concept of living on water is not new. Overwater structures have been designed, built and used for centuries worldwide. Amsterdam is a present example of a city experimenting with totally floating houses. These are built as small modules, with individual buildings connected by plug-in systems, whose weight is balanced by concrete fundaments lying underwater. Energy, fresh water and internet connections are all provided via a land plug-in.
City planners believe that entire floating districts could both improve the housing crisis that afflicts many coastal cities, such as Amsterdam or Barcelona, and contribute to attenuating flooding crises. A floating system would allow constructions to adapt to waves, tides and even storms, including hurricanes. The flexible plug-in and out system of floating cities would also allow for new ways of city planning: sports stadiums, schools and parks could be easily moved to adapt to new demand. In addition, these flexible modern city models could serve as attractive tourist destinations.
The first overwater cities are expected to be located close to the coast. Such projects would be designed with climate adaptability in mind, while still offering contact with the mainland. Since plug-in systems have water and energy capacity limitations, self-sufficiency through solar power and water heat pumps would be essential.
As heat waves increase in frequency and severity, the surrounding water could be used to cool buildings. Sustainable public infrastructure and transportation strategies will also need to be reimagined. Several current coastal megacities are characterised by an uncontrolled, heterogeneous growth, which leads to high-cost constructions that produce huge amounts of waste. Ocean plastic is already a major issue for the marine ecosystem and tourism, so waste removal will need to be well organised. Cities on water will require a highly functional public sector. An additional risk is the cost itself: if living on water continues to be too expensive for the vast majority of the population, these cities might fall short on providing part of the solution to climate change-caused displacement and migration.
If cities continue to grow on water, additional protection from heavy storms will be necessary, resulting in disturbance of the surrounding marine structures, as this will affect currents and rivers, and inevitably change ecosystems. The ecological equilibrium will be disturbed, as underwater building foundations will create new habitats for micro- and macro-organisms, including pests. While underwater reef structures might pose opportunities for aquaculture and food production, constant maintenance will be required.
Keeping water out of liveable spaces is also not easy. A substantial concern linked to floating constructions is to constantly clean and renew surfaces with material free from leaking pollutants, anticipating how little we know about marine ecosystems. A completely floating city without direct land-based production will force us to find ways to autonomously produce fresh water and energy.
Although cities on water could serve as an answer to climate change, and the associated technology is potentially sustainable, their climate impact might still be immense. To stabilise underwater buildings, huge amounts of concrete are currently used, as concrete displaces water very effectively. However, concrete production contributes to 8 % of global CO2 emissions today, and concrete production has created an international competition for sand, the market for which is currently reaching record prices.
Economic considerations are just one aspect of the huge impact cities on water could have on international relations. Another might be their existence alone: cities on water would change international sea borders as they are currently legally defined. Countries might be tempted to use their floating cities to create additional territories. The growing value of marine territory could intensify, and we are already witnessing the effects of growing global tensions over disputed territorial areas. There is a risk that cities could also establish themselves as extraterritorial city-states outside national legislation and develop as tax havens.
The European Union has a history of structuring urban planning, and existing regional urban development plans already address many aspects pertaining to cities on water, such as those on the circular economy, energy transition, housing and sustainable land use. Many outlined requirements, such as the efficient use of solar and waterpower systems, effective energy storage systems and zero pollution policies, are also part of the European Commission’s sustainability goals, namely in the European Green Deal. Furthermore, the European Bauhaus aims to foster sustainable living spaces whilst anticipating future living needs.
Many ‘smart cities’ are located at the coast and, therefore, potentially future cities on water. Anticipatory policy-making could start by integrating current ‘smart-city’-related policies in the projection of future-oriented living models, as well as assessing global needs and fostering international cooperation on worldwide issues. The Netherlands currently take a leading role, with decades-long experience in dealing with challenges posed by cities on and by water.
Legislation will also need to address fundamental housing issues, such as mortgage and financial classification laws. Clear legislation will be instrumental to ensuring future equal access to living spaces on water. The legal status of floating cities is a difficult challenge that requires revisiting long-established international agreements. Who owns cities on water might be one of the most relevant questions in the 21st century. Through its marine science expertise, strategically relevant industries and diplomatic relationships, the EU currently takes a leading international role. As it shares its marine environment, trade, security challenges and opportunities with global partners, the long-term success of the EU’s ocean governance will depend largely upon global action and collaboration.
Read this ‘at a glance’ on ‘What if we built cities on water?‘ in the Think Tank pages of the European Parliament.
Listen to policy podcast ‘What if we built cities on water?’ on YouTube.