As climate change accelerates, space becomes scarcer, and sea levels continue to rise, cities can no longer be designed as they once were. Far from the utopias of the past, tomorrow’s urban spaces must be resilient, flexible, and deeply connected to their natural environments. This evolution is not a passing trend—it’s a vital necessity. Inspired by the book The Future of Cities: Underground or Floating? by Léwis Verdun, this article explores the foundations of sustainable urbanism and strategies for designing cities that can withstand the environmental shocks to come.

Sustainable urbanism: a necessary response to 21st-century challenges

Rapid urbanization has led to the unchecked expansion of megacities, many of which are poorly equipped to deal with climate crises. Today, urban resilience is the watchword: building alone is no longer enough—we must anticipate, adapt, and protect.

Urban heat islands, intensified by concrete and asphalt, create stifling microclimates. At the same time, rising sea levels threaten entire coastal cities. Without a decisive shift toward sustainable urbanism, these phenomena will only worsen, endangering the health, safety, and quality of life for millions.

Sustainable urbanism goes far beyond planting a few trees or reducing energy use. It calls for a deep transformation in how we design cities—integrating nature, flexible space usage, and proactive risk management. This includes radical solutions like building underground or on water.

Underground or floating: two visions for climate-adapted cities

Léwis Verdun’s book explores two concrete—though sometimes perceived as extreme—solutions: underground cities and floating settlements. These models are not science fiction but real-world projects at varying stages of development.

Underground cities, like those developed in Helsinki, take advantage of the thermal stability of the Earth, offer natural protection from extreme weather, and free up surface space for green areas, pedestrians, or urban agriculture. However, they come with significant challenges: ventilation, lighting, the psychological impact of confined spaces, and excavation costs.

On the other hand, floating cities such as OCEANIX Busan—backed by the UN—envision fluid, modular urbanization that can adapt to changing sea levels. These floating platforms could house thousands of people while remaining energy- and food-autonomous. Yet, they too face obstacles: structural stability, anchoring systems, freshwater access, waste management, and social integration.

These two models address different issues but share a common goal: adapting cities to their environment rather than attempting to dominate it.

Nature-inspired design: biomimicry and adaptive architecture

As traditional infrastructure reaches its limits, a powerful movement is gaining ground: biomimicry. This design approach draws inspiration from living organisms to create more resilient structures. For example, some cities are exploring naturally ventilated buildings modeled after termite mounds or water-absorbing surfaces that mimic forest floors.

In floating urbanism, architects study coral reefs and mangroves for their wave-dissipating and soil-stabilizing properties. For underground cities, root systems can inspire the design of ventilation, movement, and water supply networks.

This adaptive design approach also embraces smart technologies: climate sensors, automated energy systems, and modular space layouts. The aim is to create living cities that can self-regulate and evolve with their environment.

Practical guide: preparing cities for the climate of tomorrow

Here are concrete strategies to reimagine cities through the lens of environmental adaptation:

Sustainable urban adaptation strategies

  • Promote vertical urbanism to free up surface space

  • Integrate controlled flood zones and green buffer areas

  • Multiply green roofs and active façades

  • Reclaim industrial wastelands and reconnect them to green networks

  • Develop multimodal transit hubs to reduce car dependency

  • Use biosourced and local materials in construction

Examples of pioneering cities

  • Singapore: large-scale integration of green infrastructure

  • Kuala Lumpur: SMART tunnel combining transportation and emergency drainage

  • Rotterdam: experimental floating district in Schoonschip

  • Copenhagen: “sponge city” model to absorb rainwater

Tools for urban planners and policymakers

  • GIS (Geographic Information Systems): map risk zones

  • Life Cycle Assessment (LCA): evaluate the environmental impact of materials

  • Flexible zoning: design multipurpose, adaptive spaces

Far from being a purely technical debate, the question posed in The Future of Cities: Underground or Floating? is a civilizational issue. Our urban planning choices today will shape the world we leave to future generations. Whether digging into the Earth or floating on water, we must approach these challenges with creativity, pragmatism, and a sense of responsibility.

Léwis Verdun’s book does not choose between the two paths but instead proposes a hybrid, context-sensitive approach. Some regions will leverage underground potential, while others will embrace the marine frontier. What matters most is opening up our imagination, learning from existing innovations, and understanding that the future of cities depends on their ability to coexist with the planet.

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