Imagine stepping into a city where sustainability isn’t just built upwards but also downwards. While cities worldwide grapple with intensifying climate risks—flooding, heatwaves and infrastructure strain—an untapped solution lies right beneath our feet. The underground isn’t just for subways and parking garages; it holds immense potential for climate resilience, urban sustainability and even equitable development.

A Hidden Asset for Climate Resilience

Underground spaces can serve multiple functions in cities across the world—beyond storm shelters and transport hubs. They offer natural insulation, reducing energy demands for heating and cooling. By moving utilities and industrial functions underground, cities can reclaim valuable surface land for green spaces, affordable housing and pedestrian-friendly design. This dual benefit of climate adaptation and urban livability is a win-win.

Cities worldwide are already pioneering underground solutions. Take Montreal’s greenhouses, which harness geothermal stability to grow fresh produce year-round, insulating crops from extreme weather. In the Netherlands, underground transit hubs are designed to be flood-resilient, meaning they incorporate waterproof barriers, elevated entry points and advanced drainage systems to prevent inundation from rising waters while ensuring uninterrupted connectivity. Singapore’s Deep Tunnel Sewerage System (DTSS) is another example of smart underground infrastructure. This massive, gravity-driven network of deep tunnels eliminates the need for multiple conventional treatment plants, freeing up valuable land in the densely populated city. By channeling wastewater efficiently to centralized treatment facilities, the DTSS reduces energy demand, lowers operational costs and enhances Singapore’s long-term water sustainability.

Despite these successes, U.S. cities have been slow to adopt underground solutions at scale. But there are glimmers of progress. New York City has already demonstrated the potential of underground spaces with its ambitious projects. The Oculus at the World Trade Center is not just a transit hub—it’s a striking architectural landmark that houses a bustling shopping center, cultural events and public gathering space, all while being engineered to manage stormwater surges and extreme weather. The revitalization of Hudson Yards has transformed once-overlooked rail yards into a dynamic mixed-use district, featuring underground infrastructure that supports efficient transit connections and climate resilience. Meanwhile, Penn Station’s redevelopment integrates modernized subterranean corridors, improved flood mitigation and expanded transit capacity, making daily commutes smoother while future-proofing the city’s core. These projects showcase how the use of underground space can be a key component of larger climate adaptation strategies, balancing resilience with functionality and urban vitality. 

Beyond Bunkers: The Future of Urban Development

Helsinki provides a masterclass in subterranean urbanism. The city’s underground master plan incorporates shopping centers, data centers and even a subterranean swimming complex—all designed to function efficiently while reducing land-use strain. Similarly, Hong Kong’s rock caverns house reservoirs and waste treatment facilities, freeing up above-ground space for community use.

Meanwhile, Paris is planning to optimize its underground infrastructure to include pedestrian tunnels that connect key transit hubs and art exhibits, while Tokyo has built underground flood reservoirs that prevent urban flooding during typhoon season. These examples highlight how underground development is not just feasible but essential for future-ready cities.

The Potential of Subterranean Urbanism in the U.S.

Despite clear benefits, U.S. cities face hurdles in adopting underground solutions for climate resilience. High construction costs, complex geological conditions and bureaucratic inertia slow progress. However, cities can learn from international models and take immediate action:

• Policy reforms: Update zoning laws to encourage underground development, as seen in Singapore and Helsinki. In the U.S., cities need more incentives to incorporate underground climate resilience strategies into urban planning.
• Public-private partnerships: Encourage investment in subterranean infrastructure through tax credits, grants and long-term planning frameworks. New York’s Hudson Yards leveraged private funding to build sustainable underground infrastructure—this model can be expanded.
• Technological innovations: Advances in tunnel boring, geothermal integration and smart monitoring can reduce costs and enhance feasibility. Companies like Herrenknecht, a global leader in tunnel boring machines, and Robbins, known for their innovative tunnel excavation equipment, are driving progress in making underground infrastructure more efficient. These companies have been involved in large-scale projects worldwide, such as high-speed rail tunnels and underground energy storage systems, demonstrating how advanced tunneling technologies can lower construction costs and improve the viability of underground solutions.

Moreover, cities should prioritize pilot projects that showcase the benefits of underground urbanism.  For instance, Los Angeles could expand its underground stormwater capture systems—like the Tujunga Spreading Grounds—to enhance water resilience. Located in the San Fernando Valley, the Tujunga Spreading Grounds is a large-scale stormwater management project designed to capture and recharge groundwater. Originally built in the 1930s and recently upgraded, it now diverts millions of gallons of stormwater from the Los Angeles River into underground aquifers, helping to reduce reliance on imported water.

Expanding such infrastructure beneath urban areas could be a game-changer for drought-prone cities. Underground reservoirs, designed to capture and store excess stormwater, could provide a sustainable water source while preventing flooding during extreme weather events. Cities like Phoenix or Houston, which face both water scarcity and seasonal flooding, could adopt similar underground systems—integrating them with parks and public spaces to create dual-purpose, climate-resilient urban areas. By leveraging subterranean solutions, U.S. cities can build more adaptive and sustainable water management systems without sacrificing valuable surface land.

A Call to Action

To truly future-proof U.S. cities, we must rethink urban space—above and below ground. By integrating underground spaces into climate resilience strategies, cities can create cooler, greener and more adaptable environments. The shift requires political will, investment and public engagement.

The future of cities may not be sky-high, but instead, deeply rooted—underground. It’s time to dig into this opportunity, not just as a futuristic concept but as an urgent necessity for a climate-resilient future. Cities that embrace this vision will be better positioned to thrive in the face of climate change, urban density pressures and shifting sustainability demands.

Mahak Agrawal is Board Member for the International Tunnelling & Underground Space Association’s Committee on Underground Space (ITACUS) and the Founder of All Bits Count (ABC) initiative.