Climate AdaptationUnderground Space: The Lesser-Known Champion of Climate Resilience

Underground Space: The Lesser-Known Champion of Climate Resilience

Mahak Agrawal
Mahak Agrawalhttps://www.linkedin.com/company/all-bits-count/
Mahak Agrawal is an urban planner, climate science and sustainability expert, global thought leader and LinkedIn Top (Green) Voice, and former United Nations fellow. In 2024, Mahak was nominated by the Government of India as a climate scientist and urban sustainability expert to the Intergovernmental Panel on Climate Change (IPCC). As a Shardashish Scholar and Environmental Fellow at Columbia University’s School of International and Public Affairs, Mahak earned her second master’s in public administration with a specialisation in environmental science and policy. As an Environmental Fellow at Columbia University, Mahak led the research project examining the future of food systems through its demand-supply chains. She earned her first master’s degree in urban planning from the School of Planning and Architecture Delhi, India. She is a recognized expert in the fields of climate policy, ESG reporting and corporate carbon management, urban sustainability, and social impact. Recognized for her achievements in accelerating the Sustainable Development Goals in India through public health initiatives, Mahak was nominated for the Gates Foundation’s 2021 Goalkeepers Global Goals Award. In various capacities, she has worked with the Organisation for Economic Co-operation and Development (OECD); the Ministry of Home Affairs and the Ministry of Housing and Urban Affairs, the Government of India, the UN Environment Programme (UNEP), the World Bank Group, European Climate Foundation, and the Institute of Transport Economics, Oslo. Mahak has served twice as an expert reviewer for the United Nations Intergovernmental Panel on Climate Change (IPCC), authored numerous scientific publications, and presented her works globally, including at the United Nations. She is a Steering Board Member of the ITA Committee on Underground Spaces (ITACUS) and a TEDx fellow. In 2023, ITACUS nominated Mahak to represent the organisation at the World Food Forum. She also experiments with her mum to create sustainable art advocating for climate action and a sustainable future.

This article was written for CityChangers.org by Mahak Agrawal, Steering Board Member of ITACUS and Founder of All Bits Count (ABC). In it, she explores how cities around the world are looking, and ought to look, beneath our feet for answers. Critically, she reminds us, while digging down may reinforce climate adaptation, it also frees up space above ground for more enjoyable purposes.

Cities are feeling the pressure of climate change—floods, heatwaves, and overcrowding are threatening their survival. Urban areas are home to more than half of the global population, and this density amplifies climate risk because concentrated populations strain infrastructure, increase demand for resources like water and energy, and create heat islands, making cities more vulnerable to extreme events. For instance, during Hurricane Sandy in 2012, New York City’s subway system was inundated, leading to widespread infrastructure collapse, while the heatwave in Paris in 2003 overwhelmed health systems, tragically resulting in thousands of fatalities. However, the solution might not lie in building taller skyscrapers or expanding cities outward—many cities are now looking underground.

Below the surface, a wealth of untapped potential exists, offering innovative ways to combat climate challenges and promote urban resilience.

The Underground Advantage for Climate Resilience

Urban centres face numerous challenges as climate change escalates: rising sea levels, unpredictable weather patterns, and growing populations. These factors stress already burdened infrastructures, making traditional solutions insufficient.

In response, urban planners are increasingly turning to the underground—once thought of as mere space for utilities and transportation—as an essential part of building climate-resilient cities.

The underground presents an opportunity to reclaim space that might otherwise be used inefficiently, offering a new frontier for cities to adapt to a changing climate.

Take Singapore, for example. Through its Underground Master Plan, the city is planning to effectively turn the subterranean world into a valuable resource, integrating underground spaces for utilities, shopping centres, and even entire train stations. This aims to not only reduce surface-level congestion but make the best use of limited land, which is crucial for such a densely populated city. Similarly, Helsinki has been exploring subterranean solutions for managing digital infrastructure, energy use and waste, showing how cities can make the most of the space below ground to boost resilience.

Underground Mahak Agrawal - CityChangers.org
Mahak Agrawal. Image credit: Shannon Carroll Photography

Using the Underground for Flood Management

Flooding has become one of the most devastating consequences of climate change for cities worldwide. Storms are becoming more frequent and more intense, and rainfall patterns are more erratic, creating greater risks of flash floods and urban waterlogging. Cities built on low-lying land, such as Kuala Lumpur, Bangkok, and New York, are particularly vulnerable.

Kuala Lumpur’s SMART Tunnel (Stormwater Management And Road Tunnel) stands out as a groundbreaking solution to address these challenges. Completed in 2006 at a cost of USD $514 million, this 9.7-kilometre-long tunnel is the longest stormwater tunnel in Southeast Asia and the second longest in Asia. Uniquely, it serves dual purposes: managing floodwater and alleviating traffic congestion.

During moderate storms, the tunnel’s integrated design allows stormwater to flow through a designated channel without disrupting the motorway’s operation. In severe storms, the tunnel is closed to traffic, and its 3-million-cubic-metre storage capacity is utilised to divert and contain floodwaters, protecting the city from catastrophic flooding.

Constructed within an urban environment with complex karstic limestone geology, the SMART Tunnel exemplifies innovative engineering and risk management. Its success not only safeguards Kuala Lumpur from flash floods but also demonstrates how multi-functional underground infrastructure can transform urban resilience and mobility.

Singapore has also invested heavily in underground solutions for flood management. The Marina Bay Sands complex, for instance, uses advanced underground water retention systems to prevent flooding while maintaining the aesthetic beauty and functionality of the area. The city’s Stormwater Management Master Plan is designed to reduce flood risks by using subterranean solutions, like retention ponds and tunnels, that can handle excess rainwater while ensuring the continued development of Singapore’s urban landscape.

Marina Bay Sands, Singapore. Image credits: Mahak Agrawal

Below Ground in the World’s Biggest Cities

In New York City, the East Side Coastal Resiliency Project aims to protect Lower Manhattan from rising sea levels and storm surges. This multi-billion-dollar initiative includes an array of flood protection measures, including underground barriers and storage areas. With sea levels projected to rise by up to 1.5 feet by 2050, New York is leveraging subterranean space to secure its waterfronts while allowing for urban development and recreation above ground.

In Tokyo, one of the most ambitious flood control systems in the world operates deep below ground. Known as the Metropolitan Area Outer Underground Discharge Channel (MAOUDC), the caverns of this vast subterranean infrastructure help the city manage stormwater and prevent devastating floods.

The MAOUDC is a network of tunnels and reservoirs designed to capture excess rainwater during heavy storms. The system includes five massive underground reservoirs, each capable of holding millions of litres of water. The largest of these, the G-Cans Project, features enormous cylindrical shafts that reach as deep as 50 metres below ground, designed to divert water and prevent it from flooding the streets above.

The system works by channelling excess water through tunnels and into the reservoirs, where it can be safely stored until it can be released gradually into nearby rivers. In essence, Tokyo has turned its underground space into a massive flood water storage tank, reducing the impact of extreme rainfall and helping the city stay resilient in the face of climate change.

Cooling Cities From Below

Urban heat islands are one of the most pressing climate-related issues for cities today.

As cities become more developed, the heat generated by buildings, vehicles, and human activity causes temperatures to soar, exacerbating energy demands and negatively impacting public health. Cities around the world are now exploring innovative ways to mitigate heat through underground solutions that offer relief from the scorching heat above.

Tokyo has pioneered the concept of underground parks. In the bustling city where every square metre counts, the use of subterranean spaces to create green parks has helped mitigate the urban heat island effect while offering residents much-needed green space. These parks use cool underground air to regulate temperatures in the city, creating natural cool zones that reduce the need for energy-intensive air conditioning systems.

Similarly, in Paris, the city’s underground gardens are not just about beautification—they also serve as functional solutions to reduce heat in densely built areas. By planting vegetation underground, Paris is enhancing its ability to cool down its streets, increase biodiversity, and improve urban air quality. These green spaces help combat the urban heat island effect while also contributing to the city’s ambitious climate goals.

Saving Space, Saving Energy

Even in cities like New York, where space is at a premium, innovative projects like the Oculus at the World Trade Center showcase how underground architecture can reduce energy consumption while improving the public’s comfort.

The Oculus incorporates natural ventilation and green design elements, including below-ground areas that help regulate the overall temperature of the surrounding space. It’s a prime example of how underground spaces can provide sustainable, cooling benefits even in densely packed, high-traffic areas.

Oculus, New York. Image credits: Mahak Agrawal.

Energy Efficiency and Sustainable Infrastructure Below the Surface

Energy efficiency is one of the central tenets of any climate resilience strategy. Underground spaces, with their natural insulating properties, offer opportunities for cities to lower energy consumption and reduce carbon footprints. These spaces can house energy-efficient systems, from renewable energy storage to sustainable data centres, significantly reducing the energy required to run a city.

Take Iceland’s use of geothermal energy in Reykjavik. The city taps into underground sources to provide sustainable heating and electricity, significantly lowering its carbon emissions.

Switzerland’s Hagerbach Underground Data Centre is another impressive example. By using the natural coolness of the earth, the data centre reduces the need for traditional air conditioning, cutting energy consumption and costs.

London, too, is exploring underground energy storage systems that store excess renewable energy for later use. This underground infrastructure helps balance energy demands and offers a sustainable solution for cities transitioning to greener energy sources.

Moving Underground

Transportation is one of the most significant sources of emissions in cities. As urban populations grow, the demand for efficient, low-emission transport systems becomes even more critical. Underground transport offers a cleaner, more efficient alternative to surface-level traffic.

In New York, the Second Avenue Subway is a much-needed extension of the city’s underground network, helping to alleviate overcrowding and reduce the number of cars on the road. Similarly, Los Angeles is exploring underground rail systems, like the proposed LA to San Francisco Hyperloop, which promises fast, clean, and energy-efficient travel, reducing the need for long car journeys.

By prioritising underground transport, cities can reduce congestion, cut emissions, and improve air quality—proving that innovation beneath the surface can make a tangible difference.

Policy Leadership for Underground Space Use

Building resilient cities through underground infrastructure demands vision and strong policy frameworks. Cities like Singapore, Helsinki and Hong Kong have emerged as leaders in this field, each showing how strategic governance can unlock the full potential of subterranean spaces.

Singapore’s Urban Redevelopment Authority (URA) has been a pioneer in advocating for underground development, recognising that the land available on the surface is limited and increasingly valuable. The URA’s approach integrates subterranean infrastructure into long-term urban plans, ensuring that underground spaces contribute to the city’s sustainability goals.

Helsinki has taken an innovative and forward-thinking approach by establishing a “City of Caves.” Through meticulous urban planning, Helsinki has transformed its underground into a multifunctional space that hosts everything from data centres and sports facilities to water treatment plants. The city has mapped over 400 underground spaces and created a comprehensive plan that integrates these facilities into its urban resilience strategy. By moving critical infrastructure below ground, Helsinki reduces its vulnerability to harsh winters and extreme weather while also preserving the surface for green spaces and recreational use.

In Hong Kong, where land scarcity and high population density present unique challenges, policymakers have adopted a similar approach to optimise urban space. The city’s government has developed a strategic master plan for underground development, aiming to free up valuable surface space by relocating utilities and storage facilities underground. By prioritising underground development in densely populated areas, Hong Kong alleviates congestion and makes room for more liveable public spaces, enhancing overall quality of life.

These cities are setting a global standard in sustainable and strategic underground development.

Rethinking Cities: A Call to Look Below the Surface

As cities around the world grapple with the realities of climate change, urban planning needs a shift in perspective. The underground offers cities a unique opportunity to address climate impacts head-on. From managing floods to creating energy-efficient spaces, underground infrastructure can unlock a host of solutions that are both sustainable and resilient.

By rethinking urban planning to include subterranean spaces, cities can harness the earth’s natural resources and create smarter, more sustainable environments. The time to act is now. Governments, urban planners, and architects must work together to rethink urban design, integrating underground spaces into the fabric of cities.

This is why I started All Bits Count, to show (genuine and wannabe) change-makers that small changes, like incorporating underground solutions, can collectively make a big difference in addressing climate change and creating more resilient urban spaces. The transition to sustainable cities is not just about big investments but about smart, forward-thinking solutions that harness all available resources, no matter how deep below the surface.

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