Why we must leverage green and blue infrastructure to make cities more resilient to climate change

From underwater streets to blistering pavements, cities are living the future of climate change.

In 2023 alone, weather-related disasters displaced 7.7 million people globally. Across the world, urban areas are warming about twice as fast as the global average due to the urban heat island effect, combined with rapid urbanization. Likewise, according to NASA, extreme weather, including floods, has doubled in intensity and frequency over the past five years compared to the 2003–2020 period, fueled by the onset of climate change.

In response, urban governments are doubling down on ‘grey’ infrastructure: sea walls, levees, flood pumps and drainage tunnels. These traditional systems, while useful, are increasingly being pushed beyond their limits. Crucially, they don’t address the social determinants of vulnerability that determine resilience and recovery capacity.

To adapt effectively, cities must expand their use of different types of infrastructure. A growing body of research shows that 'green' and 'blue' infrastructure - urban parks, wetlands, bioswales and water plazas - mitigate physical risks and foster the social cohesion critical to surviving and recovering from crises. These systems should not be considered optional. They are central to how we build cities that can withstand the next disaster and recover stronger from it.

Grey infrastructure is engineered to control or even resist nature, not to adapt to it. As climate change and natural disasters accentuate, this rigidity becomes a liability.

New Orleans offers a sobering example. In 2005, Hurricane Katrina overwhelmed its levee system, resulting in over 1,800 deaths and $125 billion in damage. What made matters worse was that development had replaced natural buffers, like wetlands, which historically absorbed storm surges.

Similarly, Jakarta has spent billions on concrete flood barriers and pumps, yet the city still floods regularly. The city is sinking due to excessive groundwater pumping and building weight, with land subsidence rates being 5-10 cm/year, exacerbated by about 40% of areas being below sea level. This subsidence worsens flooding and reduces the effectiveness of concrete barriers, deeming them somewhat irrelevant.

In contexts like these, 'grey' defences also risk providing a false sense of security, encouraging construction in vulnerable areas. Once breached, their failure is often catastrophic, as they are expensive to maintain and difficult to adapt to worsening climate change.

Perhaps most importantly, they do little to address the social dynamics that determine who gets neglected in the face of disaster.

Contrasting this approach, nature-based solutions, often categorized as ‘green’ infrastructure, such as parks, trees, and green spaces, and ‘blue’ infrastructure, such as lakes and coasts, offer a fluid, adaptive and integrated approach to resilience.

‘Sponge cities’, for example, offer natural solutions to issues such as floods and sea-level rise by using vegetation and natural riparian flows to work with nature, not against it, absorbing the shocks and stresses of natural disasters. Likewise, in Basel, ‘green roofs’ have offered a mix of social and environmental benefits, concurrently enhancing urban biodiversity and urban cooling.

A particularly transformative example is the Big U Project in lower Manhattan - a nature-based ‘build back better’ solution to the impacts of Hurricane Sandy in 2012. This project is a 10-mile protective system around lower Manhattan, which combines berms, elevated parks and green spaces to create greater coastal resilience than that offered by the standalone ‘grey’ seawall that used to protect lower Manhattan.

Importantly, this doesn’t just mitigate the physical risks of natural disasters, it also provides public spaces that support health and social inclusion, instead of segmented, incohesive social dynamics. Likewise, the aforementioned ‘green roofs’ provide communal gathering spaces, enhancing social connectivity.

In this sense, 'green' and 'blue' infrastructure are not just about combatting physical risks, they also provide the social pre-conditions for resilience and recovery.

It is critical that green and blue infrastructure offer social cohesion co-benefits, as social cohesion is an important missing link in resilience and recovery to disasters.

Research by Daniel Aldrich shows that neighbourhoods with stronger social ties had significantly lower mortality rates during Japan’s 2011 earthquake and tsunami. Aldrich’s findings reveal that access to public spaces and community institutions was more predictive of survival than the height of sea walls, which was enabled by an investment in social infrastructure. This includes communal 'green' and 'blue' spaces, as well as libraries, community centres, schools and religious sites.

In this sense, Aldrich argues that social capital should be considered as a key determinant of resilience and recovery, cultivated over time and generated through shared spaces and inclusive urban design.

This can be largely explained by the fact that people in connected communities share information, check on one another and mobilize faster. These soft systems don’t just save lives, they accelerate recovery.

Unfortunately, many cities still favour physical assets and 'grey' infrastructure, belying the evidence that highlights the risks of over-reliance on such infrastructure.

Cities don’t need to choose between concrete and nature - they need to integrate them. Hybrid solutions that combine the reliability of engineered systems with the adaptability of ecosystems can offer layered protection.

These approaches don’t just mitigate risk, they provide daily benefits: cleaner air, better mental health, biodiversity and a stronger sense of community.

The urgency of climate adaptation demands more than bigger walls and better pumps. It requires a fundamental shift in how we define and invest in infrastructure. 'Green' and 'blue' infrastructure is not just environmental policy; it is disaster preparedness. The strength of our social ties is not a soft benefit; it is a core component of urban resilience.

By broadening the scope of what counts as infrastructure, we can build cities that don’t just survive disaster, but recover faster and more fairly. In an age of cascading risks, that’s not a luxury, it’s a necessity.

This article is part of the World Economic Forum’s ongoing work on sustainable cities, systemic risk and climate adaptation.