Back to nature: restoring ecosystems to shield cities from climate threats
As climate threats grow, cities are turning to Nature-based Solutions to safeguard urban life. By restoring natural ecosystems, they enhance resilience while reconnecting people with nature.
In 1992, the city centre of Sarcelles, France, was submerged under a meter and a half of water after torrential rains. The culprit? The Petit Rosne River. Cemented, buried underground, it reclaimed the urban space it once freely flowed through. Years later, in 2014, the city began an ambitious project to dismantle the road and let the river breathe again. Today, the Petit Rosne meanders naturally through Sarcelles, creating green spaces for residents and habitats for wildlife, while also acting as a flood control mechanism. "This is an example of a Nature-based Solution (NbS) in an urban environment that I like to mention because it simply involves restoring nature," says Susanna Gionfra, Senior Officer for Nature-based Solutions at the International Union for Conservation of Nature (IUCN). "Once the initial expense is addressed, there isn't much else to do: animal and plant species reclaim the area without much effort from humans."
This simple yet effective approach embodies the power of Nature-based Solutions—sustainable interventions that harness nature's power to tackle societal challenges while enhancing human well-being and biodiversity. And as cities face increasing threats from climate change, these solutions are emerging as crucial tools for safeguarding critical infrastructure and building urban resilience. According to the United Nations Disaster Risk Reduction (UNDRR), NbS are actions "to protect, sustainably manage and restore natural or modified ecosystems, which address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits". The concept first emerged in the early 2000s, promoted by IUCN and the European Union as a response to climate change and disaster risks. Today, they are being adopted worldwide to mitigate carbon emissions, improve urban liveability and prevent catastrophic events. Indeed, according to the International Institute for Sustainable Development, Nature-based Solutions could contribute to 37% of global CO2 mitigation targets by 2030.
Yet, as cities grow and climate threats inensify, a new question arises: can they protect critical urban infrastructure—the systems essential for societies to function during and after disasters, such as water supply, healthcare, energy and telecommunications?
To explore this potential, the European project NBSINFRA is focusing on using NbS to protect urban critical infrastructure. "During catastrophic events such as flash floods, wildfires or earthquakes, critical infrastructure is the main support for societies during and after the event," explains Elisabete Teixeira, Ph.D. in Civil Engineering at the University of Minho in Portugal and coordinator of NBSINFRA. "It needs to be as efficient as possible, but it also suffers from such events, so they need to be protected."
The project is being tested in five city-laboratories across Europe—each facing unique environmental challenges. For example, in Aveiro, known as the "Venice of Portugal" for its intricate canal system, flooding is a persistent threat. "The problem is that the canals are connected to the river and the ocean, and freshwater also flows into them. We are studying NbS that can, in the event of a flash flood, retain water or minimise the velocity of the water in the river," says Teixeira. Meanwhile, in Prague, NbS solutions are being developed to tackle both heatwaves and heavy rainfall. Part of the project involves constructing hybrid green roofs fed by greywater and rainwater. "Green roofs in average reduce rainwater runoff by 50% and contributes to mitigating heat waves through water evaporation," explains Michal Sněhota, Associate Professor at the Czech Technical University and leader for NBSINFRA in Prague.
While NbS offer promising solutions, their implementation is not without challenges, particularly in urban areas where space is limited, and costs are high. "In cities, they have a higher cost. What we recommend is to implement them where there is already a foundation, just like in Sarcelles, by restoring and renaturing green areas," says Gionfra. "A key challenge remains the higher maintenance costs associated with NSB compared to conventional grey infrastructure. To address this, a cost-benefit analysis should always be conducted to quantify long-term gains in resilience, ecosystem services and social wellbeing against the initial and operational expenses" say Sněhota and Licia Felicioni, architect and Ph.D. researcher at Czech Technical University. For example, green roofs require regular maintenance, including fertilization and weeding, which can be costly. However, these costs could be outweighed by the benefits if implemented on a large scale, with a radical shift in urban development perspective. Economic challenges are significant as well, as public funding alone may not suffice. "We see the private sector as playing an important role in the upscaling of Nature-based Solutions, together with the public sector," adds Gionfra. Moreover, effective NbS implementation requires a paradigm shift in urban planning. "Their impact is limited if we do not change our perspective to integrate them into broader contexts of interconnected green infrastructure. Additionally, there is the potential challenge with the misuse of the NbS term: in this context IUCN has been working to support the design and verification of Nature-based Solutions and has produced a global standard for this purpose," explains Gionfra.
While momentum for NbS is growing, Zahra Amirzada, Consultant on Natural Sciences at the UNESCO Liaison Office to the EU, highlights ongoing challenges, including policy coherence, funding and public perception. Key priorities involve developing standardised evaluation frameworks and educating the public about the benefits of NbS. In response, UNESCO is actively promoting advocacy campaigns and capacity building programmes while supporting NBSINFRA. "Another challenge is the need for robust scientific evidence and long-term monitoring. While the body of research on NbS effectiveness is growing, policymakers often demand quantifiable impact assessments before committing large-scale investment. This is why we support standardised evaluation frameworks that provide common indicators for measuring their impact," says Amirzada.
Despite these challenges, NbS enhance urban resilience by mitigating risks from natural hazards while also creating vibrant green spaces that improve social life and well-being. In Aveiro, green areas with soft mobility are being studied near waterways to contain floodwaters while offering recreational areas. "The idea is to create an ecosystem that is sustainable and pleasant for people," says Teixeira. Similarly, in Prague, the green roof not only manages rainwater but also provides a corner of beauty and an urban oasis that cools the building during heatwaves.
Crucially, NbS contribute to an often overlooked yet powerful benefit: happiness. Studies show that access to green spaces boosts mental health and wellbeing. Nature prescription is becoming more popular, and its positive impact on mental and physical wellbeing has been proven. During the pandemic, urban residents worldwide experienced the restorative power of nature firsthand. As cities continue to grow, integrating NbS offers a unique opportunity not only to protect critical infrastructure but also to create happier, healthier urban environments.
Contacts:
Project coordinator:
Elisabete Teixeira—UMINHO
Project Management Officer:
Alice de Ferrari—ICONS
Project website: https://nbsinfra.eu/
LinkedIn: https://www.linkedin.com/company/nbsinfra/
Provided by iCube Programme