Learning about trees: How can nature solve urban challenges?

Friday, March 6, 2020

The Zurich Flood Resilience Alliance promotes alternative ways to reduce flood risks and build communities’ resilience. Nature-based solutions are one of the most promising approaches to achieve these goals, thanks to the multiple co-benefits they can offer. Still these interventions are relatively uncommon, especially in cities.

Cities: key actors for climate change

More than half of the world’s population now live in cities, and the trend is not expected to change. Growing cities often bring with them increases in challenges such as pollution, noise, stress, heat islands, as well as increased risks of floods and other hazards. At the same time, climate change exacerbates the frequency and intensity of hazards such as floods and heat waves, further degrading the wellbeing of those living in cities.

In this context of climate change, but also of urban specific challenges, the European Commission is currently supporting several research programmes focused on nature-based solutions, accounting for a total of 373 partners conducting research projects in more than 90 cities until 2024. 

I recently attended a training course on nature-based solutions in urban planning by the Re-Nature programme, one of these European Commission-funded initiatives, hosted by the University of Trento in Italy.

Nature-based solutions: a new concept?

The training started with an overview from Marcus Collier from the Trinity College in Dublin, who reminded us that while the “nature-based solution” concept appeared in 2010, it is heavily based on ecosystem services and green infrastructures, which are much more established approaches. The relatively new concept of nature-based solutions offers an interesting and catchy new perspective but we should avoid re-starting from scratch, and instead build on existing knowledge!

What should we consider when planning nature-based solutions?

Lynn Dicks from Cambridge University and Mario Balzan from the Malta College of Arts, Science and Technology then took us for a quick dive into biodiversity issues. They highlighted that more biodiversity generally leads to greater ecosystem services: diverse systems are usually more productive, more stable, and predictable (although they too can reach a saturation point).

On the second day of the training, Davide Geneletti from the University of Trento summarised 4 main components which need to be taken into account when designing nature-based solutions (NbS) to achieve specific ecosystem services: (1) the components of the NbS (for example: water, grass, trees, etc; but also specific species of flora); (2) the shape and size of the land, (3) the location and (4) the ecological pressure. This last one is probably the most challenging to grasp, as it refers to pressure from a dynamic environment. For example, the more polluted the area, the more significant is the effect of trees removing pollutants. However, if the level of pollution is too high, some trees might not survive. As a flood related example, bio dykes which can be useful in reducing risk up to a certain level of flooding might be destroyed in an extreme event.

We also had interesting discussions around challenges related to nature-based solutions: how they can generate adverse effects such as health problems (mosquitos reproducing in ponds, rats/monkeys invading the city due to re-greening), green gentrification (urban areas with parks become more expensive, meaning poorer people cannot afford the cost of living) and increased risks (for example, trees can get uprooted during a storm and block roads).

Bringing these insights to the Zurich Flood Resilience Alliance’s work

This led me to think more deeply about our work on natural capital within the Zurich Flood Resilience Alliance:

What could be some of the challenges associated with nature-based solutions in rural areas?


How could we take biodiversity into account more when designing nature-based solutions for flood risk reduction? Both in terms of how nature-based solutions for flood risk reduction contribute to biodiversity, but also, how biodiversity contributes to the functioning of NbS, thinking for example about synergies between species?

We definitely need more applied research to unpack the added-value of nature-based solutions to increase flood resilience. Bringing together biodiversity specialists, disaster disk reduction practitioners and integrated water resource management experts is critical to doing so. 

Special thank you to all the training organisational team and speakers: we also had great case studies from Chiara Cortinovis, Enzo Falco, Lorenzo Giovannini, Jarumi Kato Huerta, Susana Orta and Blal Adem Esmail on specific nature-based services and approaches to develop them; as well as field visits in Trento to directly test our learning.

Let’s keep the conversation going by sharing your thoughts and experiences in the comments section of this blog. 

You can also use the Portal Library to find a range of resources on the topic of nature-based solutions. 

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