RSK’s Cities of Tomorrow series explores the sustainable solutions available to us to create resilient and future-proof urban centres and the ways in which our family of businesses is responding to these needs. Access to green space is a vital part of this, and many city councils are starting to look towards urban greening initiatives. Stéphanie Eveno from ADEV, an RSK group company, speaks from experience on the topic, sharing the best methods to ensure a healthy green environment in our urban centres.
During the pandemic, two things became very clear: that going outside is very important for our health, both mental and physical, and that people who live in cities often spend more time outside of their homes than inside. This is especially true if space is limited, as is the case in many cities. So, any green, sustainable and future-proof city design will need to include public green spaces for its residents to enjoy.
Benefits for global warming, water management and wellness
Studies have shown that having access to outdoor greenery is good for our mental health and can help reduce anxiety and all the health problems related to this. There is plenty of evidence to show that greater access to green space is good for public health: so much so that the World Health Organization recommends all people reside within 300 m of a green space.
But on top of this, one of the problems with urban environments is that concrete is impermeable, and this means that when it rains, the water accumulates rather than draining into the soil below. This has big implications for flood risk management: now, when you plan to redevelop an area and turn it into residential space, one of the first questions the authorities ask is, “How are you going to deal with rainwater?” There is more awareness now that you can use green spaces to manage rainwater while also providing a multifunctional public area that benefits the people living there. The other problem with concrete environments is that the high thermal mass creates an ‘urban heat island’ effect in summer. Both the flood risk and the heat are issues that will become more prominent with climate change.
Urban greening should focus on soil
To make the most of the flood risk and heat control benefits, you have to start at the source: the soil. You have to bring good soil back into cities if you want healthy green spaces. And it isn’t just about the square metres on top, it needs to be deep enough so trees can fully develop a root system that can reach the water and nutrients and hold the ground together – crucial to mitigating flood risk. Usually in cities, you can see trees are under stress because of pollution, a lack of rain and a lack of water, bad soil and a lack of space below ground. But when you have the soil available for plants to grow well, you get the dual benefit of improved biodiversity as plants attract numerous insects and birds, so it pays for itself.
Smaller, very isolated green spaces, such as living walls and green rooftops that we have in places such as the Jardin Atlantique in Paris, are a positive addition. Whatever life we bring back through greenery is better than concrete. But to get the full benefit, we need deep soil that lets water drain all the way through.
The key to green cities is proper maintenance
A lot of regions have tried to re-green their cities. The municipality of Paris, which has only a small number of green spaces compared to other cities, recently announced a programme to plant 170,000 trees by 2026. This of course is a fantastic goal, but in practice, it could be difficult to achieve. Unless these new spaces are very well maintained, they could end up being blighted by littering, which is not only bad environmentally, but it also spoils what could have been a beautiful green space. And the thing about introducing new greenery is that it has to be maintained if it is to thrive. Sadly, a lot of newly planted trees end up dying soon after because the ground is too dry and they are not sufficiently watered.
There’s a period of 10–20 years during which the trees establish, when the benefits of new trees are not properly felt but when they require a lot of upkeep compared to the older trees that look after themselves. And this is where there is real opportunity: protecting and carefully keeping the trees that are already 50–100 years old is far more valuable to a city greening project. These are much more efficient at absorbing water and CO2 and are much hardier already.
The best time to plant trees was twenty years ago
In order to have a green, sustainable and healthy city, the first thing you should do is examine the existing greenery: look at the existing parks and ensure they are well maintained and managed. Only then start thinking about putting in new vegetation. The true goal for a sustainable city is to plan far enough ahead that you prevent the loss of greenery and soil in the first place, building your city around the green spaces rather than trying to put them back in once they are gone. Because ultimately, what will make a city resilient is protecting the life and greenery that we already have.
Stéphanie Eveno, General Studies and Technical Director, works for ADEV Environnement, a consultancy in Larçay, France and soon, Paris. It provides expertise to a range of clients, from biodiversity assessments to sustainable town and energy planning.