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Greening cities

Since the 1960s, cities have been facing unprecedented urban sprawl to meet the needs of an ever-growing urban population: demands for housing, transportation, activities, parking, etc. This transformation of the city has led to an artificialization that is hostile to living organisms, as highlighted in the second edition of the "Global Land Outlook", a UN report published on April 27, 2022, after five years of work on an international scale. Today, 40% of the planet's land is in an advanced state of degradation. One of the causes? Mass urbanization and the sealing of surfaces that hinder urban resilience to climate change, loss of biodiversity and the well-being of inhabitants.

Temperatures are rising in cities: many observations show that the temperature differences between urban centers and the surrounding areas average 4°C, but can reach up to 12°C. Artificialization and concretization of the soil are largely responsible. Indeed, dark surfaces, very frequently asphalt or concrete, can represent more than 40% of the surface of a city according to ADEME estimates. These surfaces absorb the sun's rays, and therefore heat, instead of reflecting it. The heat stored during the day is then released at night, which can contribute significantly to heat waves.

Urban heat island phenomena (UHI) have multiple impacts: on health, on the well-being of inhabitants, on the attractiveness of city centers, on energy consumption (due to air conditioning), on the resilience of infrastructures and urban networks, but also on fauna and flora.

Biodiversity is disappearing...and with it, the ecosystem services it provides. And yet, city dwellers benefit from many services provided by nature. In the city, the Foundation for Research on Biodiversity notes mainly climate, air and water regulation services, but also cultural services that are recreational (such as sports), educational (environmental awareness), and aesthetic. For more than 8 French people out of 10, the proximity of a green space is an important criterion in the choice of their place of residence.

Faced with these urban challenges, there are solutions. To better adapt to the effects of urbanization and climate change, cities are encouraged to renaturalize their soils. Renaturation consists in fighting against the loss of the living system, which is in fact suffocated under a paved or concrete surface. By implementing renaturation operations, communities ensure that the soil is balanced and that the surfaces are once again connected to the water table through a continuous, living soil that supports a rich ecosystem.

However, soil permeability does not always seem to be a priority in public policies, although the ecological and socio-economic benefits are numerous. We can mention for example

- Water runoff (rain, river, etc.) that prevents flooding

- Giving the living soil the water it needs

- Save money by reducing the drainage infrastructure

- Improving the living environment of city dwellers, especially since the Covid-19 crisis, which has generated a demand from residents for more nature in the city

- A better interaction between living species which is fundamental for the balance of ecosystems

- Reduction of heat island phenomena

- A reduction of air and soil pollution

According to the Ministry of Ecological Transition, in France, between 20,000 and 30,000 hectares of land are artificialized each year. Even more alarming, this artificialization is increasing almost four times faster than the population. Therefore, the fight against artificialization is one of the major axes of the Biodiversity Plan designed by the government and whose objective is to achieve "zero net artificialization", known as "ZAN", by 2050 according to the Climate and Resilience Law. To achieve this, it is necessary to limit as much as possible the consumption of new spaces and, when this is impossible, to "return to nature" the equivalent of the areas consumed.

To control urbanization, local urban plans (PLU) and territorial coherence schemes (SCOT) are tools that local authorities can use. These measures must be adapted to the local context, which must be reconciled with various public policies, including housing policy, which can encourage the mobilization of surfaces that have already been built up by promoting densification and the use of vacant premises and wasteland.

Cities are key players in the transition and are carrying out actions that demonstrate the effectiveness and innovation that the municipal level can bring to bear on the cross-cutting issues of the dual crisis of climate and biodiversity. Indeed, local authorities and their various actors (associations, municipal teams, universities, etc.) are the best placed to take into account the specificities of the field and to encourage the mobilization of citizens in the implementation of renaturation projects. Placing Nature at the heart of urban projects would contribute to reaching the +1.5°C objective defined by the Paris Agreement and in a way defined as more profitable.

It is estimated that more than 6,000 species or varieties of plants can find a place in the heart of an urban environment. A territory integrating 30% of natural spaces can thus reduce the collapse of species by 50%. In France, the "Grenelle de l'environnement" decreed in 2007 the implementation of an important "green and blue framework" aiming at preserving ecological continuities and constituting a national network of ecological corridors. Several frameworks are now integrated into the urban policies of more and more municipalities, as in Rouen for example. Through its "Rouen Naturellement" program, several frameworks have been instituted:

- a green grid: a network of vegetated areas

- a blue grid: connecting waterways and wetlands

- a brown grid: soil continuity

- a black grid: sectors where nightlife is encouraged by fighting against pollution

To renaturalize cities and celebrate biodiversity and urban well-being, communities are encouraged to follow successful initiatives such as the creation of shared gardens, parks, or urban agriculture programs. It is important to insist on actions that involve citizens in their own right. We could speak here of encouraging more eco-citizenship in the municipalities' renaturation programs. Indeed, redeveloping the territory is often not well accepted by the population, which is often suspicious of the work involved. The municipal teams in charge of these projects would gain by systematically integrating the inhabitants into their operations.

One example is the success of Strasbourg and its "Strasbourg, ça pousse" program. The initiative was born of a political will to reintegrate nature into the city by demineralizing and then revegetating public spaces (at the foot of facades and trees, sidewalks, etc.). Citizens are the main actors in the implementation of this project, which promotes, for example, social ties and shared gardening. The city has simplified the procedures so that residents can get involved in the development of a resilient and greener city. A map of the various initiatives (allotment, shared or school gardens, urban vegetable gardens, green sidewalks, composting points, etc.) is available on the website dedicated to the operation.

Something to inspire you?

Sources :

- Ministère de la Transition Écologique :

- Strasbourg ça pousse :

- Agence d’Urbanisme de la Région Nantaise :

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