High on a roof in New York or a building in Milan, at ground level in the desert in Riyadh or in the streets of Medellin: green sites have flourished in major cities around the world.
Bringing nature back to the city: today, everyone agrees, while 70% of greenhouse gases (GHGs) come from urban areas, heat waves are increasing from Moscow to Vancouver, and warnings pollution is repeated from Paris to New Delhi.
Regardless of the pace at which GHG emissions are reduced, the devastating effects of global warming on nature and living things will accelerate and become painfully palpable long before 2050, according to a draft report by UN climate experts recently obtained. by AFP.
In a global momentum, town planners, architects, landscapers, pushed by a public in search of well-being and elected officials in search of attractiveness, are storming projects, from simple flower boxes on the sidewalks to the craziest buildings.
Greening cities is a fairly new idea, experts say.
The urban model began to change in the late 1990s in the era of sustainable development, far from the massive urbanization of the post-war years and their share of functionalist housing, commercial areas, urban ghettos and queen cars.
It developed at the start of the 21st century, in the era of global warming, at the rate of alarming reports from the Intergovernmental Panel on Climate Change (IPCC).
Thanks to green walls and roofs, the temperature in canyon streets during the hottest month in nine cities around the world can be reduced by 3.6 to 11.3 ° C at the hottest hour, according to the report " Nature en ville "from the French Ecological Transition Agency.
But are all projects equal?
"For a project to be virtuous, it must respond to a maximum of functions", lower the temperature by several degrees, preserve biodiversity, improve the well-being of inhabitants, generate awareness, notes Jean Haentjens, co-author of the book "Eco-urbanism".
It must also "respond to the desire of the public, be designed according to the environment, adapted to the social context, offer proximity" to residents, continues the eco-urban planner.
Futuristic garden in Singapore
The Gardens by the Bay site is the landmark of Singapore, the city-state attraction near the new business district.
© Roslan Rahman, AFP
Giant trees in vegetated concrete, a magical garden and a mountain in a greenhouse: the Gardens by the Bay site is the emblem of Singapore, the attraction of the city-state near the new business district.
Its 18 impressive "Super Trees", covered with lush vegetation, reach 25 to 50 meters high, with solar panels at their head.
Under its huge greenhouses made of steel and glass, the Flower Dome is home to a colorful botanical garden of tens of thousands of rare plant species from five continents and the Cloud Forest, an artificial mountain with its waterfall and plants that grow in it. Usually at 2000 m altitude.
The site, opened in 2011 on 101 hectares, won the World Building of the Year award the following year.
But in terms of environmental interest, experts remain skeptical.
"Why make concrete trees when you can have real ones?" Asks the author of the book "Habiter le monde", Philippe Simay.
"They are super-objects (...) without ecological interest, a disneylisation of nature."
"Un coup de com '", abounds Claire Doussard, planning teacher and researcher associated with the French National Center for Scientific Research (CNRS).
"We have demonstrated a technical know-how which contributes to the influence of Singapore" but, she says, it also contributes to "the awareness of the public" who come in droves to visit this nature threatened by climate change.
Rooftop culture in New York
Visitors on the green roof of the Brooklyn Grange building, in New York, on May 23, 2021. © Ed Jones, AFP
In the middle of the buildings, tall chimneys, four-lane roads below, the Statue of Liberty in the distance, fields of radishes, leeks, salads on a plot of over 14,000 m2.
We are on one of the largest cultivated rooftops in the world, on the 9th floor of a building in Sunset Park in New York, at the Brooklyn Grange.
Here, we cultivate, we sell, we buy, we walk, we help city dwellers to "find a connection to nature".
And in doing so, we lower the heat, improve air quality and enrich biodiversity, explain the founders of this pioneering project.
Launched ten years ago, it is now available on three New York rooftops with a total area of over 22,000 m2 where more than 45 tonnes of organic products are grown per year.
In general, the logistical aspect is heavy for this type of culture, notes Claire Doussard, director of the publication of the book "(re) Penser la ville du XXIe siècle".
It is necessary to insulate, to mount the ground, the water, to lower the salads ... "These farms must be profitable because there are many constraints", she notes.
A vertical forest in Milan
The architectural complex called "Vertical Forest", designed by Studio Boeri in the modern Porta Nuova district in Milan, June 2, 2021. © Miguel Medina, AFP
Two hectares of high forest as well as 20,000 plants and trees are spread over two buildings in the middle of the Milanese district of Porta Nuova.
It is called the "Bosco Verticale" ("vertical forest" in French).
On each balcony grow dozens of plants or trees, chosen and positioned according to their resistance to the wind and their preferences in terms of light or humidity.
This project was "born from my obsession with trees" and from a reflection on "the way in which they could become an essential component of architecture", explained in 2017 to AFP its architect, Stefano Boeri.
The idea was also to build a building which could "contribute to reducing the pollution of the city".
Completed in 2014, the "Bosco" received in 2015 the title of the most beautiful and innovative building in the world by the Council on Tall Buildings and Urban Habitat (Chicago).
But it is also called "bling bling", with its apartments which can reach 15,000 euros per m2, "gadget" and "little virtuous".
A vertical urban farm on the outskirts of Copenhagen
Plants grown in the vertical plant farm "Nordic Harvest", located in Taastrup, on the western outskirts of Copenhagen.
© Thibault Savary, AFP
In Copenhagen, the "Vertical Farm" grows salads and herbs at the rate of 15 harvests per year, in artificial light only.
Some 7,000 m2 filled with shelves 10 meters high on 14 levels, lit by a total of 20,000 LED bulbs.
Here, the seeds are transported by robots which roll between the aisles and we garden from the top of a freight elevator.
Located in a Taastrup hangar in the industrial area of Copenhagen, this urban farm was inaugurated in December by the Danish start-up Nordic Harvest.
"We are proving that it is possible to move part of agricultural production to cities," says its CEO, Anders Riemann.
It is the "high tech" project par excellence, notes Philippe Simay.
"It is very expensive in maintenance, in skilled labor, you need lights on 24 hours a day. We are in the fantasy of production with people who say 'we are going to feed the cities'", points out the specialist. .
Reforestation in the desert in Riyadh
Workers plant trees near a highway in Riyadh, Saudi Arabia, March 29, 2021 © Fayez Nureldine, AFP
Today, we only see shoots lost in the middle of multi-lane highways and gigantic interchanges.
In the distance of the dunes.
In the air, pollution, dust and heat.
But by 2030, the "Green Riyadh" project plans to plant 7.5 million trees and create 3,000 urban parks to make the Saudi capital a greener city.
An 11 billion dollar project that will require one million cubic meters of water every day, recycled through an underground irrigation system reusing wastewater, it is promised.
"Reintroducing trees into the desert is very virtuous, we gain in refreshment", estimates Cédissia About.
"The question will be whether they use phyto products that scare away birds and insects when the priority issue is to increase biodiversity."
Green corridors in Medellin
People walk in a green corridor in the Poblado district of Medellin, Colombia, June 13, 2021. © Joaquin Sarmienta, AFP
Urban roads, previously deprived of nature, have been transformed into 30 "green corridors" with trees and flowers, "connected" in a network to already existing green spaces, from public parks or lawns to private gardens.
A green continuity that has enabled Medellin, Colombia's second city, to lower the temperature by two degrees, to help purify the air, to bring back bees and birds, to involve the inhabitants, to create jobs in gardeners, boasts a video from the municipality that has been supporting the project since 2016.
The project has received multiple awards - it received the Aschden Award and the C40 Cities Bloomberg Philanthropies Award in 2019 - for having "improved biodiversity", "reduced heat", "contributed to the well-being of citizens", according to the C40 website Cities.
"It is one of the best examples (of revegetation), driven by a policy, which increases biodiversity, with a social dimension", comments Philippe Simay.
"It's better when you think on a large scale in terms of ecological continuity, it has a real impact", confirms Claire Doussard.
"There was a real reflection on the scale of the city, on the species chosen, the habitability, the constraints."
A jungle in buildings in Chengdu, China
Green buildings in a residential area of Chengdu, southwest China, July 12, 2021. © AFP
In Chengdu, China, eight buildings have been revegetated with plants growing on apartment terraces in a residential area in the capital of Sichuan.
This experimental project was launched in 2018 and called "Qiyi Forest Garden".
In places, it feels like a cabin perched high in a tree, in the middle of the rainforest and the chirping of birds.
The quality of "the air is good when we wake up in the morning and seeing these trees full of greenery makes us old people good," says resident Lin Dengying.
Elsewhere, nature seems to have reclaimed its rights, the jungle has invaded the balconies, sprawled out on the walls, slumped from one floor to another.
In September, the semi-official daily Global Times reported a low occupancy rate of the 826 apartments, which tenants said was due to the presence of numerous mosquitoes.
For this type of project, it is certainly important to think about the environmental impact but it is necessary to take into consideration "maintenance" and "habitability", notes Claire Doussard.
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