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Urban forests

Lyon

28 January 2021

Elected Capital of Biodiversity in 2019, Lyon Métropole appears today to be one of the most commited communities in the fight against the effects of global warming thanks to its policy in favor of wooded areas.

 

Lyon Métropole was thus the first French city to integrate to its local urbanization plan a 30% vegetation coefficient, which is required for all new constructions, half of which must be in open ground to allow the growth of large trees.

 

At the same time, the “Grand” Lyon has adopted a Tree Charter, based on an urban forestry concept, which aims to reclaim a green agglomeration and works for reconciliation between nature and city. Following the adoption of this charter in 2000, the number of trees in the public areas of Lyon Métropole has multiplied by 2.4, gpi,g from 42,000 trees in 1990 to more than 100,000 today.

 

The “Canopy Plan” of Lyon is centered around 4 axes : to perpetuate and develop tree urbanization and heritage, to promote the well-being and mobilization of citizens, to unite professionals around the plan and to improve knowledge and development of new practice. It includes 25 actions which all contribute to protect and further develop the urban forest in the territory of Lyon Métropole. This plan aims to increase the urban canopy* to 30% by 2030.

 

The fight against the phenomenon of urban heat is at the heart of the “Grand” Lyon’s policy. This islet phenomenon is explained globally by the hyper-minerality of the cities, the darkness of the materials used absorbs the heat during the day** and releases it at night, the impermeability, and the lack of vegetation. Thanks to trees, local authorities hope to lower temperatures by several degrees. But not only thanks to trees, also and above all thanks to evapotranspiration***. To achieve the natural air conditioning effect, three layers are necessary: grasses on the ground, shrubs at breast height and leaf cover at the top level to promote the vertical exchange between air and water.

 

For the comfort of its citizens, Lyon Métropole made available to the public an interactive map of fresh places to find refuge in case of hot weather.

 

Lyon’s policy does not stop at planting trees. It is indeed a global urban policy considering all the factors allowing this wooded urbanization to last over time. The issue of water supply for green spaces was thus largely settled during the re-development of Garibaldi street. The old Vauban underground hopper has been transformed into rainwater tanks that can be used to clean the roads as well as supplying water for green areas.

 

Furthermore, the Métropole started to plant a urban forest following the Miyawaki method in the Duchère area un fall 2020.

 

So many projects that makes Lyon Métropole a sustainable and resilient territory that will, in the years to come, offer a more favorable environment to its inhabitants facing the rise of temperatures. The most pessimistic scenarios announcing that Lyon’s temperature in 2100 should be around Alger’s one today.

 

 

*The urban canopy corresponds to the tree canopy of a city. The canopy index, a tool developed by researchers at the Massachusetts Institute of Technology (MIT), is a measure that expresses the percentage of land covered by the tree canopy.

**More and more cities around the world have made the decision to repaint roads and roofs of buildings in white or blue because these light colors reflect better the sun’s rays allowing temperatures to be reduced. According to the authorities of the city of Los Angeles for example, streets covered with white coating are on average 5 to 7 degrees cooler that other streets in the city.

*** The water absorbed by the roots is then released as water vapor into the leaves, creating a cooling effect.

 

Picture 1: Vegetation in Garibaldi Street, Lyon ©D.R.

Picture 2: Vegetation and slow traffic in Lyon ©D.R.

Picture 3: Grand Parilly in Vénisseux project in which more than 700 trees will be planted and more than 2000 transplants. ©D.R.

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