Hauts-de-Seine: Meudon innovates to adapt the city to climate change

Climate change reinforces the need to better locally identify in large cities the areas most prone to the urban heat island effect (ICU), an aggravating factor during a heat wave.

The ICU, a climatic phenomenon

A climatic phenomenon, the urban heat island is characterized by temperature differences: these temperatures are higher in urban areas than in surrounding rural areas. The urban heat island is generated by the city, its morphology, its materials, its natural, climatic and meteorological conditions, its activities. In return, it influences the city’s climate (temperatures, precipitation), the levels and distribution of pollutants, the comfort of city dwellers, and the natural elements of cities. The urban heat island is an aggravating factor in heat waves and in particular heatwave episodes. However, with climate change, heat waves and heatwaves tend to increase. The urban heat island phenomenon amplifies these climatic episodes, particularly at night, by limiting nighttime cooling in the city. We can thus observe significant temperature differences between Paris and rural areas: up to 10°C during the exceptional heatwave of 2003.

An issue in Hauts-de-Seine

It is therefore a strategic urban data to take into account in the design and management of the city. Highly urbanized, the Ile-de-France region is particularly vulnerable to this phenomenon. According to figures from the Paris Region Institute, more than 3,685,000 Ile-de-France residents, or 31% of the regional population, reside in islets considered highly vulnerable to heat, including 845,000 people particularly sensitive to this phenomenon due to of their age: children under 5 years old and people over 65 years old. In Hauts-de-Seine, the mapping of heat islands and cool islands (IFU), drawn up by the R&D department of Verdi Ingénierie, shows large disparities between the different municipalities in the department. Thus, 92% of the inhabitants of Levallois-Perret, with nearly 68,000 inhabitants with a density of nearly 28,000 inhabitants/km2, reside in ICUs. On the other hand, in Asnieres-sur-Seine, with 88,500 inhabitants and a density of 18,300 inhabitants per km2, the rate of exposed buildings is lower, still affecting 71% of the population. The territory therefore presents strong disparities within densely populated cities, mainly caused by very different rates of vegetation. These disparities are even more marked for municipalities with lower urban density. Chatenay-Malabry, Chaville, Clamart, Garches, Le Plessis-Robinson, Marnes-La-Coquette, Meudon, Rueil-Malmaison, Saint-Cloud, Sceaux, Sèvres, Vaucresson, Ville d’Avray are distinguished by the marked presence of islets of freshness, sometimes very extensive. On the other hand, cities like Levallois-Perret, Vanves, Puteaux, Montrouge, Malakoff, La Garenne-Colombe, Issy-Les-Moulineaux, Courbevoie, Clichy, Boulogne-Billancourt have numerous and extensive areas of urban heat islands and too many few cool island areas.

Meudon, a city committed to the climate transition

Mapping these ICUs and IFUs is an essential tool for piloting an effective fight against global warming in urban areas. This is the challenge started by the city of Meudon, which uses simulation technology to identify urban heat islands (ICU) present on its territory. This unique experience has been on the city’s agenda since September 2024. It is part of the environmental policy of a municipality resolutely committed to the climate transition. The city is developing its territory by reducing its carbon footprint. It lists the fight against global warming and the preservation of biodiversity as its priorities. To this end, Meudon is increasing the number of operations to dewaterproof public spaces. Since 2019, 20,000m² have been de-waterproofed

Promote the development of urban cool islands

Not only does this policy help promote the infiltration of rainwater, but it also helps reduce heat islands and therefore gain up to 5°C during heatwaves. Place Rabelais and its vegetated pits which connect the bases of trees illustrate this policy. This fight against land artificialization also applies to municipal cemeteries, traditionally very mineral spaces. The city grassed the paths, greened the walls and planted trees. At the same time, ambitious projects to transform mineral spaces into islands of greenery are being carried out. In progress or in the future, the greening of the Tony de Graaff and Simone Veil squares, and the square in front of the Center for art and culture demonstrates the city’s commitment. The fight against heat islands is also taking place in schools. Each year, two schoolyards are greened to provide children with a more pleasant environment. With 8,000 trees recorded, including 400 planted in 2023 and 200 remarkable trees, the city has a very rich natural heritage. It is the result of a proactive policy of preserving and adapting vegetation. This green heritage promotes the development of urban cool islands.

Monitor the evolution of urban heat islands

Through its partnership with Dassault Systèmes, Meudon uses simulation technology to create the virtual twin of three public spaces, where development projects are underway to transform them into greener spaces. The simulations aim to calculate and evaluate air circulation and temperature in these three sites. They take into account different weather conditions at different times of the day by integrating buildings, trees, roads, soil, wind, sunlight and other factors into the virtual twin. These simulations will shed light, in the light of science, on future development directions for the city’s public spaces, while providing municipal officials with indications regarding the mitigation of these heat island phenomena. In town, the stored heat is greater. The urbanization model, floor coverings, lack of vegetation or water in public spaces are all factors that prevent urban space from cooling. High buildings and the density of walls slow down air circulation, and the building stores heat. Building materials such as concrete, brick or stone easily capture heat during the day, through solar radiation, and gradually release it into the atmosphere at night, preventing the air from cooling, underline the experts from Météo- France…

The department is banking on green islands

In order to combat heat islands, the department is gradually reorganizing public college courses. Greener and more welcoming, the new generation courses also contribute to improving the working environment of the 74,000 Altosequan college students. This ambitious project is included in the department’s 2030 Agenda.

40 million euros is the budget invested by the Hauts-de-Seine department for its middle school courtyard greening program. Launched in 2022, following consultation with middle school students, this system aims to improve students’ daily lives, provide relaxation areas for teachers and staff housed on site and adapt to environmental issues. Indeed, it is an effective response to the fight against urban heat islands and the reduction of rainwater input to the sanitation network. A pilot establishment, the Jean-Macé college in Clichy-la-Garenne inaugurated its green island at the end of 2021. By 2027, 38 public colleges in Hauts-de-Seine will be redeveloped.