2023-09-05 10:32:27
The darker a district, the more the heat island phenomenon is felt.
Why is Brussels affected by heat islands?
A study shows that air temperatures “are 3°C higher on average in the center of the Brussels-Capital Region than in its rural surroundings in summer”. This phenomenon is explained in particular by a very mineral urban center, with little vegetation, with impermeable soils that do not retain water, but also by a significant presence of thermal engine vehicles and air-conditioned buildings – which therefore reject hot air out.
This is mainly the case for the city center and the inner ring (municipalities located between the small belt and the large belt), which suffer from heat waves, while, unsurprisingly, the large parks, such as the Cinquantenaire and the Forêt de Soignes, are more temperate, more breathable areas, just like the southern districts of Brussels, which are less dense and more vegetated.
Only less than 10 kilometers separate the Etangs Noirs from the Sonian Forest. However, the degree of comfort goes from one extreme to the other.
The night is the time when the heat effect will be felt the most, when materials such as asphalt or concrete, very present in the city, let the energy of solar radiation accumulated during the day escape. Heat bubbles are created, with temperature differences of several degrees between the center and the surrounding rural areas.
Not everyone experiences the heat island in the same way
For this point, there are two aspects. A health issue first. In addition to being overwhelming, the event is therefore also dangerous for health. Respiratory problems, even death, can affect the elderly, those with allergies or even babies and young children. Not to mention the various discomforts, sleep disorders, headaches, etc.
Secondly, the population of Brussels is unequal in terms of the intensity of the heat island. In fact, the inhabitants of Brussels in the coolest districts earn 31% more than those in the warmer districts. The inhabitants of Vivier d’Oie, in Uccle, have a median income of 25,768 euros, even though the district is one of the coolest in the capital. The Marolles, right in the center and therefore on the front line facing heat islands, is considered one of the poorest, with a median income of 15,664 euros.
Affluent people are therefore better protected against heat waves, thanks to less dense, greener neighborhoods, or even greater financial means, which make it possible to better insulate homes in order to further counteract the harmful effects of a heat wave. .
How to fight against heat islands?
“Heat is a recent issue, which dates back ten years. It has become urgent to develop the city”, observes Pascale van der Plancke, in charge of coordinating the regional adaptation strategy at Brussels Environment. Mapping the blocks is a first step in identifying the areas to be prioritized and the neighborhoods that need them the most.
Planting trees is one of the solutions, for the shade provided and the cooling effect of the water released into the air by the leaves. Quite a challenge nonetheless in Brussels. An almost non-existent subsoil map prevents knowing the best areas, because gas, electricity, water, or public transport saturate the Brussels subsoil, preventing roots from developing well. THE Canopy mapwhich aims to “plant trees wherever possible”, launched the mapping of two sectors in 2020 to identify suitable places.
The solutions sometimes seem interdependent. There is no point in planting trees if the measure is not accompanied by good rainwater retention management. “The water must not go into the sewers, it must be able to infiltrate the plot to create an evapotranspiration phenomenon which will allow the plantations to reject water vapor into the atmosphere and refresh”, continues Pascale van der Plancke, who gears up on the PACE, the Air Climate Energy Plan adopted by the government of the Brussels-Capital Region in April. A plan to “improve the resilience of the territory by aiming for better soil permeability, integrated stormwater management, increased revegetation, etc.”.
There is a need to further clarify the coverage of public space and ventilate cities to allow prevailing winds to cool them.
Pierre Vanderstraeten
professor emeritus of architecture and urbanism at UCLouvain.
Two other concrete solutions are put forward by Pierre Vanderstraeten, professor emeritus of architecture and urban planning at UCLouvain. “We need to further clarify the coverage of the public space. The materials in the city are too dark and retain heat”. We can think of white anti-heat paint, or the installation of a reflective film on the roofs to reduce the temperature of the buildings, as in Freetown, in Sierra Leone.
Finally, Pierre Vanderstraeten insists on the need to ventilate cities. “You have to create wind corridors and offer a mesh to have prevailing winds that bring the most extensive natural ventilation possible”, he explains. The city of Stuttgart, Germany, has adapted in this way to allow the wind to come and cool the city. “Above all, you must not block its passage with constructions,” adds Pierre Vanderstraeten.
Bringing rivers back into the open air, rethinking public space to green it, brightening surfaces… The solutions exist and the public authorities seem to be aware of the need to counter these heat islands, as shown by the work that will begin this winter for demineralize and green Place Flagey in Ixelles, which was completely renovated some fifteen years ago.
Methodology We worked from the map of Brussels Environment cool islands, which takes “into account not only air temperature, but also exposure to solar radiation, wind and air humidity, which play a role in the stress felt due to heat. These maps are more adequate and more detailed than those integrating temperature only.” (source).
We used the free mapping software QGIS to extract the data and assign each statistical sector and each district of Brussels an RGB color (from red to blue depending on the intensity).
The intensities in % were defined thanks to a Python script, which was also used for the classification of the zones, from the hottest to the coolest, to facilitate the analysis.
Excel then made it possible to gather the data: to couple the geolocation of the statistical sectors (geojson) with the names of the streets/neighbourhoods/municipalities and the corresponding heat intensity, so that the reader can easily search the data and locate himself on a map of the Brussels Region. The map was drawn using Leaflet, a free JavaScript mapping library.
To simplify the narrative, the word “district” has been used instead of “statistical sector”.
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