During the summer, and especially during heat waves, cities become real heat islands. Aware of the risks this poses to health, cities are thinking about how to transform their public spaces.
At the beginning of March, the city of Lausanne unveiled its vision for the future Place de la Riponne. Within a few years, this space could be transformed into a green area, covered with planted terraces, play areas, many trees and, above all, give "an important place to water".
"It's a beautiful step, a project that provides answers to the problems of this square and to current challenges, whether it be tree planting or the issue of the climate," said Grégoire Junod on the RTS airwaves.
If the project, designed by the firm Paysagestion SA, still has to be approved by the Municipal Council and overcome any oppositions, its orientation is fully in line with the new urban planning and architectural strategies designed to respond to the challenges of climate change.
During the summer, and more particularly during heatwaves, cities turn into real heat islands. This phenomenon typical of the urban climate denotes the difference in air temperature between the city, which is warmer, and its periphery, which is cooler. "In Switzerland, this difference can reach 6 degrees," says the Federal Office of Meteorology and Climatology MeteoSwiss.
"Heat islands have a significant health cost, with, for example, higher respiratory and cardiovascular risks that reduce life expectancy," explains one of the authors of a study published by the École polytechnique fédérale de Lausanne (EPFL).
This overheating of urban centers is all the more worrying because it has concrete effects on health. A year ago, the École polytechnique fédérale de Lausanne (EPFL) published a large study, providing a first assessment of the cost of heat islands on human health. "Our study shows that they are not only a comfort problem, but that they have a significant health cost, with, for example, higher respiratory and cardiovascular risks that reduce life expectancy," explains one of the study's authors, which covers 85 European cities, including Geneva.
For the City of Calvin alone, the study estimates that urban heat islands can lead to four additional heat-related deaths per 100,000 inhabitants per year. However, it also notes that these same heat islands help avoid 3.4 deaths due to cold.
To change the situation and prepare for heatwave periods expected to be more frequent and prolonged, cities are rethinking the transformation of their public spaces. Indeed, solutions exist to mitigate heat islands.
They include increasing the number of green and water spaces, creating cool-air corridors, installing green walls, building light-colored roofs with high reflectivity, promoting cooling construction materials like wood, and adapting street surfacing.
As part of its adaptation strategy to the new climatic realities, the city of Lausanne has just published a report devoted to the coverings of exterior surfaces. The Energy research institute of the University of Applied Sciences of Engineering and Architecture of Fribourg (HEIA-FR), in collaboration with the company Ecoscan SA, thus evaluated both "the carbon footprint of the coverings and sought to define the most relevant planning principles to combat the city's warming and improve its permeability."
Regarding overheating in urban environments, scientists modeled and tested various surfaces by integrating several parameters, while evaluating the additional effect of tree planting. Their conclusions highlight extensive materials, such as topsoil, grass-gravel, or natural stabilized material.
"Combining tree planting and judicious selection of surfaces — light, or with low thermal conductivity — is necessary to create islands of cool where possible. Implemented alone, these two solutions are insufficient to effectively cool the city," explain the authors of the study. Other criteria, such as material permeability or their local sourcing, are just as essential to achieve an optimized solution.
As more than half of the world's population now lives in cities, redesigning the urban landscape is a priority. "Combined with rampant urbanization, the urban heat island effect, due to human activities and constructions, could cause cities to warm twice as fast as the global average, which could lead to a temperature increase of 4 °C if greenhouse gas emissions remain on their current trajectory," one can read on the website of the United Nations Development Programme (UNDP).
"In Switzerland, we mainly make small, sporadic adaptations to increasing heat periods — here a few trees in a square, there a giant misting system, like in Zurich," explains William Fuhrer, professor at the Bern University of Applied Sciences.
This adaptation of city centers must be started without delay since it will take time. Take the simple solution of tree planting: for it to begin to bear fruit, it takes a good decade, according to a study carried out by a team from the Swiss Federal Institute of Aquatic Science and Technology (Eawag).
While Switzerland is not among the worst students in terms of urban planning, it still has a wide margin for maneuver, according to William Fuhrer. "In Switzerland, we mainly make small, sporadic adaptations to increasing heat periods — here a few trees in a square, there a giant misting system, like in Zurich. But nature requires more space to develop effectively. In reality, it would be necessary to let nature thrive in cities as much as possible," explains this professor at the Bern University of Applied Sciences.
According to UNDP experts, while the global urban population is expected to double again by 2050, cities already contribute significantly to global greenhouse gas (GHG) emissions. "That is why it is increasingly important to develop local climate plans in which cities commit to strengthening their climate resilience, increasing their adaptive capacity, reducing their emissions, improving their disaster preparedness, modernizing their response strategies and adopting stricter adaptation and mitigation measures."
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