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Due to climate change, heat in cities and villages has become an increasing problem. Is there anything to do about it? Yes: tiles outward, green inward. But it’s the tall trees that make the difference, and they don’t grow in a day.
Ruim 10 procent van Nederland bestaat uit steden, dorpen en industrieterreinen. Welke rol spelen die in natuurherstel? NU.nl zoekt het uit in een serie over welzijn, klimaat en biodiversiteit bij jou in de straat. Deel 1: hitte.
En ontvang een bericht bij een nieuw deel in deze serie
Do you live in a big city? Then there’s a good chance you’ll be doing your shopping on foot. But do you choose the left or right sidewalk? Research shows that people often take a sunny road on their way to the supermarket. When returning with a heavy bag of groceries, people tend to seek shade more often.
It’s a small example of the new climate challenge facing urban designers: the demand for shade is on the rise.
This is now becoming more widely recognized. The Nature Restoration Act, which the European Union will take over after the summer, calls for special attention to be paid to the greening of cities. And by 2050, at least 10 percent of the city’s surface should be covered with trees.
Trees improve air quality and provide opportunities for normal life. But trees provide cooling, too. This is no less important for Brussels.
Almere and Breda have temperatures up to 7 degrees warmer in summer
Therefore, heat in cities is a growing concern. The highest temperatures during heat waves rise twice as fast as the average summer temperature. The cities then get much hotter than the outer area.
There are several reasons for this, says KNMI. Pavement surfaces heat up faster and tall buildings reflect sunlight downwards. For example, more heat is “trapped” during the day in cities.
Cities also cool less well because less water evaporates. Lack of vegetation is a problem here, among others.
Results? A village of 10,000 people can be up to 4 degrees warmer than the surrounding countryside during hot summer nights. According to KNMI, the city of 200,000 residents has a maximum temperature difference of 7 degrees.
Trees make a big difference from one street to the next
But those are the averages. What about neighborhood to neighborhood, street to street, or even house to house? A few years ago, researcher Wibke Klemm decided to cycle through Utrecht with a cargo bike full of measuring equipment.
This allowed her to measure the radiation temperature of the pavement and facades. And that says something about how hot the street can get in a single day.
Klemm, who earned his Ph.D. through research at Wageningen University & Research, discovered that cities are actually made up of a mosaic of microclimates. In the streets with green front gardens and small trees, the radiation temperature was found to be two degrees lower compared to the streets without gardens and trees.
In streets where trees grew taller and wider, the cooling effect was twice as strong. In Utrecht, these streets were 4 degrees cooler in summer than fully paved streets.
The elderly prefer to sit in the shade in the afternoon
The parks are also cooler in the summer than the built-up city center. These parks are important to people’s well-being, according to Klemm’s research. I approached people and asked them where they like to sit, for example.
“In the past, the idea was that people in the garden mainly wanted to sit in the sun on hot summer days,” says Klemm. “That thinking has changed.” Preferences seem to depend on the season, time of day, and age.
Clem says that people make both conscious and unconscious choices in this regard. “Old people know where there are shaded benches.” They also often move with the day. “In the morning they can choose a seat in the sun, in the afternoon and in the evening.”
The trees needed to cool us in 2050 must be planted now
This growing need for shade seating requires something from designers of public spaces. First, it is important to properly protect existing trees in urban areas, says Klemm, who is currently the policy advisor for a sustainable living environment in The Hague municipality.
“The heatwaves are already increasing and it’s already 40 degrees in the Netherlands. So the trees need to be given good places to grow with not too much paving, so that the rainwater can penetrate the soil and reach the roots.”
To combat the heatwaves of 2050, it’s also important to plant more trees now. Tall trees are what mainly cool cities, and trees take decades to reach maturity.
But what are the types of trees? We will look at this in the continuation of the series, as we explore how cities and towns can contribute to restoring biodiversity. Veil tip: Remove the often planted plane tree from the list. Instead, choose a mix of native trees, preferably from one of the last wild populations in the Netherlands.
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