let grass grow between your sidewalks

  • 10

We call it “cities” because “concrete jungles that multiply the heat until it becomes hell” is long overdue. But it is so. Spanish cities seem specifically designed to favor all the dynamics and physical phenomena that help increase ambient heat. And we have it so normalized that we don’t even realize it .

For this reason, initiatives such as the one in Santiago de Compostela studying “the use of grass in paving to control temperature and influence the urban climate” surprise us. And they shouldn’t: we should talk about it a lot more.

What is a plant like you doing in a square like this? The story begins during the lockdown. Ángel Panero, an architect from the Santiago Consortium, realized that the Plaza del Obradoiro was full of little plants growing in the joints of the cobblestones of stone. He spent a few days thinking about it and decided to ask the Biodiversity Analysis and Conservation Laboratory of the University of Santiago about whether this vegetation could have a “refrigerating” effect on the soil (in the same way that it could have it in the field or in the parks).

Researchers from the University and technicians from the Consortium carried out several measurements to see to what extent these “weeds” were capable of lowering the temperature. And the answer is very curious: the plants that grow in the joints between slabs manage to reduce the temperature of the soil by up to 25 degrees.

It’s a surprise? Strictly speaking, no, it is not. As the climatologist Andreu Escrivà said, “the greater the coverage of urban vegetation, the lower the temperature, let’s talk about monumental trees or tiny weeds”. And this is something well studied and established: what happens is that at certain levels it can be counterintuitive.

If the question is "when does the heat wave end" the answer is: we have bad news

Do trees really get cold? In principle, “trees can help provide cooling in two ways: by providing shade and through a process known as evapotranspiration.” In general, the sensation of wind chill depends more on the ratio of electromagnetic radiation that we emit and absorb from our environment than on other things. In that sense“A tree’s canopy acts like a sunshade, blocking up to 90% of solar radiation, and increasing the amount of heat we lose around us by cooling the ground below us.”

The evapotranspiration, meanwhile, “occurs when the sun’s rays hit the canopy of trees, causing water to evaporate from the leaves.” And this, like the sweating systems of animals, cools the surface of the trees (something that ends up moving to the nearby local environment, no matter how big it is). The end result is that areas with vegetation can reduce the thermal sensation between 7 and 15 degrees, depending on the latitude where we are.

Against the concrete jungles. Actually, this is all about a reminder. We tend to forget the fact that our cities (and specifically Spanish cities) are concrete jungles that multiply heat. We have been talking about the “Iberian oven” for months (that is, all those factors that make the peninsula a “heat factory” in summer); Well, let’s keep in mind that in cities there can be up to seven degrees higher than in the surrounding countryside.

And, in many ways, the challenge is for public bodies and society itself to accept this and integrate it into their day-to-day activities. It’s not easy change the first impression (“it’s dirty”, “neglected”) and commit to ways of managing public vegetation that take advantage of its full potential: but in a situation like the current one, it may be the best investment.

Image: Jeremy Bezanger

We call it “cities” because “concrete jungles that multiply the heat until it becomes hell” is long overdue. But it…

We call it “cities” because “concrete jungles that multiply the heat until it becomes hell” is long overdue. But it…

Leave a Reply

Your email address will not be published.