Monday, August 8

Santiago studies the use of grass in paving to control temperature and influence the urban climate

The architect of the Santiago Consortium, Ángel Panero, was walking along Praza do Obradoiro in Santiago de Compostela during confinement when he noticed something that had not been there before. The absence of tourists and citizens had encouraged nature to show itself without limits and weeds and moss sprouted between the stones. “The vision was almost that of a prairie,” summarizes Panero in a conversation with An investigation was born from that image, in which the Biodiversity Analysis and Conservation Group of the University of Santiago (USC) participates and which has yielded a surprising discovery: the plants that grow in the joints between slabs manage to reduce up to 25 degrees soil temperature.

An investigation was born that aims to answer a transcendental question in these times of climate change and heat waves: is it possible to lower the temperature of a city with small plants? The first results are promising.

Miguel Serrano is a professor in the Department of Botany at the University of Compostela. In a telephone conversation with this newsroom, he explains that the first commission that the Consortium made them was limited to the elaboration of a catalog of plants present in the stones of Santiago. The technicians of the Consortium wanted to know if pulling the grass between the stones during the cleaning processes was the most correct or if these vegetables could offer some advantages in the management of water, CO2 and oxygen. The Santiago Consortium is a body participated by the city council, the Xunta and the central government and one of its functions is to protect the rehabilitation and conservation of the monumental center of the Galician capital and the treasures it hides. Its technicians have been taking care of the city’s soil for more than a decade within the framework of the “The ground you step on” program.

The big surprise

What they didn’t know at the Santiago Consortium was that university researchers were about to make a big discovery. By means of a thermographic camera they obtained proof that plants alter the temperature of the stone on which they settle. Professor Miguel Serrano sums it up this way: “We decided to use the camera to see what we found. The bare pavement marked temperatures of 55 degrees and the surprise was to see that where there were very small plants we established differences of 25 degrees with records of just 30 degrees in the sun”.

The small spaces of green between the stones may seem insufficient to change things but they are not. “You have to think there are 60,000 square tiles inside the historic center. If we join all the joints that separate the stones, we are still talking about a green soccer field in the middle of the city. It is not negligible”, says the architect Ángel Panero.

Professor Miguel Serrano is also excited about the possibilities that the temperature changes generated by plants in the soil can be perceived higher up, where we humans breathe: “Obviously there has to be some effect that can be detected by humans. To what level and in what magnitude is something that we have to test later.

Encouraged by the surprise that the first thermography produced, Serrano published a tweet with the finding that soon became viral among the scientific community: “The Germans retweeted it and the English sent it to the mayor of London. He has been quite successful.” Along the same lines, Panero assures: “I don’t know any city that is working on something apparently as inconsequential as stone joints, but everyone is doing things about the importance of green for the health of citizens. This is perfectly exportable to the whole world”.

lumpen plants

The scientific names of some of the plants that affect the temperature of the stone are the following: Sagina procumbens, Plantago coronopus, Poa infirma, Oxalis corniculata. Professor Serrano assures that these species have always been considered as “lumpen plants”, whose value was ignored and that, almost always, they were condemned to disappear, uprooted by the cleaning services of the cities. One of the characteristics of these plants is that they do not require water under their roots and they manage to live in very extreme circumstances and even withstand vehicle traffic or the footsteps of neighbors and pilgrims. Researchers Patricia Sanmartín, Jesús Aboal and Sabela Balboa work in Serrano’s team to study them.

The project promoted in Santiago proposes a change in the aesthetic paradigm and a reflection on the need to dispense with excessively clean stone in historic centres. Those who, until recently, struggled daily to polish the city now value another path: incorporating the urban microgreen as part of the landscape. Ángel Panero is one of them: “Green is associated with life and the well-being of human beings. This is what has motivated us to work on an idea to which we give importance because the times we are living in are teaching us that small things are very beautiful”.

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