The power of greenery in an urban environment is more than just a visual aesthetic. The principle is simple: a tree you plant in autumn will eventually provide you with coolness in summer. The months of October and November were therefore dedicated to tree planting by many nature organisations and companies. For good reason our "Bomen zijn cool" (transl. Trees are cool) project, in which we measure the cooling effects of trees, was in its final sprint. So what did that measurement campaign actually look like? And can we already draw conclusions around the importance of trees?

Why is such a measurement campaign so important?

In hot summers, abundant paving in urban areas contributes to heat stress. At the same time, this paving causes waterlogging or flooding during heavy rainfall. So both heat and water literally have nowhere to go. By taking climate-adaptive measures and greening the environment, city temperatures can be lowered and water retention improved.

The cooling and comfortable effect of a tree is something almost all of us seek out during the summer months. Be it in our garden, a nearby park or a natural area. But just how big is the temperature difference between a paved environment and a tree-rich area? "With the citizen participation project 'Bomen zijn cool', supported by the City of Antwerp's climate fund, we can quantify the impact through effective measurements at various locations. To measure is to know, and with such substantiated evidence we can back up our experience and communication with research and conclusions," said Patrick Verdonck, Project Manager at Antea Group and one of the ambassadors of the 'Bomen zijn cool' project.

How did we go about it?

A critical aspect of our study included continuous measurements in the participants' gardens. Those measurements were made via sensors from Antwerp University, which the participants placed both in the trees of their gardens and on the front facade of their houses. Those sensors were used to measure and store the temperature. We also placed some reference points on the Groenplaats and in a sideroad of the Grote Markt, two locations with little greenery today.

Every two months, all these sensors were digitally logged by our ambassador participants and the results were passed on to Antwerp University for validation. Together with our scientific partner UA, we processed this data into interpretable graphs, clear figures and a handy digital platform. That dashboard can be consulted by participants and will be finalised for a wider audience in 2024. "The first figures and graphs clearly indicate that trees in the garden really do make a difference in terms of cooling," says Karl Clement, Antea Group's Project Leader.

Process of cooperation with participants

Our journey began with an informative evening at Ecohuis, where we shared the importance of our measurement research with all participants and ambassadors of the citizen participation project. This collaboration with a total of 53 participants was pivotal and led to a strengthened connection in the neighbourhoods, where participants not only played a role in the process, but also became ambassadors. We worked closely with our project team to compile essential information about the project on the UA website, where an infohub was also available for questions and comments from participants. This process provided valuable insights and strengthened the accuracy of our research.

What do we expect from the research?

Although the study includes only a small sample in one city, it does indicate the added value of trees in our cities. As such, we initially hope that our methodology will be used for more extensive research on heat stress in multiple cities. We therefore see the results of the study as a starting point, and not an end point. In addition, we naturally hope that the project will inspire and encourage citizens to plant more trees in their private gardens to bring cooling into the city.