HS Environment Research: Trees cool European cities, street tree can sequester even more carbon than growing in the woods

In the cities of Central and Northern Europe, the temperature difference between the trees growing and the rest of the urban environment was as high as 8–12 degrees.

City trees cool urban areas at multiple temperatures, reveals a recent study from the ETH University of Zurich.

According to it, the surface temperature in urban areas growing trees was on average 2–4 degrees lower than in the lush green areas of cities.

The difference in temperatures was even greater when comparing the areas growing trees to the built environment outside the green areas. In this comparison, the difference in surface temperatures could be as much as 12 degrees.

The study was published by Nature Communications newsletter.

Measured the differences were greatest in the cities of central and northern europe, where the temperature difference between the trees growing and the rest of the urban environment was 8–12 degrees. The largest differences were measured in Slovenia, Austria and Germany.

The study involved 293 cities across Europe. There were five cities in Finland where the temperature differences between the trees growing and the rest of the urban environment were 8–10 degrees.

In contrast, in the southern parts of Europe, the cooling effect of trees was lower, at only 0–2 degrees. The smallest differences are found in Malta, Cyprus and Greece.

Wood cool the environment in three ways. They evaporate the water, which cools the air. The leaves of the trees also reflect the sun’s rays back into space.

Of course, the trees also shade. However, the shadows move and change over the course of the day, so they cool the environment unevenly. In this study the effect of shadows was ignored.

The measured temperature differences are therefore based only on the cooling caused by the evaporation and reflection of the trees.

This may also explain why the cooling effect of trees was less in southern Europe. When the air gets too hot, the trees close their air gaps and evaporate less to prevent them from drying out.

From France, the study involved several cities that were not specifically named. The picture is from Paris.

Investigator Jonas Schwaabin the study led by cities looked at both satellite measurements and ground-based measurements. The researchers also calculated temperature differences between urban, forest, and rural areas.

The material collected was exceptionally extensive. On the other hand, its resolution remained rather rough. In reality, temperatures can vary by meter. Now this was overlooked in the study.

City trees Assistant Professor of Applied Urban Meteorology Leena Järvi The University of Helsinki also points out that the study explicitly looked at surface temperatures.

“Measured from the surface of the earth, the differences are usually greatest,” says Järvi.

If you think about the comfort of the park from the point of view of people, the most meaningful thing is to look at the air temperature at a height of a few meters.

“At that altitude, the temperature differences between urban areas are usually already a few degrees smaller.”

Correspondingly, the differences shrink even smaller if temperatures are measured from a higher atmosphere.

Lake according to recent research, its methods are still interesting. There was really nothing surprising about him in the results.

The benefits of street trees not only in cooling the air but also in the binding of small particles has been known in the past.

In addition, trees sequester carbon dioxide. In an urban environment, a tree growing alone can even sequester more carbon than a tree growing in a forest that fights its habitat with other plants.

“When designing new urban areas, more and more attention is also being paid to temperature control. Trees offer one excellent alternative, ”says Järvi.

Street trees that is, in addition to green infrastructure, another viable way to cool the urban environment is blue infrastructure, or so-called water elements such as pools, fountains and canals.

As the water in the pools evaporates, it cools its surroundings. The temperature difference between the surface and the air also causes the air to move.

Read more: Trees should be planted in street shafts of different lengths as it could curb harmful small particles

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