Every tree counts – you can’t imagine how important trees are for weather in the cities

People love green cities. Trees seem to bring some nature into a somewhat cold and lifeless environment of the city. We know that they help us too – they provide us with shade, they host birds and some other small animals, they clean the air we are breathing. But a new study from University of British Columbia showed that even a single tree is extremely important and losing it will cost us money.

Trees reduce wind speed by a factor of two – you would notice a difference. Image credit: beglib via Wikimedia(CC BY-SA 3.0)

When cities are redoing streets, they tend to cut down old trees in efforts to make streets wider and sidewalks more convenient. It is all well and good, but city residents don’t really like it – they enjoy looking at trees in otherwise grey environment. However, none of us would think that losing a single tree can have a big impact on weather of the city. This new study revealed that losing a single tree can increase wind pressure on nearby buildings and drive up heating costs. Scientists found this out by studying computer models.

Researchers used remote-sensing laser technology to create a highly detailed computer model of a Vancouver neighbourhood. Scientists wanted to see how different scenarios affect wind formation in the area – what happens when trees are bare, when they have many leafs and what when trees are completely gone. Scientists found that removing all threes completely would increase the wind factor on pedestrians by a factor of two. This is a massive difference that cannot be overlooked – while walking in 15 km/h wind is pleasant, 30 km/h wind is already dangerous.

But it is not just pedestrians – tress help mitigating wind pressure on buildings, which is responsible for a large part of heat energy losses. Without threes energy consumption in a building can grow by as much as 10-15 %. Therefore trees are important, because even when bare they are reducing wind pressure on building by tremendous amounts. Marc Parlange, supervisor of the study, said: “Deciduous trees, which shed their leaves every year, reduce pressure loading on buildings throughout the year–it’s not only evergreens that are important in the city”.

Scientists say that researches like this can alter the way we look at weather forecasts. Temperature and wind will mean different things for people who live in streets rich with plants and those who live in areas with no trees. This information should also help city planners to make decisions about trees in streets – sometimes changing plans to protect a single tree may be a smart move.


Source: University of British Columbia

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