Ron Wilson

Ron Wilson

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Just One Tree

Just one tree makes a difference

This screen shot of a computer visualization shows how wind moves through a neighborhood in Vancouver, Canada. When trees are lost, wind pressure on nearby buildings rises and so do heating costs as a result. Credit: University of British Columbia

Just one tree in the right location makes a difference. A single urban tree can moderate wind speeds, keeping pedestrians comfortable as they walk down the street, according to a new University of British Columbia (UBC) study. Losing a single tree can increase wind pressure on nearby buildings and drive up heating costs.

Using remote-sensing laser technology, the researchers created a detailed computer model of a Vancouver neighborhood, including every tree, plant and building. They then used computer simulation to determine how different scenarios - no trees, bare trees and trees in full leaf - affect airflow and heat patterns around individual streets and houses.

"We found that removing all trees can increase wind speed by a factor of two, which would make a noticeable difference to someone walking down the street. For example, a 15-km/h (9-mph) wind speed is pleasant, whereas walking in 30-km/h (18-mph) wind is more challenging," said lead author Marco Giometto, who wrote the paper as a postdoctoral fellow in civil engineering at UBC.

Trees also moderated the impact of wind pressure on buildings, particularly when it goes through small gaps in and between buildings.

"Wind pressure is responsible for as much as a third of a building's energy consumption. Using our model, we found that removing all the trees around buildings drove up the building's energy consumption by as much as 10% in winter and 15% in summer," Marco said.

The researchers compared the simulated scenarios against a decade of measured wind data from a 30-m (98-ft.) research tower in the same neighborhood. They discovered that even bare trees in the winter months can moderate airflow and wind pressure, contributing to a more comfortable environment.

"Even bare branches play a role. 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," said Dr. Marc Parlange, Civil Engineering.

"Information from such models can improve weather forecasts in order to predict the effects of a storm on a building and pedestrian level," said Dr. Andreas Christen, Geography. "It could also help city planners in designing buildings, streets and city blocks to maximize people's comfort and limit wind speed to reduce energy loss."—from a University of British Columbia press release “Trees can make or break city weather.”

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