Planting Trees to Reduce Summer Heat
There is no time like right now.
Record breaking heat is no longer rare. In just two short years since the unthinkable happened in British Columbia, when my neighboring community of Lytton burned to the ground in 2021, heat waves, wildfires, and the evacuation of cities are now regular occurrences in Canada and other parts of the world.
The thick smoke from Canadian wildfires blanketed the eastern half of North America this year. Suddenly the east was introduced to the “joys” of smoke forecasting and whether it was safe to be outside for long, something the west has dealt with since the uptick in large catastrophic fires starting around 2003.
The first week of July 2023 was the hottest in the history of the planet, with “history” referring to records dating back more than 120,000 years to a previous inter-glacial period. Over one third of the US lived under heat advisories this summer.
It feels depressing to think that there will only be more and more of this in our future. While air conditioning may become essential to survive a heat wave, the energy it uses and the limitations of energy grids could mean many people must survive without it. There are other more natural and less energy intensive strategies to consider, and that includes planting trees to reduce summer heat.
Strategically planted trees can reduce the temperatures we are struggling with and provide much needed natural relief from the stress of concrete and pavement found in cities and towns.
“The best time to plant a tree was 20 years ago. The second best time is now”
– Chinese proverb
How much cooler is it under a tree?
Trying to find an exact answer to the question of “how much cooler is it under a tree” is a challenge. I read everything from 2–9°F (1–5°C) based mostly on evapotranspiration (the way plants move water from the soil up through their stems and release it to the air through their leaves) up to 25°F cooler or more due to shading of surfaces below the trees.
What is the most interesting to me though, is that regardless of what the thermometer is reading, you experience cooling under a tree. There is a tangible difference in how you feel standing in the sun versus standing in the shade of a tree.
The combination of a shaded surface below you (which is cooler than a surface being heated by direct sun), the evapotranspiration of the tree which rises the humidity around you, and the shade above you created by the leafy canopy all contribute to what you experience in this cooling effect.
Tree canopies can block 30% or more of the solar radiation depending on how dense their leaves are. That’s why big-canopy broad-leaved trees like maples and oaks are highly prized for the shade they produce.
How do trees reduce heat?
Lets take a closer look at those main points from above, and think about ways to make trees work where you live.