Once again, we’re facing weeks of sweltering heat during summer’s “dog days.” While we hope for an occasional rainy and cool reprieve, mostly we know we’re in for hot weather, and lots of sun, so most of us will look for a shady spot.

True Texans know that when chatting with a friend we move into the shade rather than stand in the sun. We park our cars in the shade when possible to avoid being baked alive when we return. We walk dogs on the shady side of the street rather than on fiery pavement that risks damage to their paws. You might find a 20 degree to 35 degree difference between a hard surface in direct sunlight and one shaded by a tree canopy.

Both trees and buildings provide cooling areas due to their shade, but trees are better. So what makes the difference? Tree-covered areas create their own little microclimate.

Trees don’t reflect heat back at you like buildings do. Buildings store and radiate heat into the surrounding area. Sidewalks and streets do that as well, so not only do their surfaces become hotter, the air above them does too. This stored heat may be radiated for hours. This difference can extend beyond the immediate area; a recent study in Washington D.C. found a temperature range of 15 degrees (85.4 Fahrenheit to 101.9 F) from the shadiest parts of the district to the least shady locales.

Trees also provide a special “cool island” effect under their canopies. This is due to water leaving their leaves through evaporation and transpiration. This cools surrounding air as the moisture becomes water vapor and drops toward the ground.

On a practical note, tree shade can save us money. Room temperatures in a shaded house can be 20 degrees lower than one in direct sunlight. This can significantly reduce the need for air conditioning during our hottest weather, thus lowering utility bills. Shading west walls provides the best cost savings. City budgets (your tax money) can benefit from shaded pavement. Streets in direct sunlight can heat to temperatures that speed their deterioration and need for repair, so more shade means more time before repaving.

Of course there are many other benefits derived from trees, things like oxygen, improved air quality, food and habitat for animals. Recent reports have suggested tree planting as the easiest way to slow climate change and improve the well-being of residents.

The bigger the tree, the bigger the shade. So the first takeaway here is to care for the trees you already have: water them in excessively dry weather, prune them cautiously, avoid disturbing the earth in their large root zone, and seek advice from an arborist when you have questions.

The second is to plant more trees. At last estimate, Galveston had around 50,000 residents. Just think, if everyone in Galveston planted just one tree this year, we would instantly have 50,000 more. Fall will bring perfect planting time, so let’s do it.

“Tree Stories” is an ongoing series of articles about island trees, tree care, and tree issues. If you have or know of a special tree on Galveston Island that should be highlighted, email treesforgalveston@gmail.com. Margaret Canavan is a Galveston resident, a Galveston County Master Gardener, and a member of the Galveston Island Tree Conservancy Board.


(2) comments

Bailey Jones

I think I may take your advice. Our yard is tiny, but I have a spot that could hold a decent sized tree. Something to block the evening sun from our porch would be a blessing. What sort of tree does well on the island?

James Lippert

Great advice! Given the same advice by my parents, have been actively planting & maintaining trees for decades in Galveston County.

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