Summer is almost here. Summer means vacation and a chance to beat the heat in the city. Perhaps we head out to the beach, the mountains or a walk in the woods. Somewhere cooler. When we picture comfortable summer temperatures, we seldom think of heading into the city, unless our destination is a climate controlled movie theater, shopping mall or office building. Why are cities so hot?
The building blocks of the city – steel, asphalt, concrete, glass and brick- have high absorptivity, which is a measurement of how strongly a chemical species absorbs light. When the sun beats down on these solid materials, they absorb and store heat from the sun. In contrast, green vegetation has low absorptivity, reflecting much of the solar radiation back to the sky. Lower absorption means lower stored heat.
When the sun goes down, the dense building blocks of the city release their stored heat, keeping the city hot well into the night. Tall buildings prevent the radiating heat from escaping into the night sky. Consequently urban settings have two disadvantages to cooling: trapped heat in the building blocks and poor air circulation. It’s not unusual for cities to be 10-15 degrees warmer than the surrounding countryside on hot summer nights.
“Urban Heat Island” is a term used to describe these city areas that trap heat. The magnified heat triggers an increased demand for electricity for cooling which increases greenhouse gas production. As you might imagine, the heat and smog contributes to a number of heat related ailments such as heat cramps, exhaustion and heat stroke or simply the discomfort walking to your car across a sea of pavement.
So when you pack the car to escape the heat, nod appreciatively at your trees and garden plants who stay behind and help to cool your property. And if you want to strategically plant trees to aid in cooling your house – we are the right folks to help.