Having living in Chinse cities for two decades, I have been used to the urban heat island since when I did not even realize it. Cities are warmer than the surrounding countryside. When you live in the city, you probably don’t even realize that just a few miles away, the temperature is probably 5 degrees or so cooler.
Cities absorb more of the heat of the sun than the surrounding areas and, as a result, retain that heat for longer. Of course this starts a nasty loop of a warmer city requiring more air conditioning, which is more inefficient because the city itself is just so hot. Asphalt is a double-edged sword on the best of days. It’s not good for the environment to begin with, and once it’s there, it stabs us again by absorbing too much heat from the sun. So most of us are all in the same sinking boat of oil dependence together on one front. Basically we are trapped in an oven, which is our own homes. So how do we get out of it?
Solutions to the problems are relatively simple. Asphalt is naturally a very dark colour, giving it a very low Albedo (reflection coefficient) so instead of reflecting light (which includes energy in the infrared spectrum) it absorbs it instead. In an ideal world, you’d have a patch of grass on your roof instead of asphalt, and we call that choice the green roof movement. With this, people create an ecosystem on their roof so they can avoid the heat caused by the darker surface area, which also allows them to absorb water more efficiently to avoid some of the toxic runoff from their asphalt roof systems. It’s a good choice and usually it’s done with large roof systems on bigger buildings. At the more practical level for most of us is the move to much lighter coloured roofs or replacing asphalt altogether and going to recycled aluminium roof systems instead.
Urban Climate Lab, Georgia Institute of Technology, viewed 28 May 2015, <http://www.urbanclimate.gatech.edu/>
Jamison, 2012, ‘Urban Heat Islands: What Are They, and What Can You Do About Them?’, viewed 28 May 2015, <http://thegreenists.com/its-complicated/urban-heat-islands-what-are-they-and-what-can-you-do-about-them-2/10771>
Debra Miller, 2011, ‘Crazy In Alabama…But Reaping the Energy Savings of A Light Colored Roof’, viewed 28 May 2015, <http://www.greenspirationhome.com/crazy-in-alabama-but-reaping-the-energy-savings-of-a-light-colored-roof/>