Check the weather for your area on any given day and you’ll notice that temperatures are higher in the city than in the suburbs. That’s because cities tend to be hotter than surrounding rural areas by 5-7 degrees on average. And, believe it or not, some cities have recorded temperatures 20-25 degrees hotter during high heat events.
There are a number of reasons for this phenomenon known as urban heat islands: human activity, lack of vegetation, and building material choices. In the US, the top 3 cities with the greatest contrast in downtown temperatures vs. rural temperatures include Las Vegas, Albuquerque, and Denver. There is such a high concentration of dark impermeable surfaces, asphalt and concrete for example, that it causes heat to become trapped resulting in much higher urban temperatures. As sunlight hits these surfaces, it either gets absorbed into the building as heat, or it gets blown off into the surrounding communities.
City roofs tend to be flat and very hot in the warmer months. In fact about 25%, or 1 in 4 city square feet, is roof top. That is a huge area of square footage where better technology and cool roofing materials could make a great impact on excess urban heat. Cool roofing could help us achieve better sustainability in urban areas and, where it has already been implemented, these changes have proven to lower average city temperatures annual, especially during high heat events.
The Greeks were onto something when they chose white to adorn their iconic Mediterranean island homes . The reflective color choice wasn’t simply aesthetic; it was a wise choice for keeping structures cool amid the sweltering heat and sunlight of the Greek Isles. Perhaps if more buildings in urban areas adopted this centuries-old, cool roof convention we could begin to mitigate excess urban heat and improve overall urban health.