Infrared image of city showing urban heat island

Urban Heat Islands Are Growing

Urban heat islands are growing in America, and we need to be aware.  As cities are sprawling out into the countryside these islands are growing.  An urban heat island is a metropolitan area that is significantly warmer than its surroundings.  According to the EPA, the annual mean air temperature of a city with one million people or more can be 1.8 to 5.4 degrees Fahrenheit warmer than surrounding areas.  The difference in temperatures is usually greater at night.  The difference is also greater in the winter than the summer.  We have seen a difference of 22 degrees between a city and a rural area during the evening.

How to Build an Island

Unlike the islands in a tropical destination, urban heat islands are man made.  Heat islands are created as vegetation in rural areas gets replaced by asphalt and concrete.  Asphalt and concreteGraph showing the temperature difference from rural to city of an urban heat island absorb the incoming solar radiation rather than reflect it.  This absorption causes the surface temperature to rise.  Other major contributions are tall buildings and narrow roads, that trap the heat near the surface.  As the areas surrounding a city cool more quickly, they form an island of heat.

Slowing the Growth Process

Urban heat islands can be slowed or reversed. The EPA lists five strategies that cities have begun implementing:
1.  Increasing tree and vegetation cover
2. Growing a vegetative layer on rooftops
3. Using roofing materials that reflect the sunlight and heat away from a building
4. Using pavement materials that remain cooler than traditional materials
5. Using smart growth in developing communities

Even with such a simple solution, most people are unaware that there is a problem.  Some things such as green roofs may not be possible when you live in a traditional home, but every member of a community can contribute to the fight.  We can plant trees around our homes or make sure we are using more energy efficient appliances.  We either look forward and accept the increased heat that is to come or we turn our focus to controlling it.

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