Growing cities are the quickest changing environments on Earth. They impact local and regional climates, including temperature averages and extremes. These areas can alter temperatures by 2-5°F per 100 years and up to 20°F at night. These changes can affect your health, comfort, energy costs, air quality and visibility levels. Water availability, ecological services, recreation and overall quality of life can be affected as well.
The urban effect is due to changes in the thermal properties. If you look over the Phoenix area with an infrared camera, you’ll see areas like Sky Harbor Airport, highways and downtown areas remain much hotter than areas surrounded by water and plant life. Even the Peak of South Mountain is one of the hottest areas of the Valley. As the mountain gets higher, more and more rocks appear.
At a given time of day, a balance of incoming energy from the sun and outgoing heat from the surface determines the surface temperature. Solar radiation strikes the surface, and reflects a portion back to space and with the remainder both heating the surface and evaporating any water that may be present. Cement and rocks will holds the heat from the day and then releases it very slowly overnight. That’s why our nighttime temperatures are getting hotter every year. As our city continues to grow, the urban heat island will grow as well. These areas have the potential of being 10°F (6°C) higher than the surrounding areas.
