Over the course of two years I filed approximately 200 books from our natural science library 756 times, but I also had the opportunity to talk with Tempe and Phoenix locals about local environmental issues on a regular basis. When this occurred, the discussion revolved around something called the ‘Urban Heat Island.’
What is the Urban Heat Island?
It is an effect created by the replacement of soil and Earth with concrete, tar, and other paved surfaces. These materials breath and absorb less than naturally occurring ground cover. When sunlight hits these pavements (especially dark or black ones) it is absorbed efficiently and released slowly. The effect is greatest at night, when cities cool slower than surrounding areas.
In many places, the Urban Heat Island effect is minimal, but in Phoenix it has caused average nighttime low temperatures to increase by 8ºF over the last 30 years! In Los Angeles, the average temperature is 6-7ºF higher. There, the probability of smog increases by 3% with every degree F (5% with every degree C) of temperature rise.
Smog traps heat too, which adds to the demand for A/C, which creates emissions, which traps more heat locally.. you get the idea, it’s a cycle of trouble. Find out about the problem where you live here.
Simply, an Urban Heat Island describes
greater heat accumulation over paved, city-based land.
When presenting our related research, I would explain all of the above then get out an infrared gun. Usually, I was speaking to a group with at least one kiddo, so they would get to do the measurements. We would point the gun at grass and concrete to measure temperature differences. The results were drastic.
Doing the experiment continually has caused me to never look at a sidewalk the same again. Take a look at some of these photos to see the Urban Heat Island effect in action.
Anyhow, once the heat is inside these heat-absorbent materials, it is difficult to get out. Hence the example of nighttime lows that I mentioned earlier. Even once the sun has set, the heat it leaves behind remains trapped inside our city streets. As a result, local residents receive less relief from the heat during the night (among many other problems related to heat). Benedicte Dousset, a scientist from the University of Hawaii performed a study providing evidence that Urban Heat Islands are a danger to people, especially at night.
From a NASA Feature Story, 12/13/2010:
[During the 2003 heat wave in Paris,] the risk of death was highest at night in areas where land surface temperatures were highest, she found. Buildings and other infrastructure absorb sensible heat during the day and reradiate it throughout the night, but the cooling effect of evaporation is absent in cities. The lack of relief, particularly among the elderly population, can be deadly, she explained.
Ramped up air conditioning usage may have even exacerbated the problem, other data presented at the meeting suggests. Cecile de Munck, of the French Centre for Meteorological Research of Meteo-France, conducted a series of modeling experiments that show excess heat expelled onto the streets because of increased air conditioner usage during heat waves can elevate outside street temperatures significantly.
Yet, there is a simple solution: Plant more trees to shade paved land
Shade does the trick and using a tree adds the benefit of air purification and beauty. Green roofs and painting surfaces white or reflective also help with the problem. Adding any of these renovations to or around a home will drop energy costs, which is true whether or not an Urban Heat Island effect is present. Adding a solar panel does even more, it shades the roof and turns all that absorbed sunlight into electricity! Be warned if you’re considering renovations: Adding grass may reduce heat, but will require more water! The trade-off will cause more problems than it solves.
Lesson plans from the ‘Ecology Explorers’
If you’re interested in reading the classroom structured lesson plan you can find it here.
Find out more about your city
If you would like to know what cities around the United States are doing to solve problems related to Urban Heat Island effects, visit this link and click on your city or region.
- City Temps May Soar From Urbanization, Global Warming (climatecentral.org)
- Climatologist: Urban Heat Islands Could Increase Mortality Rates (houston.cbslocal.com)
- Maximum Temperatures Plunging In The US For More Than 80 Years (stevengoddard.wordpress.com)
- Ghost town microclimates (infocult.typepad.com)
- In Focus: Cool Roofs (solarfeeds.com)