A number of my friends decided to visit the beautiful island of Hawaii this month. Daydreaming about spending time on the beach or hiking Oahu’s “Stairway to Heaven” made me think about a different kind of island: The Urban Heat Island. Urban heat islands aren’t literal islands, though. Certain cities are referred to as urban heat islands because metropolitan temperatures tend to be higher (as much as 3 degrees Celsius annually) than local rural areas. Madison, Wisconsin is no exception to this concept.
“The growing season in Madison lasts around five days longer than in surrounding rural areas, meaning the meteorological conditions that contribute to trees leafing out and gardens growing last a little longer in the city. Moreover, the heat island effect can protect a city against late spring and early fall freezes, and often keeps urban nighttime temperatures above freezing on nights when rural areas experience mild freezes” – UW-Madison Water Sustainability and Climate
Rankings of the hottest “heat islands” vary depending on who you ask. In spite of this, heat islands follow a certain formula. Cement, dark roofs, air pollution, and the absence of vegetation all contribute to high heat in urban areas. Although tamer winters sounds like a desirable side effect of heat islands, the negative impacts include lower air quality and higher incidence of heat related illnesses such as heat stroke.
Concrete roads and dark shingles store up heat and lead to higher temperatures at nighttime. Not only this, but also dark surfaces can heat up runoff exceptionally well which ends up warming the surrounding water. Both people AND aquatic life suffer from high heat. It’s no surprise that the Environmental Protection Agency has addressed this issue and assembled solutions for the general public to cope with the problem.
Vegetation has the ability to reduce air temperature through evapotranspiration. Like a fan over water, trees and plants release water as moisture which ultimately brings down surface temperature. The fact that plants are brighter in color help as well. Green and white roofs (mentioned in a previous post) help block out heat from the sun.
An article on National Geographic also pointed to people- yes, you and me- as heat emitters. Even the most energy-efficient “sustainable cities” are going to have human heat signatures. But have no fear! Ample vegetation and thoughtful city planning are simple ways to curb the heat island issue. Of course, the complication of other factors like runoff and thermal insulation requires a more exhaustive solution.
Do you live in a populated area? Or is your town further removed? Have you ever noticed a difference in temperature between landscapes? Let me know in the comments!