McIntire, Martell 1
Leva McIntire, Daniel Martell
PHY 4242 Atmospheric Science
Thermal Islands Team Assessment
May 19, 2010
Thermal Islands Assessment
Situation: Thermal Heat Islands (THIs) are the thermal effects observed around
urban areas around the globe. These pose a general health threat to urban
populations because during heat waves the heat is further amplified by the urban
setting causing an increase in morbidity and mortality. In addition, these have been
suspected to cause severe weather down the wind stream of larger cities. It is
therefore in the interest of communities to develop and practice mitigation policies
for the THI effect.
Scenario: It is our task to develop an ESS analysis about the effects of thermal heat
islands on the urban and suburban settings. Our goal is to identify what makes a
thermal heat island as intense as it is and suggest mitigation policies.
Group Understanding of Phenomena: We currently understand Thermal Heat
Islands (THIs) to be strongly correlated to a large condensed populous, large surface
areas covered in concrete and asphalt, and an increase in pollution in the urban
setting compared to rural areas. It is our consensus that the largest contributing
factor is the surface area covered in concrete and asphalt. Building materials such
as these absorb large amounts of heat during the day and release this heat during
the night resulting in higher night-time temperatures in urban areas and amplifying
heat waves within the city.
It is our understanding that the heat inversion caused by this also traps
pollutants within the urban setting and that these pollutants only enhance the effect
(positive feedback). Automobile exhaust, industrial emissions, and smoke are all
concentrated in cities and can act as greenhouse gasses trapping extra heat during
the day. Smog also poses a significant health risk on its own. In addition to this
pollution is the heat generating activities of the condensed populous. A
concentrated populous means more electronics, cars, and lights which increase
transformation of electrical energy to thermal energy and increase the temperature
in the urban setting.
Questions:
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Are thermal islands bad?
What are the main problems associated with thermal islands?
What people groups do thermal islands affect?
Is pollution a major contributor to thermal islands?
Would changing our building materials decrease the thermal
island effect?
Do cities create their own weather?
Do thermal islands contribute to weather patterns in/near the
city?
McIntire, Martell 2
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Will technology alone be significant enough to curb the negative
effects of thermal islands?
Are thermal islands solely a characteristic of major urban centers?
Are there natural thermal islands?
How long have people been studying thermal islands?
Do we believe that thermal islands are relatively recent
phenomena?
What are the thermal island characteristics of Seattle?
Does a thermal island exist in Seattle?
Are thermal islands seasonal?
What is the average temperature difference between the
city/country in the summer compared to the winter?
Can we model thermal islands in the lab?
Do atmospheric differences (air quality, particulates, etc.) between
the cities and rural environments significantly contribute to
thermal islands?
What are the main factors governing whether a thermal island
exists in a city?
Do all major cities have thermal islands associated with them?
Are the effects of thermal islands projected to increase in
intensity?
Are there any practical individual things that people can do to
decrease their thermal footprint?
Should cities enact new policies to curb thermal island expansion?
Should there be a thermal island footprint tax or offset like what
has been proposed for carbon?
Where are the properties of building materials that cause them to
act like positive feedback mechanism on thermal islands?
Would running water through a city help alleviate the thermal
island effect?
Does building insulation affect thermal islands?
What are the main problems associated with thermal islands?
The most direct problems that thermal islands pose to city dwellers are the
mortality and morbidity associated with excessive heat in the summer. Thermal
islands increase a cities temperature on an average of 1-3 degrees Celsius. Couple
this with the natural increase in temperature during the summer and occasional
heat waves this can pose a significant threat.
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(Image courtesy NASA/Goddard Space Flight Center Scientific Visualization Studio.)
What people groups do thermal islands affect?
Thermal islands tend to have the biggest impact upon the old, young, poor
and disabled that live in cities. These people groups are at highest risk during heat
waves and excessive heat events (EHEs). While the technology may be available to
mitigate the dangers of EHEs for most people these groups frequently do not have
sufficient access to stay safe.
Should cities enact new policies to curb thermal island expansion?
According to the literature provided there seems to be significant evidence
for green or lightly colored roofing to be effective at reducing the thermal heat
island effect over certain rooftops. If an entire city were to practice either of these
options in roofing then the specific urban area could significantly decrease their
thermal heat island effect. There are, however, two problems with this route. The
first is that the lighter colored roofing requires too much maintenance. The white
roofing, tested in the article “Beating the Heat in the World’s Big Cities,” required
regular cleaning and repainting in order to be effective, making this a less attractive
option for city dwellers. The second option is green roofing. This involves planting
on rooftops. While this seems to be very effective and low maintenance, many
contractors are not trained or ready to begin building green roofs.
http://earthobservatory.nasa.gov/Features/GreenRoof/
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Would running water through a city help alleviate the thermal island effect?
In the article “Beating the Heat in the World’s Big Cities,” the role of
vegetation in decreasing the thermal heat island effect is described as being
dependant on their ability to evaporate water (2). So it would seem that running
water through a city and thus increasing the amount of water would increase the
amount of water which would evaporate. So running water through a city does
seem like it would be helpful in lessening the thermal heat island effect.
However, looking at vegetation and thermal maps of Manhattan, it would
seem that the presence of water alone is not enough to reduce the thermal heat
island effect but that the vegetation is the major requirement for effect evaporating
of water and cooling of the urban environment.
(Map of Manhattan showing the vegetation density within the city. Image courtesy of NASA.)
http://earthobservatory.nasa.gov/Features/GreenRoof/
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Do thermal islands contribute to weather patterns in/near the city?
The simple answer is yes. The presence of a thermal island in an urban
center does contribute to a change in the weather that the city experiences. It has
been reported that regions downwind of a thermal island have a greater than
normal incidence of thunderstorms. This is most likely due to the extra heat lifting
moist, unstable air to a height where thunderstorms can develop.
(Image courtesy NASA: http://rsd.gsfc.nasa.gov/912/urban/profile.gif)
Are there any practical individual things that people can do to decrease their
thermal footprint?
Yes, being ecologically aware is a good place to begin reducing our thermal
footprints. Using less power, recycling, and cultivating an environmentally
responsible lifestyle will help mitigate thermal heat islands. Also, planting tress and
vegetation in your community, using reflective paint on your roof, and limiting the
amounts of pollutants we put into the atmosphere are other good ways to help
reduce the heat island effect.