Geoscience Reference
In-Depth Information
(b)
Figure 5.13 Urban heat island in Atlanta, Georgia.
(a) This image from September 2008 shows natural colors where dense urban
development is gray, bare ground brownish, and vegetation green. (b) A land surface temperature map from the same day where cooler
temperatures are yellow and hotter temperatures are red. Notice the distinct spatial relationship between the two images, with warmer
temperatures clearly associated with the dense urban areas.
to 50% of insolation. During the winter months, in contrast, a great
deal of sensible heat is generated through artificial heating activi-
ties. Humans also alter the heating characteristics of cities through
the production of pollutants such as ground-level ozone and other
aerosols. In general, about 10 times more human-produced par-
ticulates are present in urban environments than in rural areas. Al-
though these pollutants increase the reflectivity of the atmosphere
above cities, thus reducing insolation, they cause an increase in the
amount of infrared energy re-radiated downward to the surface.
An excellent example of an urban heat island is Atlanta, Geor-
gia. This southeastern city has grown rapidly since the middle of
the 20th century, becoming the leading commercial, industrial,
and transportation area of the region. During this time, Atlanta has
been one of the fastest-growing metropolitan areas in the United
States, with population increasing from about 2,300,000 in 1980
to a projected ~6,000,000 in 2015. Associated with this explosive
growth has been a dramatic expansion of the urban environment at
the expense of agricultural land and forest. As a result, the air qual-
ity of the Atlanta region has decreased significantly, with increased
amounts of ozone and volatile organic compounds polluting the
air. Another impact has been the well-defined urban heat island
that has evolved (Figure 5.13). As you examine this image, note
that May temperatures in the central business district reached 45°C
(113°F) in some areas, whereas they were as low as 22°C (71°F) in
the surrounding countryside. No wonder the city is called
Hotlanta
by many residents.
KEY CONCEPTS TO REMEMBER ABOUT
URBAN HEAT ISLAND EFFECT
1.
The urban heat island effect has a measureable impact on
local temperature patterns within cities. Cities tend to be
warmer than surrounding rural landscapes for a variety of
reasons related to land cover and energy consumption.
Temperature and Location
To explore temperature patterns in another way, go to the
Geo
Media Library
and select
Temperature and Location
. In this
animation you can “visit” five cities that experience the kinds of
seasonal temperature patterns discussed in this chapter. These
cities are Cordoba, Argentina; Yakutsk, Russia; Manaus, Brazil;
St. Louis, Missouri; and San Francisco, California. Visit each of
these cities during each season and access insolation and tem-
perature data from each location. As you work through this simu-
lation, note how the environmental factors we have discussed in-
fluence the seasonal range of temperature at these places. Once
you complete the simulation, be sure to answer the questions at
the end to test your understanding of this concept.
SUMMARY OF KEY CONCEPTS
1.
The atmosphere contains four major layers: the tropo-
sphere, stratosphere, mesosphere, and thermosphere.
the troposphere, which cools with increasing altitude at
a rate of 6.4°C per kilometer or 3.5°F per 1000 ft. This
