Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Urban Heat Islands
Objective:
 Students will explain the urban heat island
 Students will identify trends or patterns by analyzing graphs and
images based on urban heat islands of New York City
 Students will understand the relationship between urban environment
albedo and urban heat island
Background Information:
An urban heat island (UHI) is a metropolitan area, which is
significantly warmer than its surroundings. According to the EPA, many U.S.
cities have air temperatures up to 10°F (5.6°C) warmer than the
surrounding natural land cover. This temperature difference usually is larger
at night than during the day and larger in winter than in summer, and is
most apparent when winds are weak. The main causes are changes in the
land surface by urban development along with waste heat generated by
energy use. As population centers grow, they tend to change greater areas
of land, which then undergo a corresponding increase in average
temperature.
How Do Heat Islands Form?
Heat islands form as vegetation is replaced by asphalt and concrete for
roads, buildings, and other structures necessary to accommodate growing
populations. These surfaces absorb—rather than reflect—the sun's heat,
causing surface temperatures and overall ambient temperatures to rise.
Displacing trees and vegetation minimizes the natural cooling effects of
shading and evaporation of water from soil and leaves (evapotranspiration).
Tall buildings and narrow streets can heat air trapped between them and
reduce air flow. Waste heat from vehicles, factories, and air conditioners
may add warmth to their surroundings, further exacerbating the heat island
effect. Heat islands can occur year-round during the day or night. Urbanrural temperature differences are often largest during calm, clear evenings.
This is because rural areas cool off faster at night than cities, which retain
much of the heat stored in roads, buildings, and other structures. As a
result, the largest urban-rural temperature difference, or maximum heat
island effect, is often three to five hours after sunset. Other contributing
factors to the heat island effect include:
Name: ___________________________
Earth Science
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Date: __________
Unit: Insolation
Size and shape of cities—aerodynamically, cities have a very different
shape than rural areas. Tall buildings act as obstacles and reduce wind
speeds.
Urban deserts—cities can be thought of as virtual deserts with almost no
vegetation and materials that are almost completely impermeable to rain.
This combination leads to a lack of evapotranspiration, which increases
sensible heat.
Urban canyons—the tall canyons formed by city buildings trap radiant
energy in their walls. Comparisons of this "canyon effect" in European and
North American cities suggest that areas with denser and taller buildings will
more rapidly develop heat islands.
Humidity effects—although there is little difference in the amount of water
that cities and countrysides retain in their atmospheres (absolute humidity),
the higher urban temperatures effectively lowers the relative humidity (since
warm air can hold more water than cold air).
Urban haze—The haze of air pollution that hangs over many cities can act
as a miniature greenhouse layer, preventing outgoing thermal radiation
(heat) from escaping from urban areas.
Anthropogenic heat—The release of heat from the burning of fossil fuels
can also raise urban temperatures. On a typical winter day, Manhattan
releases four times more energy from burning fossil fuels than the amount
of energy that comes into the urban area from the Sun.
Are Heat Islands and Global Warming Related?
Heat islands describe local-scale temperature differences, generally
between urban and rural areas. In contrast, global warming refers to a
gradual rise of the earth's surface temperature. While they are distinct
phenomena, summertime heat islands may contribute to global warming by
increasing demand for air conditioning, which results in additional power
plant emissions of heat-trapping greenhouse gases. Strategies to reduce
heat islands, therefore, can also reduce the emissions that contribute to
global warming. The heat island effect can also complicate studies of longterm trends. By accurately measuring heat islands, scientists can remove
the heat island effect from global temperature records.
Standards
New York State
2.1a Earth systems have internal and external sources of energy, both of which create heat.
2.1b The transfer of heat energy within the atmosphere, the hydrosphere, and Earth’s interior results in
the formation of regions of different densities. These density differences result in motion.
2.2a Insolation (solar radiation) heats Earth’s surface and atmosphere unequally due to variations in
characteristics of the materials absorbing the energy such as color, texture, transparency, state of matter,
and specific heat.
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Use the picture above to place them items in order of albedo. The first one
has been done for you.
Urban Material
1. White paint
2.
3.
4.
5.
6.
7.
8.
9.
10.
Albedo
0.50 – 0.90
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Procedures
1. Make a hypothesis about what area of New York City would have the
highest nighttime surface temperatures. Provide a scientific
explanation for you hypothesis.
Problem: Which location in New York City would have the highest nighttime
temperatures?
Hypothesis:
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
2. Compare the Landsat images on surface temperature for NYC for July,
August, and September.
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
3. Record your observations. What patterns do you notice? Which month
is the hottest? How do you know? What two variables did they keep
the same in taking the satellite image of New York City?
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Observations: What are the top three building types that use the most
energy during a heat wave?
1.
2.
3.
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Observation: What do you notice about the graph? Which area seems to be
the coolest? Why?
Observation: What do you notice about the graph? Which area seems to be
the coolest? Why?
Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
Analysis and Conclusion
1. What is an Urban Heat Island? What is the main cause of a UHI?
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2. Where does waste heat come from?
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3. When is the maximum heat island effect?
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4. Describe how humidity affects UHI?
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5. Using the diagram from the Various Urban Environment Albedos, what
urban material absorbs the most heat energy?
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6. If June 21 is the summer solstice, then why is it hottest in August and
not in June?
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Name: ___________________________
Earth Science
Date: __________
Unit: Insolation
7. Why do scientist need to look at energy consumption on days of
extreme heat?
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8. Why do scientists use the surface temperature of Central Park to
understand the Urban Heat Island?
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Links
1. Skin of the Big Apple: Characterizing the Surface Heat Island of New
York City http://www.epa.gov/hiri/resources/pdf/SurfaceUHI_EPA4.pdf
2. Variations in New York city’s urban heat island strength over time and
space http://pubs.giss.nasa.gov/docs/2008/2008_Gaffin_etal.pdf