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San Antonio “Hot Islands”
Sandra Ytuarte December 1, 2004 Noreen Castellano
What is a “Hot Island”?
On warm summer days the air in urban areas
can be 6-8°F hotter than the surrounding
areas.
In the downtown areas of cities, buildings
and pavements made of dark materials
absorb the sun’s rays instead of reflecting
then away.
These higher temperatures contribute to the
summer warming trends that occur in these
urban areas.
What causes a “Hot Island”?
Buildings, Concrete & Asphalt in the
downtown areas made of dark
materials.
The lack of vegetation in city which
does not provide shade for the buildings
or allow for the air to be cool.
What problems are caused by
“Hot Islands”?
Higher temperatures in the city lead to
an increase in air conditioning use,
which makes the downtown area more
expensive to maintain.
Higher temperatures also raise pollution
levels in the downtown areas which is a
health concern.
Factors Contributing to
“Hot Islands”
Dark roofing materials which absorb
more heat from the sun.
Pavements made of black asphalt
concrete absorb the energy from the
sunlight and convert it into thermal
energy – the pavements get hotter.
Lack of vegetation which does not allow
for shading and cool ambient air.
Roofing Materials
The solar reflectance index (SRI) is a
measure of how hot materials are in the
sun
A traditional roofing material has an SRI
between 5% (brown shingles) and 20%
(green shingles)
Roofing Materials
In the past white shingles were very
popular due to their high SRI of 35%.
Unfortunately they lost popularity due
to them getting dirty easily.
Currently light colored roofing materials
are preferred.
They increase the solar reflectivity of a
building and lower it’s temperature.
Roofing Materials
Black Shingle Conventional Advanced
White Shingle White Shingle
Reflectance = 5% Reflectance = 29% Reflectance = 60%
Temperature = Temperature = Temperature =
180°F 157°F 128°F
Solar Reflectivity of Roofing
Materials
Pavements Reflectivity
Albedo or reflectivity is the ratio of the
amount of light reflected from a
material to the amount of light shined
on the material.
For pavements the sunlight is converted
into thermal energy and the pavement
gets hotter.
Pavements Reflectivity
A lower albedo would suggest that more light
is absorbed by the pavement and the
pavement is hotter.
A higher albedo would suggest that less
energy is absorbed and the pavement is
cooler.
The reduction in the temperature of the
pavement would also reduce the heat island
effect.
Albedos of Pavements
Dark fresh Asphalt
Albedo=0.05, with a temperature of 123°F
Aged Asphalt
Albedo =0.15, with a temperature of 115°F
Asphalt with a coating
Albedo =0.51, with a temperature of 88°F
Albedos of Pavements
Albedo of Pavement
Vegetation in the City
The lack of vegetation in a city does not
allow trees, shrubs, and other plants to
shade the buildings & pavements.
When vegetation is present the plants
and trees intercept solar radiation and
cool the air.
This is called “Evapotranspiration”.
Evapotranspiration
Evapotranspiration occurs when plants
secrete or “transpire” water through
pores in their leaves – this is similar to
how people sweat.
This water draws heat as it evaporates,
cooling the air in the process.
Vegetation in the City
A single mature, properly watered tree
with a crown of 30 feet can
“evapotranspire” up to 40 gallons of
water in a day.
This is the benefit of having a
downtown area full of vegetation.
Evapotranspiration
Vegetation in the City
Vegetation in the City
Factors that would reduce
“Hot Islands”
Light roofing materials made of white
shingles with a high reflectance.
Pavements in the downtown area with a
high albedo.
The presence of plants and trees in the
city which cool the air by
“Evapotranspiration”.
Factors that would reduce
“Hot Islands”
Cool roofs & pavements – can reflect the solar
radiation, and reduce the heat being created.
Vegetation in the cities – would reduce the ambient
temperature through “evaportranspiration”.
Mitigation strategies of planting trees and shrubs,
installing reflective materials for roofs and pavements
in the urban areas.
Evaluate the mitigation strategies in a year, record
and evaluate the data to see if there has been any
change in temperature for the urban areas.
San Antonio“Hot Islands”
Each city’s urban heat island varies based on
the city structure and thus the range of
temperatures within the island vary as well.
In our stone-like cities, they only slowly loose
heat at night, thus causing the greatest
temperature differences between the city and
country side to take place at night.
San Antonio“Hot Islands”
In this project the temperatures in the
downtown San Antonio area were
recorded during the day and evening
for the month of July 2004.
Data Acquisition
NASA Earth Observing System Data Gateway.
The data will be ordered through Land Processes DAAC (LP
DAAC) User Services from the U.S. Geological Survey.
July 1, 2004 through August 1, 2004, and time range - 2:00
p.m. MODIS/Aqua (MOD 11 EOS PM) was used to capture data
Day : afternoon (2pm)
Night
This information is then downloaded and the MODIS Tool MRT
is used the transfer the HDF files to tif files.
These tif files are then projected to UTM14 and then ENVI
software is used to cut sub sets and stack 30 images into one
image file.
Envi software was used to produce images to show these
temperature ranges of the San Antonio Area.
Excel software was used to graph the temperatures for Day and
Night temperature ranges.
Temperature Data Conversions
The results were taken from the density slice range screen from
Envi
Temperature Data
Conversions
The temperatures were converted to °F
by the following formula.
Convert from °K to °C
Value (DN) x 0.02 = °K
°K – 273 = °C
Convert from °C to °F
Value °C x 1.8 + 32 = °F
3-Dimensional San Antonio Area
July 13th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
Cyan 81.07 84.20
The hottest area for this day ranges from 81.07°F - 84.20°F.
This is shaded in the color Cyan which is in the Southeast
portion of San Antonio. The other temperature ranges are the
following: 32.00°F- 66.06 °F in the color Black, 66.09°F-
67.93°F in the color Yellow , 67.96°F- 69.80 °F in the color
Maroon , 69.84°F- 71.67 °F in the color Sea Green , 71.71°F-
73.54°F in the color Red, 73.58 °F- 75.42°F in the color Green,
75.45°F - 77.29°F in the color Brown , 77.32°F - 79.16°F in the
color Blue, and 79.20°F- 81.03°F in the color Orchid
July 14th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Lime Green 73.58 75.42
The hottest area for this day ranges from 73.58 °F- 75.42°F.
This is shaded in the LimeGreen color which is in
Southeast the portion of San Antonio. The other
temperature ranges are the following: 32.00°F- 66.06°F in
the color Black, 66.09°F - 67.93°F in the color Yellow,
67.96°F- 69.80°Fin the color Maroon, 69.84 °F- 71.67 °F in
the color Sea Green, and 71.71 °F- 73.54°F in the color
Red.
July 15th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
Cyan 81.07 84.20
The hottest area for this day ranges from 81.07°F - 84.20°F.
This is shaded in the color Cyan which is in the Southeast
portion of San Antonio. The other temperature ranges are the
following: 32.00°F- 66.06 °F in the color Black, 66.09°F-67.93°F
in the color Yellow , 67.96°F- 69.80 °F in the color Maroon ,
69.84°F- 71.67 °F in the color Sea Green , 71.71°F- 73.54°F in
the color Red, 73.58 °F- 75.42°F in the color Green, 75.45°F -
77.29°F in the color Brown , 77.32°F - 79.16°F in the color Blue,
and 79.20°F- 81.03°F in the color Orchid
July 16th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Lime Green 73.58 75.42
The hottest area for this day ranges from 73.58 °F- 75.42°F.
This is shaded in the Lime Green color which is in the
Downtown Center and some in the Southeast the portion of
San Antonio. The other temperature ranges are the
following: 32.00°F- 66.06°F in the color Black, 66.09°F -
67.93°F in the color Yellow, 67.96°F- 69.80°Fin the color
Maroon, 69.84 °F- 71.67 °F in the color Sea Green, and
71.71 °F- 73.54°F in the color Red.
July 19th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
Cyan 81.07 84.20
The hottest area for this day ranges from 81.07°F -
84.20°F. This is shaded in the color Cyan which is in the
Southeast portion of San Antonio. The other
temperature ranges are the following: 32.00°F- 66.06 °F
in the color Black, 66.09°F-67.93°F in the color Yellow ,
67.96°F- 69.80 °F in the color Maroon , 69.84°F- 71.67 °F
in the color Sea Green , 71.71°F- 73.54°F in the color
Red, 73.58 °F- 75.42°F in the color Green, 75.45°F -
77.29°F in the color Brown , 77.32°F - 79.16°F in the
color Blue, and 79.20°F- 81.03°F in the color Orchid.
July 20th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
Cyan 81.07 84.20
Coral 84.24 86.11
The hottest area for this day ranges from 81.07°F -
84.20°F. This is shaded in the color Cyan which is in
the Southeast portion of San Antonio. The other
temperature ranges are the following: 32.00°F- 66.06
°F in the color Black, 66.09°F-67.93°F in the color
Yellow , 67.96°F- 69.80 °F in the color Maroon ,
69.84°F- 71.67 °F in the color Sea Green , 71.71°F-
73.54°F in the color Red, 73.58 °F- 75.42°F in the
color Green, 75.45°F - 77.29°F in the color Brown ,
77.32°F - 79.16°F in the color Blue, and 79.20°F-
81.03°F in the color Orchid.
July 24th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
Cyan 81.07 84.20
The hottest area for this day ranges from 84.24°F - 86.11°F.
This is shaded in the color Coral which is in the Southeast
portion of San Antonio. The other temperature ranges are
the following: 32.00°F- 66.06 °F in the color Black, 66.09°F-
67.93°F in the color Yellow , 67.96°F- 69.80 °F in the color
Maroon , 69.84°F- 71.67 °F in the color Sea Green , 71.71°F-
73.54°F in the color Red, 73.58 °F- 75.42°F in the color
Green, 75.45°F - 77.29°F in the color Brown , 77.32°F -
79.16°F in the color Blue, 79.20°F- 81.03°F in the color
Orchid, and 81.07°F - 84.20°F Cyan.
July 27th Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
The hottest area for this day ranges from77.32°F - 79.16°F.
This is shaded in the color Blue which is in Southeast the
portion Southeast portion of San Antonio. The other
temperature ranges are the following: 32.00°F- 66.06°F in
the color Black, 66.09°F - 67.93°F in the color Yellow,
67.96°F- 69.80°Fin the color Maroon, 69.84 °F- 71.67 °F in
the color Sea Green, 71.71 °F- 73.54°F in the color Red,
and 73.58 °F- 75.42°F Green.
July 31st Night Temperature
Ranges
Color °F °F
Black 32.00 66.06
Yellow 66.09 67.93
Maroon 67.96 69.80
Sea Green 69.84 71.67
Red 71.71 73.54
Green 73.58 75.42
Brown 75.45 77.29
Blue 77.32 79.16
Orchid 79.20 81.03
The hottest area for this day ranges from 79.20°F-
81.03°F. This is shaded in the color Cyan which is in the
Southeast portion of San Antonio. The other temperature
ranges are the following: 32.00°F- 66.06 °F in the color
Black, 66.09°F-67.93°F in the color Yellow , 67.96°F- 69.80
°F in the color Maroon , 69.84°F- 71.67 °F in the color Sea
Green , 71.71°F- 73.54°F in the color Red, 73.58 °F- 5.42°F
in the color Green, 75.45°F - 77.29°F in the color Brown ,
and 77.32°F - 79.16°F in the color Blue.
July 4th Day Temperature
Ranges
Color °F °F
Black 32.00 83.62
Red 89.28 91.11
Green 91.15 92.98
Sienna 93.02 94.86
Blue 94.89 96.73
Orchid 96.76 98.60
The hottest area for this day ranges from 96.76 °F -
98.60 °F. This is shaded in the orchid color which is the
Northeast part of San Antonio. The other temperature
ranges are the following: 94.89°F - 96.73°F in the blue
color, 93.02 °F - 94.86°F in the sienna/brown color,
91.15°F- 92.98°F in the green color, and 89.28°F - 91.11.
°F in the red color.
July 5th Day Temperature
Ranges
Color °F °F
Black 32.00 89.60
Thistle 99.36 94.96
Maroon 95.00 102.16
Green 95.00 100.04
Purple 98.64 102.16
Cyan 100.08 104.11
Yellow 102.24 106.02
Red 104.14 107.92
Orange 106.05 109.36
The hottest area for this day ranges
from106.05°F-109.36°F. This is shaded in the
Orange color which is the Northwest central
portion of San Antonio. The other temperature
ranges are the following: 0.00°F - 89.60°F in
the Black color , 99.36°F-94.96°F in the Thistle
color , 95.00°F -102.16°F in the Maroon color,
95.00°F-100.04°F in the Green, 98.64°F-02.16°F
in the Purple color , 100.08 °F- 104.11°F in the
Cyan color, 102.24°F -106.02°F in the Yellow
color, 104.14°F -107.92°F in the Red color, ,
107.96°F -116.56°F Blue color.
July 13th Day Temperature
Ranges
Color °F °F
Black 32.00 84.20
Brown 91.44 95.00
Blue 95.04 98.60
Orchid 98.64 102.20
Sea Green 102.24 105.80
Orange 105.84 109.40
Hot Pink 109.44 113.00
Yellow 113.04 116.60
Purple 116.64 120.20
The hottest area for this day ranges from
116.64°F – 120.20°F. This is shaded in the
Purple color which is in the Center of
Downtown San Antonio. The other
temperature ranges are the following:
32.00°F-84.20°F in the color Black, 91.44°F -
95.00°F in the color Brown, 95.04°F -
98.60°F in the color Blue , 98.64°F -
102.20°F in the color Orchid, 102.24°F -
105.80°F in the color Sea Green , 105.84°F -
109.40°F in the color Orange, 109.44°F-
113.00°F in the color Hot Pink, and
113.04°F-116.60°F in the color Yellow.
3 Dimensional of July 13th
July 18th Day Temperature
Ranges
Color °F °F
Black 32.00 87.80
Blue 87.84 98.60
Orchid 98.64 102.20
Cyan 102.24 105.80
Orange 105.84 109.40
Green 109.44 113.00
Red 113.04 114.91
Brown 114.94 116.60
Yellow 116.64 119.30
The hottest area for this day ranges from116.64°F -
119.30°F. This is shaded in the Yellow color which is
in the Upper Northern part of San Antonio. The
other temperature ranges are the following: 32.00°F-
87.80°F in the color Black, 87.84°F-98.60°F in the
color Blue, 98.64°F-102.20°F in the color Orchid,
102.24°F-105.80°F in the color Cyan, 105.84°F-
109.40°F in the color Orange , 109.44°F- 113.00°F in
the color Green, 113.04°F -14.91°F in the color Red,
and 114.94°F -116.60°F in the color Brown.
Night Average Temperature
Results Night Temperatures
90.00
80.00
70.00
July 3rd °F
Temperature Farenheit
60.00 July 4th °F
July 5th °F
50.00 July 6th °F
July 9 th °F
40.00 July 10 th °F
July 14 th °F
30.00 July 17 th °F
July 21 th °F
20.00
10.00
0.00
Range 1 Range 2 Range 3 Range 4 Range 5 Range 6 Range 7 Range 8 Range 9 Range Range
: Black : Yellow : Maroon : Sea : Red : Green : Brow n : Blue : Orchid 10 : 11 :
Green Cyan Coral
Range
Day Average Temperature
Results
Day Temperatures
140.00
120.00
100.00
Temperature Farenheit
80.00 July 4th °F
July 5th °F
July 13th °F
60.00
July 18th °F
40.00
20.00
0.00
1 2 3 4 5 6 7 8 9 10
Range
