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 ShingleConventional White Shingle Advanced White Shingle Reflectance = 5% Temperature = 180°F Reflectance = 29% Temperature = 157°F Reflectance = 60% Temperature = 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

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 = °F

3-Dimensional San Antonio Area

July 13 th Night Temperature Ranges The hottest area for this day ranges from 81.07°F °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 °F in the color Black, 66.09°F °F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F °F in the color Green, 75.45°F °F in the color Brown, 77.32°F °F in the color Blue, and 79.20°F °F in the color Orchid

July 14 th Night Temperature Ranges The hottest area for this day ranges from °F °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 °F in the color Black, 66.09°F °F in the color Yellow, 67.96°F °Fin the color Maroon, °F °F in the color Sea Green, and °F °F in the color Red.

July 15 th Night Temperature Ranges The hottest area for this day ranges from 81.07°F °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 °F in the color Black, 66.09°F-67.93°F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F °F in the color Green, 75.45°F °F in the color Brown, 77.32°F °F in the color Blue, and 79.20°F °F in the color Orchid

July 16 th Night Temperature Ranges The hottest area for this day ranges from °F °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 °F in the color Black, 66.09°F °F in the color Yellow, 67.96°F °Fin the color Maroon, °F °F in the color Sea Green, and °F °F in the color Red.

July 19 th Night Temperature Ranges The hottest area for this day ranges from 81.07°F °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 °F in the color Black, 66.09°F-67.93°F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F °F in the color Green, 75.45°F °F in the color Brown, 77.32°F °F in the color Blue, and 79.20°F °F in the color Orchid.

July 20 th Night Temperature Ranges The hottest area for this day ranges from 81.07°F °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 °F in the color Black, 66.09°F-67.93°F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F °F in the color Green, 75.45°F °F in the color Brown, 77.32°F °F in the color Blue, and 79.20°F °F in the color Orchid.

July 24 th Night Temperature Ranges The hottest area for this day ranges from 84.24°F °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 °F in the color Black, 66.09°F °F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F °F in the color Green, 75.45°F °F in the color Brown, 77.32°F °F in the color Blue, 79.20°F °F in the color Orchid, and 81.07°F °F Cyan.

July 27 th Night Temperature Ranges The hottest area for this day ranges from77.32°F °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 °F in the color Black, 66.09°F °F in the color Yellow, 67.96°F °Fin the color Maroon, °F °F in the color Sea Green, °F °F in the color Red, and °F °F Green.

July 31 st Night Temperature Ranges The hottest area for this day ranges from 79.20°F °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 °F in the color Black, 66.09°F-67.93°F in the color Yellow, 67.96°F °F in the color Maroon, 69.84°F °F in the color Sea Green, 71.71°F °F in the color Red, °F- 5.42°F in the color Green, 75.45°F °F in the color Brown, and 77.32°F °F in the color Blue.

July 4 th Day Temperature Ranges The hottest area for this day ranges from °F °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 °F in the blue color, °F °F in the sienna/brown color, 91.15°F °F in the green color, and 89.28°F °F in the red color.

July 5 th Day Temperature Ranges The hottest area for this day ranges from106.05°F °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 °F in the Black color, 99.36°F-94.96°F in the Thistle color, 95.00°F °F in the Maroon color, 95.00°F °F in the Green, 98.64°F-02.16°F in the Purple color, °F °F in the Cyan color, °F °F in the Yellow color, °F °F in the Red color,, °F °F Blue color.

July 13 th Day Temperature Ranges The hottest area for this day ranges from °F – °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 °F in the color Brown, 95.04°F °F in the color Blue, 98.64°F °F in the color Orchid, °F °F in the color Sea Green, °F °F in the color Orange, °F °F in the color Hot Pink, and °F °F in the color Yellow.

3 Dimensional of July 13th

July 18 th Day Temperature Ranges The hottest area for this day ranges from116.64°F °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 °F in the color Black, 87.84°F-98.60°F in the color Blue, 98.64°F °F in the color Orchid, °F °F in the color Cyan, °F °F in the color Orange, °F °F in the color Green, °F °F in the color Red, and °F °F in the color Brown.

Night Average Temperature Results

Day Average Temperature Results