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Hot zones: Urban Heat Islands

Taller buildings and increased impermeable surfaces creating hotter temperatures in Bryan-College Station
Published: Jul. 15, 2021 at 4:47 PM CDT
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BRYAN, Texas (KBTX) - Urban heat islands are metropolitan areas that are hotter than their outlying, more “green” regions. Greater heat impacts are most felt during the summer months, where more developed areas can experience peak temperatures that are 15° to 20° hotter than nearby areas with more trees and less pavement.

A recent study created an index to evaluate the intensity of urban heat islands in 159 cities across the United States. The intensity score for Bryan-College Station was found to be 6° -- that is how much hotter industrial, downtown, and areas with a lack of greenery can be on any given day compared to more rural portions of Brazos County and city parks. Factors that determined this local index score: Increased paved -- both concrete and asphalt -- surfaces, loss of green space, increasing population density, and increase in taller buildings and apartment complexes being erected.

HOW MUCH HOTTER IS BRYAN-COLLEGE STATION?

The index score, created by Climate Central, is a temperature representing the potential difference in average temperature for the city compared to its less developed surroundings. Results show the index temperature score ranges from less than 5° to nearly 9°. Each score represents an average for the entire city, and certain neighborhoods or areas of a city that will likely be cooler or hotter, depending on vegetation and other factors. The index shows Bryan-College Station may be up to 6° warmer on average, although, within the city, residents living next to a park will be cooler than those living near a parking lot or major roadway.

Top 10 cities urban heat island intensity

CityIndex Score (°F)Critical Components
1. New Orleans8.94Albedo, impermeable surface
2. Newark, N.J.7.71Impermeable surface, building height, population density
3. New York City7.62Building height, impermeable surface, population density
4. Houston7.46Impermeable surface, albedo
5. San Francisco7.37Building height, impermeable surface, population density
6. Boston7.24Building height, population density
7. Chicago7.24Building height, impermeable surface, population density
8. Miami7.24Building height, impermeable surface
9. Baltimore, Md.7.08Building height, impermeable surface
10. Providence, R.I.7.08Building height, impermeable surface

WHAT ARE CRITICAL COMPONENTS OF HEAT ISLANDS?

Heat islands are strongly influenced by albedo, which measures whether a surface reflects sunlight or absorbs and retains the sun’s heat. Other factors include the number of impermeable surfaces, such as buildings, driveways, sidewalks, roads, and parking lots. Hard, dry surfaces provide less shade and moisture than natural landscapes and contribute to higher temperatures. Other components include a lack of greenery and trees, the dimensions and heights of buildings, and heat created by human activities like running engines and air conditioners.

WHAT ARE THE IMPACTS?

Extreme urban heat is a public health threat. It amplifies air pollution and creates dangerous conditions for people working outside or living in buildings without air conditioning.

WHAT CAN BE DONE? WHAT IS THE SOLUTION?

  • Planting Trees: particularly along paved streets and large parking lots.
  • A Green Roof or rooftop garden: a vegetative layer grown on a rooftop can provide shade and lower temperatures of the roof surface and surrounding air.
  • Cool Roofs: made of highly reflective and emissive materials that remain cooler than the traditional materials and help reduce energy use.

The EPA maintains a Community Actions Database of measures that communities are taking to mitigate the heat island effect in their area. Neither Bryan nor College Station have submitted plans to the EPA to help mitigate the increasing heat island effect in either city.

The full report released by Climate Central can be found here.

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