Hurricane dangers and a rising Gulf of Mexico aren’t the only climate-change considerations for this U.S. city of nearly 400,000 people and over 18 million annual visitors, including to its famous Mardi Gras celebration.
New Orleans has been ranked No. 1 for its “heat islands.”
Urban “heat islands” are sections of highly-developed metropolitan areas that can experience peak temperatures running 15°-20°F hotter than nearby neighborhoods or adjoining municipalities with more trees and less pavement.
A new index and report by Climate Central, using research led by Valentino Sangiorgio, has ranked 159 U.S. cities as the most intense urban heat islands. After New Orleans comes Newark, N.J., New York City, Houston and San Francisco. Smaller cities that may not be obvious hot spots also make the top 20, including Bend, Ore., Erie, Pa., and Burlington, Vt.
Heat islands are heavily influenced by albedo, which measures whether a surface reflects sunlight or absorbs and retains the sun’s heat. Other factors include the amount of impermeable surface, lack of greenery and trees, building height and heat created by human activities. For instance, during a heat wave, air conditioning from urban buildings can add 20% more heat to the outside air, compared to regular summer weather.
|1. New Orleans||8.94||albedo, impermeable surface|
|2. Newark, N.J.||7.71||impermeable surface, building height, population density|
|3. New York City||7.62||building height, impermeable surface, population density|
|4. Houston||7.46||impermeable surface, albedo|
|5. San Francisco||7.37||building height, impermeable surface, population density|
|6. Boston||7.24||building height, population density|
|7. Chicago||7.24||building height, impermeable surface, population density|
|8. Miami||7.24||building height, impermeable surface|
|9. Baltimore, Md.||7.08||building height, impermeable surface|
|10. Providence, R.I.||7.08||building height, impermeable surface|
|11. Sacramento, Calif.||7.08||building height, impermeable surface|
|12. Salinas, Calif.||7.08||albedo, impermeable surface|
|13. Burlington, Vt.||7.05||albedo|
|14. Bend, Ore.||6.97||albedo, impermeable surface|
|15. Cleveland, Ohio||6.97||building height, impermeable surface|
|16. Detroit||6.97||impermeable surface, building height|
|17. Erie, Pa||6.97||impermeable surface|
|18. Fresno, Calif.||6.97||impermeable surface|
|19. Lafayette, La.||6.97||impermeable surface, building height|
|20. McAllen, Texas||6.97||impermeable surface|
About 85% of the U.S. population lives in metropolitan areas. The researchers stressed that malls, parking lots, hospital campuses, playgrounds — anywhere with more impervious surfaces and fewer trees can create a heat island effect, even if they are located in what might be considered a rural or suburban area.
Record-setting temps are in focus as the U.S. West suffers under a historic drought and other extreme weather has intensified the focus on the impacts from climate change in aggravating more typical swings in weather conditions. Increasingly, summer temperatures are stretching into the “shoulder seasons” of spring and fall, meteorologists and climate-change experts have said.
Urban heat islands can exacerbate the impact of these heat waves, compromising health and comfort, and often creating dangerous conditions for many vulnerable populations.
Extreme heat is the leading cause of death among weather-related fatalities over the past 30 years, according to the National Weather Service. The 1995 Chicago heat wave was one of the deadliest climate disasters in U.S. history, killing 739 people, mostly elderly and poor.
Select areas around the country now brace for rolling blackouts or power outages, which have the potential to become life-threatening in a matter of hours for those most vulnerable.
Short-term help typically comes in the form of alerts and relief on energy bills.
But smarter planning and development can limit the negative effects of heat islands.
• Planting trees, particularly along paved streets. Shaded surfaces may be 20–45°F (11–25°C) cooler than the peak temperatures of unshaded surfaces. Trees also absorb carbon dioxide (a greenhouse gas), improve air quality, and can slow down storm water runoff. American Forests have created an interactive tool to look at
“tree equity” at the local level.
• A green roof or rooftop garden.
• Cool roofs that are made of highly reflective and emissive materials that remain cooler than traditional materials.
• Cool pavements, or whitewashing roads and sidewalks, which is more complicated than roofs. In cities with urban canyons, the sunlight may not even reach the street level long enough to make a significant difference. In places like Los Angeles, a cool pavement study showed that heat was reflected off the white surface, but
onto pedestrians and made people feel hotter.
• Varying the height of new buildings to increase air circulation and considering the layout of streets and buildings. This is a holistic but much more long-term approach for cities and planners.
• ACEEE maintains a database tracking mitigation efforts for urban heat islands across most major U.S. cities.
• Solar panels have also been shown to provide shade and reduce the heat island effect.