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Louisville's Urban Heat Islands are Among Most Intense, Fastest-Growing in the U.S., Report Says

Areport released Wednesday by a climate change nonprofithas ranked Louisville among the top 10 U.S. cities with a serious urban heat island effect.Urban heat islands are areas where cities are substantially hotter than surrounding rural areas. This is exacerbated by factors such as large swathes of paved surfaces and declining tree canopies.“The materials that make up cities like concrete and asphalt absorb a lot of heat and cities also have more cars and industry that generates heat,” report author Alyson Kenward said. “And urban areas tend to have fewer trees and less vegetation than rural areas and it’s those things, the shade and the moisture that they provide that helps keep rural areas cooler.”In Louisville, it’s a known problem: other studies have ranked the city’s urban heat island as the fastest-growing in the nation.The report from Climate Central confirmed that Louisville’s UHIs are among the worst in the country, and this heat has real implications for the city’s air quality.Louisville had the distinction of being the only city to be included in all of the report’s top ten lists. Louisville has one of the most intense urban heat islands in the country, as well as one of the fastest-growing urban heat islands.Climate Central’s researchers found that in Louisville:

  • urban areas were on average 4.8 degrees Fahrenheit warmer than rural areas over the past ten years;
  • nighttime temperatures in urban areas were on average seven degrees warmer than rural areas over the past 10 years
  • urban areas had 23 more days above 90 degrees than rural areas over the past 10 years.
  • temperatures are increasing an average of 0.65 degrees per decade since 1970.
  • nighttime temperatures are increasing an average of 0.61 degrees per decade since 1970

Hotter temperatures bring with them health implications. Besides heat-related illnesses like heatstroke,  heat exacerbates problems like ozone, said Dr. Howard Frumkin of the University of Washington’s School of Public Health.“When cities become hotter, the ozone levels in cities tend to rise,” he said. “Ozone is toxic to our airways. Higher ozone results in irritation and inflammation of the airways and that translates into more respiratory symptoms, especially among people with asthma or bronchitis or other underlying conditions of the airways.”Louisville has had problems with high ozone levels in the past; there were 23 days in 2012 when the area’s ozone levels exceeded the federal standard. The city has also begun addressing its declining tree canopy. The preliminary results of a city-wide study have found that a core part of the city lost nine percent of its tree canopy from 2004 to 2012.