A new report takes the temperature of urban heat islands across the U.S., and Houston lands in the hotter-than-you-know-what category.

The report, released July 14 by the nonprofit news organization Climate Central, ranks Houston the fourth worst place among the country's urban heat islands. Houston sits behind New Orleans, holding down the No. 1 spot, with Newark, New Jersey, at No. 2 and New York City at No. 3.

"Even for a Houstonian, it's easy to think first of flooding or hurricanes when it comes to regional climate impacts, but increases in daytime and nighttime temperatures at the rate we've seen since the 1970s can do as much — if not more — damage," the Nature Conservancy of Texas notes in a July 2020 news release.

Climate Central emphasizes that extreme urban heat is a public health threat. Texas, Arizona, and California accounted for 37 percent of the country's heat-related deaths between 2004 and 2018, according to U.S. Centers for Disease Control and Prevention (CDC) data released in 2020.

According to the Climate Central report, Houston scored so high because of the city's sizeable share of impermeable surfaces, such as asphalt, concrete, stone, and brick. Impermeable surfaces absorb heat and prevent water from penetrating them.

Climate Central describes urban heat islands as big urban locations that are hotter that outlying areas, especially during the summer. Neighborhoods in a highly developed city can experience peak temperatures that are 15 to 20 degrees above nearby places that have more trees and less pavement, the group says.

The nonprofit created an index to evaluate the intensity of urban heat islands and applied it to 159 cities across the U.S., with Houston claiming the No. 4 spot.

"Heat islands are heavily influenced by albedo, which measures whether a surface reflects sunlight or absorbs and retains the sun's heat," Climate Central says. "Other factors include the amount of impermeable surface, lack of greenery and trees, building height, and heat created by human activities."

Results of a one-day study carried out last August support Climate Central's conclusion about Houston.

The study mapped out heat islands across 320 square miles of Houston and Harris County. More than 80 community scientists fanned out to sample temperatures during three one-hour periods last August 7.

The hottest point measured during the heat-mapping day was 103.3 degrees just southwest of the Galleria on Richmond Avenue near Chimney Rock Road. At the same time, volunteers recorded a temperature of 86.2 degrees about 20 miles to the east on Woodforest Boulevard in Channelview. The result: a 17.1-degree temperature swing between Houston and Harris County's hottest and coolest areas at the same point in time.

The Houston Harris Heat Action Team — a collaboration among the Houston Advanced Research Center, the City of Houston, Harris County Public Health, and the Nature Conservancy of Texas — sponsored the heat-mapping exercise with financial support from Lowe's and Shell.

"The data has identified Houston's 'hot spots' and shows that some Houstonians are impacted by urban heat island effect more than others," Houston Mayor Sylvester Turner said in a January news release about the heat-mapping study. "We will work with partners to target our cooling and health strategies … to better help Houstonians beat the heat."

The heat-mapping event was conducted in conjunction with Resilient Houston, the city's campaign to make Houston neighborhoods greener and cooler. The City of Houston says data from the heat-mapping study will help with evaluation of health risks related to extreme heat, coordination of tree plantings, installation of shade-producing structures, establishment of cooling centers, and targeted design of parks, streets, housing, and other infrastructure.

"Science shows that there is real potential to reshape our built environment and cool our cities down where it's needed most," says Suzanne Scott, director of the Nature Conservancy of Texas. "And now, armed with this data, local planners, developers, and environmental groups like ours will be able to leverage smart, cooling urban design strategies that offer multiple benefits — including climate resilience — for all residents, both human and wildlife."