On August 7, when the thermometer reached a high of 93 degrees, a squad of 85 temperature detectives fanned out across Houston and Harris County. Their objective: Map the area's urban heat.

Organizers of the one-day endeavor pinpointed 320 square miles of Houston and Harrison County for collection of data about urban heat. Hardware attached to cars and bicycles traveling on predetermined routes took temperature and humidity readings during three one-hour periods: 6-7 am, 3-4 pm, and 7-8 pm.

The devices tracked temperature changes throughout the day in places featuring various characteristics, such as lots of green space, pavement or buildings. In all, the "street scientist" volunteers measured temperature and humidity in 32 heat-mapping pockets covering 10 square miles each.

The heat-mapping initiative was coordinated by the Houston Harris Heat Action Team, a collaboration of the Nature Conservancy of Texas, Houston Advanced Research Center, City of Houston, and Harris County Public Health. The team's corporate partners are Lowe's and Shell.

The team says urban areas are especially prone to high temperatures due to a combination of hard surfaces (buildings and roads), limited vegetation (such as trees), and heat generators like cars and factories.

"This problem, known as the urban heat island effect, can create issues for human health, infrastructure, and quality of life. Understanding how temperatures vary based on qualities of the natural and built landscape can inform how we reduce the impacts of rising summer temperatures in our communities," the team says.

Marissa Aho, the city of Houston's chief resilience officer, says the heat-mapping data will be available this fall through an open-source platform. Aho offers a heat-mapping project in Honolulu as an example of how Houston's data will be presented.

The Resilient Houston plan, released in February by Houston Mayor Sylvester Turner, called for a heat-mapping effort like the one carried out August 7 and outlined ways to reduce urban heat, such as planting 4.6 million new native trees over the next 10 years and retrofitting roofs to decrease heat absorption. Aho says the heat-mapping data will bolster initiatives to lessen the "urban heat island" effect.

"Houstonians do not prepare for heat like we prepare for hurricanes, but we should," Turner says in a release. "Houston is getting hotter, and we need science and data to help identify where the greatest impacts are so we can keep Houstonians safer and our city more resilient."

According to the U.S. Department of Homeland Security, extreme heat — defined as at least two consecutive days with temperatures above 90 degrees — ranks as the country's No. 1 cause of weather-related deaths. A 2017 study published by the National Resources Defense Council found the Houston area averaged 18 dangerously hot summer days per year from 1975 to 2010. Without any action to combat urban heat, Houston's annual number of days hit by dangerous summer heat could rise to 80 from 2046 through 2055 and 90 from 2091 to 2100.

Urban heat "leaves vulnerable communities susceptible to the dangers of stress and stroke, leads to higher ozone levels, and reduces the quality of life for all residents of the region — creating especially dangerous conditions for communities already striving to overcome historic obstacles around access and resources, as well as those who engage in outdoor work and recreation," according to the release from the Houston Harris Heat Action Team.

Aside from the human toll, urban heat exacts a financial toll. A 2017 study by researchers in the United Kingdom, Mexico, and the Netherlands indicates overheated cities face climate-change costs at least twice as high as the rest of the world due to urban heat islands.

Organizers of Houston's heat-mapping project note that last August was the second warmest on record in the city, with seven consecutive days when the temperature topped 100 degrees. As climate change takes hold and Houston continues to expand, "these heat-related challenges continue to be exacerbated," the release states.

Jaime González, Houston Healthy Cities Program director at the Nature Conservancy, says the heat-mapping data gathered August 7 will help determine where to plant trees, install "green" roofs, and promote other heat-mitigation tactics.

"We have a number of nature-first solutions in our toolkit that can help us cool our cities, but the first step in combating climate- and infrastructure-caused urban heat is to know exactly where to start," González says.

Houston was one of 13 U.S. communities chosen to participate in this summer's Heat Watch program, led by Portland, Oregon-based environmental services company CAPA Strategies LLC and backed by the National Oceanic and Atmospheric Administration (NOAA).