THE WOODLANDS, TEXAS (Feb. 25, 2025) – The results are in from the 2024 Houston Harris Heat Action Team (H3AT) Mapping Campaign, the country’s largest single-day, community-led heat mapping effort. Conducted on August 10, 2024, the campaign engaged more than 150 volunteers who collected temperature and humidity data across 69 routes spanning Houston and Harris County. The data provides critical insights into the urban heat island effect and will inform solutions to mitigate extreme heat in vulnerable communities.
Data was captured during three time periods – morning, afternoon, and evening – which allowed researchers to compare intraday warming and overnight cooling differences.
The data show what many Houston residents already know—heat is not experienced equally across the city. Areas with open greenspace, tree shading and less development stay cooler than areas with lots of concrete, dense development, and little tree cover. In some neighborhoods, the difference was drastic. The difference between the “coolest” and hottest areas was 14 degrees in the afternoon.
Interactive data maps and street-by-street temperatures are available at the H3AT website.(www.h3at.org/).
“A 14-degree difference during a hot Houston day can be the difference between discomfort and dangerous health risks,” said Stephanie Piper, Ph.D., Community Development and Resilience Research Associate at HARC (Houston Advanced Research Center). “People who are already vulnerable — those without air conditioning, those who live in older buildings, or the elderly — face even greater risks from extreme heat.”
The H3AT campaign identified areas in Houston where temperatures soared well above the city’s average, increasing the risk of heat-related illnesses such as dehydration and heat stroke. Data collected during the campaign will be used to guide urban planning efforts, inform tree planting initiatives, and develop cooling strategies for public spaces.
“The data goes beyond documenting the problem,” Piper said. “They help us prioritize areas where heat mitigation can have the most impact for the most people.”
H3AT conducted its first campaign in Houston in 2020. The 2024 campaign more than doubled the square mileage covered.
More than 150 volunteers covered 3,446 miles across three time periods—morning, afternoon, and evening—to capture temperature variations throughout the day. Areas surveyed included Alief, Sunnyside, Fifth Ward, Pasadena, Greenspoint, and other heat-prone neighborhoods.
“The fact that so many volunteers wanted to map their own neighborhoods shows just how aware residents are of the extreme heat issue and their desire to be part of a data-driven solution,” Piper said. “With data in hand, we can now design for real, evidence-based interventions.”
The 2024 H3AT mapping data will support tree-planting efforts in public spaces, prioritizing areas with high heat exposure, low canopy coverage, and significant tree loss. Additionally, the data will help decision-makers explore other cooling interventions, like reflective pavements, shaded bus stops, and cooling infrastructure in high-traffic community areas.
Funding for the campaign was provided by the Inflation Reduction Act and the USDA Forest Service’s Urban and Community Forestry Program. The initiative is part of ForUsTree: Creating an Inclusive Community Canopy, a broader effort to enhance tree cover, build resilience, and create green job opportunities in communities across Houston and Harris County. As part of this commitment to inclusive environmental solutions, this institution is an equal opportunity provider.
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About The Houston Harris Heat Action Team (H3AT)
The Houston Harris Heat Action Team (H3AT) is a collaborative effort by HARC, the City of Houston, Harris County Public Health, Harris County Office of County Administration, Harris County Precinct 4, the Student Conservation Association, the National Weather Service, and CAPA Strategies. The initiative aims to assess and address the impacts of extreme heat in Houston and Harris County through data-driven solutions, community engagement, and policy advocacy.
About The Houston Advanced Research Center (HARC)
HARC is an independent, non-partisan and non-profit research, policy and program implementation organization that forges sustainability solutions and improves the quality of life of people for generations to come. Learn more at www.harcresearch.org or follow us on Instagram, LinkedIn, Facebook, or Twitter.
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