Houston Heat & Urban Trees

June 25, 2025

It is HOT in Houston, and getting hotter. Urban heat impacts our health, the economy, and the environment. Heat also has an unequal impact on various parts of our community, and some Houstonians live in an “urban heat island,” where temperatures are disproportionately higher. Equitable, collaborative, community-based programs to green urban spaces can improve our quality of life, reduce heat impacts, and support resilience across the city.

How hot is it? According to Houston’s Climate Impact Assessment, the annual number of days with temperatures greater than 100˚F has increased from 1 day (1971-1990) to 3 days (2001-2020). As the increase in greenhouse gas emissions continues, by the year 2100, the Houston area is predicted to reach 22 more days exceeding 100°F, 50 more nights exceeding 80°F, the hottest day of summer 7°F warmer, and summers 55 days longer than they were in 2022.(i) 

A coalition of organizations led by the Houston Advanced Research Center (HARC) conducted a one-day heat mapping campaign in August 2024 across Houston and Harris County.(ii) In the 2024 study, the highest observed temperature, in Hidden Valley, was 103˚F – a full 14˚F higher than the lowest measured temperature. (iii) The hottest neighborhoods include Gulfton, Alief, Sharpstown, and Sunnyside. (iv)These areas with consistently higher than average temperatures are called urban heat islands. 

Why does it matter? Houston heat is not just uncomfortable -- it’s downright dangerous. Between 2019 and 2023, there were 7,627 total heat-related illnesses reported in Harris County.(v) In a 2021 study, it was estimated that more than 80 additional heat-related deaths will occur with every degree Fahrenheit (°F) of temperature increase in Harris County.(vi) And the impacts are felt unequally across different parts of the population. Aside from people who work outdoors, older people and people with pre-existing health conditions like diabetes, chronic obstructive pulmonary disease (COPD), asthma, obesity, kidney disease, and dementia are at higher risk during excessive heat events. (vii)

What are some causes of excessive urban heat? Buildings trap heat and block natural airflow. Vehicles, air conditioners, and industrial facilities also generate both heat and pollution. High amounts of dark surfaces that absorb heat, like asphalt and concrete, further worsen the warm conditions.(viii) Another critical factor is that expanding development destroys tree and plant coverage, thus reducing shade and moisture, as we reported in a blog in May 2024.(ix)

Enter the trees. Tree canopy can provide shade to cool an area by up to 10°F.(x) Increased tree canopy also can increase health equity and reduce air pollution, including carbon dioxide and particulates; reduce storm water runoff; provide food and habitat for wildlife; and provide economic benefits.(xi) As cited in a Kinder Institute study, “in 2015, the U.S. Forest Service estimated that Houston’s urban forest reduces residential energy costs by $53.9 million and runoff by $7.8 million per year. The overall estimated compensatory value of Houston's trees was estimated at $16.3 billion.” Also, as clearly illustrated in the graphic, that coverage is not equal across the region.(xii) Importantly, as Sierra Club members know, greenspaces and trees also improve our sense of well-being.

Dr. Stephanie Piper of HARC, who led the 2024 heat mapping study and is leading response efforts under the related grant from the US Department of Agriculture Forest Service, noted that the program plans to plant, water, and maintain 54,310 trees over the 5-year grant period. In a June 2025 email, Dr. Piper noted that, to date, the program has “given away or planted 3,206 trees representing 31 species. Most are shade trees, but also includes fruit/nut, ornamental, and evergreen trees.” HARC coordinates with partners like the Student Conservation Association and American Youth Works to engage young people in career-building areas, including data science, work crews, trail maintenance, and tree planting. HARC also coordinates with Harris County Precinct leaders, especially in precincts that have the largest urban heat impacts, on planning locations for cooling centers and plantings based on the study’s data.

Some recommendations for a successful tree planting project include: design to establish a varied and well-structured high-quality canopy, as well as for total coverage; use a variety of tree species based on size at maturity to create a healthy well-structured and dense canopy, i.e., understory, subcanopy, and canopy layers; use a diverse mix of native tree species selected to maximize reductions in heat. Watering and maintenance are critical success factors. In addition, it’s critical to engage community groups from the outset.(xiii)

Many organizations are active in planting and maintaining trees in the Houston area. The City of Houston set a goal of adding 4.6 million new trees by 2030. In 2023-24, Trees for Houston planted 36,277 trees in public green spaces, planted 42 local Houston parks, and planted 3,577 trees at 59 local schools.(xiv)

Building out urban forests and green spaces is one of the approaches proven to ameliorate the urban heat effect. Besides critical efforts to slow down and reduce the impacts of climate change and of expanded development, other approaches to addressing urban heat include using “cool roofs” and heat-reflective materials for buildings and roadways. In addition, the City of Houston and Harris County maintain programs to provide residents with access to cooling centers on the hottest days.(xv)

Notes:

  1. Houston Climate Impact Assessment 2.0 Understanding Houston's Past and Future Climate and What it Means for You, prepared for the City of Houston, May 27, 2022, “Urban & Extreme Heat,” https://storymaps.arcgis.com/stories/ab02f9edd0904f3f83fbf080f41ad3f6
  2. Houston Harris Heat Action Team, 2020 Campaign Results, https://www.h3at.org/2020-campaign/2020-campaign-results . This study confirmed and expanded the results of a similar, but smaller, study in 2020.
  3. Cooling Houston with Community Science, Houston Harris Heat Action Team (H3AT), Houston Advanced Research Center (HARC), February 19, 2025, “Key Takeaways,” https://storymaps.arcgis.com/stories/1a2868e1573344d6bad0dc30effbee6f
  4. Ibid., “Urban Heat Island,” https://storymaps.arcgis.com/stories/1a2868e1573344d6bad0dc30effbee6f . Data from the 2020 and 2024 studies are available as open data sets to researchers and help to inform planning for locations and types of remediations.
  5. Health Impacts of Excessive Heat in Harris County, TX 2024, Harris County Public Health, 2024, p.6
  6. A Case for Cool Trees: Advancing Houston’s Tree Equity, HARC, 2024, p.3, https://harcresearch.org/wp-content/uploads/2024/01/A-Case-for-Cool-Trees-Report-FINAL.pdf
  7. Ibid., Health Impacts, p.23
  8. Ibid., Cooling Houston with Community Science, “Houston Hot Spots,” https://storymaps.arcgis.com/stories/1a2868e1573344d6bad0dc30effbee6f
  9. The Importance of Houston's Future Tree Canopy, Frank Blake, Sierra Club, May 27, 2024, https://www.sierraclub.org/texas/houston/blog/2024/05/importance-houston-s-future-tree-canopy
  10. Ibid., Cooling Houston with Community Science, “Cooling an Urban Heat Island,” https://storymaps.arcgis.com/stories/1a2868e1573344d6bad0dc30effbee6f
  11. Ibid., A Case for Cool Trees, p.4. Tree canopy cover prevents deaths and heat-related doctor visits, providing an estimated $1.3 to $2.9 billion value annually.
  12. Harris County appears to be losing more trees than it is planting. New datasets explore which neighborhoods lost the most, Rice University, Kinder Institute for Urban Research, April 11, 2024,https://kinder.rice.edu/urbanedge/harris-county-losing-more-trees-new-datasets
  13. Ibid., A Case for Cool Trees, pp.7-13
  14. https://www.treesforhouston.org/our-mission Cooling Centers, https://storymaps.arcgis.com/stories/c2bd3a645a404df49732881307c18c1e