Cooling Houston with Community Science

Houston hosted the largest single day heat mapping campaign in U.S. history! The data, collected by over 150 community members, shows that heat varies throughout Houston with a maximum difference of 14˚F between neighborhoods. Neighborhoods can be hotspots, a maximum temperature of 103˚F was measured in Hidden Valley, a neighborhood located near the intersection of I-45 and 249. One of the largest continuous areas facing multiple indicators of high heat stress is in the southwest portion of the City of Houston, which includes Gulfton, Alief, Sharpstown, Westwood, and Mid West.

Scroll through this StoryMap to explore hotspots, how heat varies, and how we can create a cooler Houston. 

Harris County, home to Houston, is no stranger to hot weather. However, there are communities within Harris County that are warmer than others. In part, this is caused by the “Urban Heat Island Effect.” Buildings, roads, and other man-made structures absorb the sun's heat during the day and release it as radiant heat. These areas are hotter than natural landscapes like forests, which stay cooler by providing shade and absorbing less heat. Since cities often have fewer trees and other plants to keep things cool, they become "heat islands" - EPA ( Heat Island Effect | US EPA)  

High temperatures mean potentially more heat stress related impacts. From 2019-2023, Harris County Public Health found an increase in heat related illness encounters, shown below. The Houston Harris Heat Action Team (H3AT)  mapped heat in 2020 , but with increased heat risk, it is important to continue identifying hotspots. 

Houston regularly faces high heat in the summer months, which can put residents at risk. Heat-related illness is particularly harmful to those who have existing health concerns or are vulnerable, many of whom live in under-resourced communities. Identifying high risk heat areas as well as potential solutions to address soaring temperatures is crucial to reduce potential impacts in our communities. 

Afternoon temperature represents maximum heat exposure because heat is highest during this time of day. While this data is a snapshot of one hot summer day in August, it provides insight into a possible range of temperatures. The afternoon temperature averaged across the full campaign area was 94°F. Areas in red show where higher heat was present, with a maximum observed temperature of 103°F.

Keep scrolling to learn more about what we learned from the 2024 heat campaign results. 

The heat anomaly identification compares the afternoon (3 to 4 PM) average temperature of each neighborhood to the overall study area average to identify hotspots. This identifies hot spots within Houston and Harris County neighborhoods on campaign day. The darkest colored areas are hotter than the average observed temperature. Areas in deep maroon were above average and hotter, while areas in beige were below the average temperature.

One way to identify heat hotspots is by exploring the maximum afternoon temperatures between the hottest and coolest areas. This can be done by comparing the top 10% of locations with the highest temperatures, in orange, to the bottom 10% with the lowest temperatures, in purple. This map reveals the makings of Houston’s distinctive urban heat island pattern.  

In Houston, the neighborhoods with the highest maximum afternoon temperatures—the top 10%—include Gulfton, Alief, Sharpstown, and Sunnyside, among others. These communities face more heat, which can impact residents’ comfort, health, and energy costs. In other parts of the city, some areas remain significantly cooler. Areas such as Baytown, La Porte, Tomball, and Northside/Northline rank in the bottom 10% for maximum afternoon temperatures, providing a bit of relief from the heat. 

The hottest areas are in Houston's urban core, where generally there is less greenspace and denser development. These hotspots are influenced by buildings that trap heat and block natural airflow, as well as vehicles, air conditioners, and industrial facilities that generate both heat and pollution. A lack of trees and plants (which naturally cool the air by providing shade and releasing moisture) and high amounts of dark surfaces that absorb heat (like asphalt and concrete) further worsen the warm conditions.

Morning temperatures are typically the lowest after hours of nighttime cooling. Urban areas reaching morning temperatures over 80°F are more likely to face extreme heat later in the day. This map represents the morning temperature difference, measured from 6-7 AM, compared to the 80°F threshold. Dark purple areas show where there are higher morning temperatures which can be nearly 7°F hotter than other neighborhoods. 

The nighttime temperature map shows the difference between morning and evening temperatures. When the difference between the two measurements is small, it means that area does not benefit from overnight cooling. Overnight cooling provides relief from high temperatures. Developed areas have higher amounts of surfaces like asphalt or cement that absorb and trap heat even at night. 

The evening temperature model shows that while some areas are cooled, other neighborhoods remained hot. Some areas experience nighttime temperatures within just 10 degrees of the maximum afternoon temperature observed in those same areas. 

Heat waves kill more people than any other extreme weather event in the US. Nationwide heat-related deaths and ambulance dispatches due to heat reached record highs in 2023 ( Source: PBS ). In Texas, over 300 people died from heat-related causes in 2023 ( Source: Texas Tribune ). Extreme heat risks, like dehydration, heat exhaustion, and heat stroke, are a major health issue that Houstonians face.  

Risks from heat are compounded in communities that are already vulnerable such as places where residents cannot afford air conditioning or areas lack cooling from green space. Several chronic diseases that are more prevalent in older populations are exacerbated by heat. Older homes without insulation are difficult and expensive to cool, adding a burden on low-income families. Certain groups, including older adults, outside workers, children, and people with disabilities or chronic health conditions, like heart disease, respiratory disease, and diabetes, are more vulnerable to extreme heat. With increasing danger, understanding heat is important to keep residents healthy and safe.

For more information, read about Harris County Public Health’s  heat vulnerability index . HCPH assigns a score to each location, and a higher score indicates that the community is more vulnerable than those around them. 

Reducing the health impacts of extreme heat exposure is essential to protecting vulnerable residents. But how can we begin to cool urban heat islands? What sustainable solutions exist that are practical and will benefit communities and support biodiversity? Trees!

As trees grow, so does their canopy, which provides cooling shade to people, homes, and buildings. Trees also provide habitat for birds and other wildlife. Tree canopy can provide shade to cool an area by up to 10°F ( Ziter et al, 2019 ). Other cooling interventions may include cool pavements, green roofs, and native prairie plantings!  

There are currently many efforts underway to increase Houston’s tree canopy. Through the ForUsTree project, a landmark, five-year, community forestry initiative to improve tree canopy equity, build resilience, and create green employment opportunities, over 54,000 trees will be planted. 

Learn more at  forustreehtx.org !