Are Trees the Key to Protecting Vulnerable Neighborhoods?

Targeted cooling strategies reveal trees as the ideal solution for Houston’s most heat-stressed neighborhoods.

Growing up, I loved watching nature documentaries. Since I couldn’t travel yet, and my parents couldn’t afford exotic trips during our vacations, this was my way of immersing myself in all corners of the world.

While my favorites were those about the African savannah or sharks, tropical rainforest documentaries had a third place in my heart. I listened carefully to everything the explorers had to say, fascinated by how they narrated their experiences.

I was specially intrigued to hear that they were sometimes cold in the rainforest, despite being in a tropical country. But I soon understood why.

My family loved hiking, and we often embarked in little adventures getting on top of mountains or crossing exuberant forests. One of the trails we were following took us inside a specially dense forest in a valley where a creek ran through.

As we entered this landscape, all my senses were activated. The smells were different; I could hear many more birds, insects, and frogs; it felt humid and… cold. It was the peak of the summer, and we had been sweating for most of the trail. But inside this little microniche of dense forest cover, it felt so cold that I got goosebumps.

Interesting, I thought. ‘This must be what it feels like to be in a rainforest,’ I told my mother, who looked puzzled but could see where I was coming from.

Indeed, trees have many superpowers, and their cooling effect could be a solution to protect neighborhoods within our cities, especially those that are more vulnerable. Let’s see what science has to say about this!

As climate change intensifies, cities worldwide grapple with hotter summers, but the heat isn’t felt equally across communities. In places like Houston, Texas, some neighborhoods are hit harder than others due to unique social and environmental conditions. An issue within the realm of environmental justice.

To address this uneven impact, a team from the University of Texas at Austin, along with collaborators in Spain and Canada, has developed a cutting-edge model that considers not just the physical heat but also social vulnerability.

Their work, recently published in PNAS Nexus, shows how different cooling strategies affect communities with varying needs and highlights that, in some of Houston’s most vulnerable areas, trees might be the best way to beat the heat. Yes, you hear that right, ‘just’ the all-mighty trees.

In their study, the team used advanced climate modeling to assess cooling strategies, including reflective roofs (known as cool roofs), green roofs, and tree planting, across different neighborhoods in Houston. They enhanced the Weather Research and Forecasting (WRF) model to capture how each method affects the “Universal Thermal Climate Index” (UTCI), which estimates how comfortable people feel outdoors.

But unlike many models, this one didn’t stop at climate science. By adding data on social vulnerability, like income levels and housing type, the researchers could assess which neighborhoods would benefit most from each cooling method. The ultimate design for cross-disciplinary research.

Dr. Kwun Yip Fung, the lead author, highlights the importance of understanding vulnerability: “Now that we have developed the index of cooling and we have the vulnerability data, if we combine both of them, we can see which methods provide more cooling for those vulnerable neighborhoods.”

Let’s backtrack a bit here. Houston is no stranger to the urban heat island effect, where buildings and roads trap more heat than natural landscapes, resulting in a city that’s warmer than its rural surroundings. The researchers found that reflective roofs, while highly effective at cooling during the day, aren’t as impactful in areas where they’re most needed.

In fact, in Houston’s low-income neighborhoods, trees proved to be the better choice for reducing heat stress. These areas tend to have fewer roofs suitable for reflective treatments, so tree planting can take advantage of available space, like sidewalks and vacant lots, where trees can provide shade and lower temperatures through a natural process called evapotranspiration.

As study co-author Dr. Zong-Liang Yang notes, “If construction workers work under direct sunlight versus under the shade of tree cover, the comfort level will be very different.”

The researchers also applied the CDC’s Social Vulnerability Index (SVI), which scores neighborhoods on factors like socioeconomic status and housing stability, allowing them to pinpoint which communities face the greatest risks.

When combining the SVI with the UTCI, it became clear that trees, by cooling surrounding air and blocking sunlight, offer unique benefits to these vulnerable areas that other methods like reflective or green roofs cannot.

But what do these results mean to the rest of the world?

The modeling results showed that although cool roofs performed slightly better for immediate temperature reductions across the entire city, trees offered the best cooling in Houston’s most vulnerable neighborhoods.

With a 0.27-degree Celsius cooling effect, trees might not seem like game-changers, but for areas experiencing extreme heat regularly, this can be a significant improvement. According to Dr. Fung, “The research revealed that places with high vulnerabilities also had more available space where trees could be planted, so the potential for adding trees was greater.”

This makes implementation easy, indeed.

In contrast, reflective roofs, which work by bouncing sunlight back into the atmosphere, saw their effectiveness drop in neighborhoods with higher vulnerability scores. These areas had fewer large rooftops suitable for reflective materials or green roofs, which means they wouldn’t experience as much cooling as wealthier areas might with these solutions.

The findings suggest that tree planting should be prioritized for communities with high social vulnerability, while other neighborhoods can benefit from rooftop solutions, depending on their layout and needs. Indeed, we don’t need to choose one or the other; we just need to be aware of how effective each is.

But what’s the big picture here? And what does this mean for cities facing hotter summers each year?

This research offers a flexible approach to cooling that could help policymakers make better decisions about where to invest in heat-mitigation efforts. But this could be a solution that comes with many side benefits, too.

Trees don’t just cool neighborhoods — they also improve air quality, provide shade, and offer aesthetic and ecological value, making them a multipurpose asset for urban planning. On top of that, in Houston, planting trees in vulnerable neighborhoods could be the first step toward creating safer and more resilient communities in the face of rising temperatures.

A relatively cheap solution for a growing, more expensive issue.

However, the team’s model isn’t a one-size-fits-all solution. While trees might be ideal for humid climates, desert cities might need different species or entirely different solutions, such as combining trees with reflective pavements.

According to Dr. Fung, “Now that the index and the methodology have been developed, they can be applied to many other scenarios.” As urban areas around the world rethink their approach to cooling, models like this one can guide future strategies to ensure that every community, especially the most vulnerable, can stay safe and comfortable during heat waves.

It proves that we don’t need big budgets to make a difference.

This study emphasizes the importance of targeted, community-specific solutions for urban heat mitigation, reminding us that cooling the city isn’t just about temperature — it’s about equity and resilience.