New Student Paper - Heat in Public Parks

UC IRVINE PRESS RELEASE - A new study funded by a NASA grant awarded to the University of California, Irvine’s Joe C. Wen School of Population & Public Health has found that public parks in underserved areas of Los Angeles can reach dangerously high temperatures, in some cases hot enough to cause pain or burns, because of the materials used to build them.

The differences stem largely from what parks are made of. Researchers discovered that parks in South Los Angeles contain significantly more heat-retaining materials – such as artificial turf, concrete and rubber – while parks in West Los Angeles are far more likely to feature natural turf and vegetation.

The research, published recently in npj Urban Sustainability, a journal in the Nature Portfolio, analyzed park temperatures across Los Angeles County using satellite data from Ecostress, a thermal imaging experiment aboard the International Space Station. The results show stark temperature differences between parks in South Los Angeles and those in West Los Angeles, revealing how urban design and historical investment patterns shape exposure to extreme heat.

The study, conducted with collaborators from Chapman University and Tennessee State University, found that parks and open spaces in South Los Angeles averaged 105.8 degrees Fahrenheit during summer daytime conditions, compared with about 91.6 degrees Fahrenheit in West Los Angeles. More than a third of parks and recreational spaces in South Los Angeles reached or exceeded the surface temperature associated with the human pain threshold. No parks in West Los Angeles reached that point.

“Parks are often thought of as cooling refuges during extreme heat,” said Jason A. Douglas, associate professor and vice chair in Wen Public Health’s Department of Health, Society & Behavior. “But in some underserved communities, the parks that should provide relief are actually exposing residents to dangerous levels of heat.”

Natural surfaces, such as those more featured in West Los Angeles parks, help cool the environment through shade and evapotranspiration, the process by which plants release moisture into the air. Artificial materials absorb and retain heat.
The research also found stark differences in access to green space. Using a per capita measure to account for differences in study area size, West Los Angeles has 117.1 hectares of parkland per capita, compared to 9.1 in South Los Angeles.

“Residents in South Los Angeles face a double burden,” said Joshua Fisher, an associate professor of environmental science at Chapman University’s Schmid College of Science and Technology. “They have less access to parks, and the parks that do exist are often built with materials that trap heat instead of cooling the environment.”

The work used satellite observations collected between 2021 and 2024 to measure land surface temperatures at hundreds of parks and recreational areas, including schoolyards, playgrounds and open spaces. Employing machine-learning techniques, the team increased the resolution of the satellite data to analyze temperature differences across specific surfaces, such as grass, artificial turf and pavement.

The project was shaped in part by community concerns. Residents working with the environmental justice organization Communities for a Better Environment reported extremely hot park surfaces during community workshops and heat pocket mapping sessions. Some said that artificial-turf fields and playgrounds were hot enough to burn bare feet during summer months.

Those experiences prompted the research team to investigate whether the thermal conditions described could be measured across many parks using large-scale data, such as satellite observations.

Extreme heat is the deadliest weather-related hazard in the United States, and urban heat islands – built infrastructure that absorbs and traps heat disproportionately – tend to affect lower-income communities and people of color.

The study’s authors said the findings highlight how decades of unequal investment in urban infrastructure continue to shape environmental conditions and public health risks in cities.
 “Parks should be part of the solution to extreme heat,” Douglas said. “But the design and materials used in these spaces matter. If we want parks to protect communities during hotter summers, we need to invest in vegetation, shade and natural surfaces that actually cool the environment.”

The study was led by Ashley Agatep, an undergraduate researcher at Chapman University. Besides Douglas and Fisher, co-authors include Kainani Tacazon of Chapman University, Reginald Archer of Tennessee State University, Ambar Rivera and Rossmery Zayas from Communities for a Better Environment, and graduate student Juan Carlos Ruiz Malagon of UC Irvine.

This work was supported by NASA through its Equity and Environmental Justice Program and Ecostress Science and Applications Team.

The researchers said their findings could help inform future urban planning and park development strategies aimed at reducing heat exposure in vulnerable communities. As climate change drives more frequent and intense heat waves across Southern California, they said, ensuring equitable access to effective cooling infrastructure will be critical for protecting public health.