Introduction to the Problem
The vast majority of urban, public grade schools in California are paved-over “nature deserts” sorely lacking in trees or shade — leaving most of the state’s 5.8 million school-age children to bake in the sun during breaks from the classroom as rising global temperatures usher in more dangerous heat waves.
Research Findings
That’s the conclusion of a team of California researchers from UCLA, UC Davis and UC Berkeley who studied changes in the tree cover at 7,262 urban public schools across the Golden State between 2018 through 2022. The ongoing joint project, which drew from urban tree canopy maps developed by study partners the California Department of Forestry and Fire Protection and the U.S. Forest Service, revealed that 85% of the schools lost about 1.8% of tree cover on average in that four-year span.
Tree Cover and Shade
The researchers also collaborated with the nonprofit Green Schoolyards America, which found in its own 2024 study that California’s public K-12 schoolyards have a median tree cover of just 6.4%. And more than half of that canopy exists only as decoration at school entrances, in parking lots and along campus perimeters. “Extreme heat is becoming a major public health concern in California and across the country, and trees can play a really big role in helping us cool down those schools and also build climate resilience,” said Kirsten Schwarz, the research lead at UCLA.
Impact of Heat on Students
Results from the 2018 to 2022 study, which was funded by the U.S. Forest Service, were recently published in the journal Urban Forestry and Urban Planning. Children also haven’t fully developed the ability to regulate their body temperature the way adults can, making them more vulnerable to extreme heat and potentially hindering their ability to learn. In addition, for children who live in places without grass or safe parks and playgrounds, school might be the one place where they can experience cooling outdoor environments and unpaved surfaces.
Variations Across Districts
While 15% of the schools surveyed saw gains in tree cover thanks in part to schoolyard greening projects — particularly in the Central Valley, around Sacramento and in Imperial County — many individual schools surveyed experienced big losses in net tree cover in that time. In some cases, those added up to more than 40%. Among the state’s largest school districts, San Francisco had the greatest canopy loss, 16.3%. On the other end of the spectrum, Sacramento had the greatest gain at 7.5%, followed by Long Beach, which saw a 4% canopy increase.
Challenges and Solutions
Schools in Los Angeles showed a small net loss of 0.5%. The researchers cautioned not to read too much into that modest figure, because longstanding disparities in tree cover and shade across the city still expose schools in poorer neighborhoods away from the ocean to greater sun and intense outdoor heat than schools that benefit from their proximity to cooling ocean breezes and lingering marine cloud cover. There are many obstacles to making campuses more hospitable. Schwarz cited a 2024 policy report by her UCLA team that examined the greening of inadequately shaded schools and policies that make it difficult to carry out improvements.
Overcoming Barriers
Other schools have to choose between conflicting long-term priorities, the student report said: Plans for the future construction of additional classrooms to accommodate growing student enrollments can outweigh the desire to create shadier open spaces. The tree canopy researchers plan to present each participating school with a tree inventory, analysis of findings, policy recommendations and suggestions for incorporating their study into classroom lessons and parent outreach. The researchers said their main motivation in initiating the study was to help communities get the most from $150 million in Cal Fire grants approved by the state Legislature that schools can apply for to plant grass and trees on their campuses and reduce the harm of heat-radiating surfaces such as asphalt.
Conclusion
The situation appears to be just as worrisome today, the team said. Ossola said that in some ways, Californians who want to improve their children’s schoolyards are playing catchup even with community will and funding sources in place. It can take decades for young trees planted today to mature enough to provide the necessary cooling effects that can make children safer on a warming planet. “This is a critical investment that we should’ve done 20 or 50 years ago,” Ossola said. “Now we’re kind of missing the bus.” The overarching goal is, how can we maximize these investments that we’re making in school greening?
FAQs
- Q: What percentage of California’s public K-12 schoolyards have a median tree cover?
A: 6.4% - Q: How many schools were studied in the research project?
A: 7,262 urban public schools - Q: What is the main goal of the researchers in initiating the study?
A: To help communities get the most from $150 million in Cal Fire grants to plant grass and trees on school campuses and reduce heat-radiating surfaces. - Q: Why are children more vulnerable to extreme heat?
A: Because they haven’t fully developed the ability to regulate their body temperature the way adults can. - Q: What can be done to improve the situation?
A: Schools can apply for grants to plant trees, reduce paved areas, and incorporate greening into their policies and classroom lessons.
