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New research shows how more trees could cut ER visits in heatwaves


New research shows how more trees could cut ER visits in heatwaves

A team of heat experts known as Los Angeles Urban Cooling Collaborative calculated exactly how much of a difference low-tech solutions like trees and white paint could make in an overheating world.
May 22, 2024

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Talk of tackling climate change often seems to involve high-tech gadgets—electric cars, giant wind turbines, machines that suck carbon dioxide from the air, and futuristic air conditioners, among other things.

But sometimes, basic things can make the difference between life and death or sickness and health. Things like trees and some white paint.

Just ask scientists in Los Angeles who are studying ways to help keep people cool as the temperature rises. It turns out something as simple as planting more trees and increasing the amount of sunlight reflected from surfaces such as roofs could offer enough relief during a heatwave to cut the number of overheated people seeking help in hospital emergency rooms by as much as 50%. No need for futuristic technology.

“This is a key point,” the researchers write in the International Journal of Biometeorology.  “Present strategies exist to greatly improve public health during heat events.”

Heatwaves are among the most obvious and lethal effects of global warming. Cities, with their oceans of heat-absorbing asphalt and fewer trees, are literal hotpots. By one recent estimate, people in cities around the world today are experiencing deadly temperatures three times more than in the 1980s.

The toll is already being felt in LA. When a heatwave strikes there, deaths are estimated to rise 8% above what would normally be expected. Back-to-back extreme days have been linked to a 30% increase in deaths. The Los Angeles Times recently reported that roughly 3,900 Californians died from heat-related problems during heatwaves between 2010 and 2019.


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To see what might be done to help, a team of heat experts known as the Los Angeles Urban Cooling Collaborative looked at how much a difference could be made using low-tech solutions such as trees. That group includes researchers from the University of California Los Angeles, Kent State, Arizona State University and Climate Resolve, an LA-based nonprofit.

In an earlier study, the researchers found that a large expansion of trees and surfaces treated to be more reflective—such as roofs covered in white paint—could drop temperatures in parts of LA by as much as 3 degrees Celsius and cut heatwave deaths by as much as 25%. That equates to saving nearly two dozen people in a heatwave as severe as one that hit the city in September 2010.

In the new research, the scientists turned their attention to relieving medical problems that aren’t lethal. In some ways, that can be trickier to measure because illnesses aren’t tracked as closely by health care agencies as deaths. The scientists opted for using visits to LA county hospital emergency rooms as a surrogate for sickness. They gathered reams of data about these visits between 2005 and 2018. They then looked at how the ER patterns changed when the region was struck by 4 different heatwaves during that time.

Not surprisingly, the data revealed more ER visits as temperatures climbed, particularly for problems that can be exacerbated by heat. In the most severe heatwave, county hospitals got another 245 visits than would be expected in cooler conditions, with 145 of those coming from heat-related conditions, the researchers found.

To see what difference trees and paint might make, the scientists turned to a weather forecasting model created by a group of federal research agencies and the University of Oklahoma. In the digital version of LA, they tweaked the reflectiveness of surfaces and the amount of tree cover to see how that would influence local weather conditions. The most modest scenario had tree cover increase from the current 18% to 22.5%. The reflectivity, or albedo, increased by 75% to 100% for roofs and pavement. In the most ambitious future, the scientists envisioned trees shading 40% of the county and reflectivity doubling or even tripling for different kinds of infrastructure.

The scientists found that the scenario with the smallest increase in tree cover would have reduced ER visits by between eight and 49 people depending on the heatwave. By contrast, a big expansion in trees and white roofs and pavement would have meant between 19 and 85 fewer people going to the hospital—a drop of between 12% and 47%.

New trees tall enough to make meaningful shade don’t grow overnight. But the research suggests that starting now in places like L.A. could mean fewer trips to the hospital and to the morgue in a hotter future. That doesn’t require waiting for a fancy new invention. These options, as the scientists write, “are available and should be prioritized.”

Sheridan, et. al. “Increasing tree cover and high‑albedo surfaces reduces heat‑related ER visits in Los Angeles, CA.” International Journal of Biometeorology. April 29, 2024.

Image: ©Anthropocene Magazine, AI-generated

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