Las Vegas leaders are banking on trees for cooling: The science is complicated

As extreme heat claims more lives during ruthless summers in the region, Southern Nevada is upping the ante in its tree-planting efforts. But a new study suggests trees alone may not be enough to make a meaningful difference in the daytime.

While Las Vegas’ trees can cool surrounding air temperatures up to nearly 35 degrees at night and shade can cool people under trees, the study found that air temperature cooling is negligible, at best, during the day. It’s too hot for trees to release moisture via transpiration.

“When you measure air temperature, the cooling effect of trees is usually very, very low,” said Juan Henao Castaneda, a postdoctoral researcher at the Desert Research Institute (DRI) and the study’s lead author. “Reducing air temperature below one degree or two degrees is hard for any of the most common adaptation measures.”

Extreme heat, elevated by climate change, remains a chief concern and a worsening threat to Southern Nevada. More than 500 people died from heat-related causes last year, and heat-related emergency room visits jumped about 40 percent from 2023 to 2024. This summer has been mild by comparison.

The bottom line is that trees come with their own baggage as an extreme heat solution and shouldn’t be the only one urban planners implement, said John Mejia, a study author and DRI climatologist.

“They need a lot of care,” Mejia said. “They are expensive to take care of. In many other cities, they have had challenges in keeping trees alive, even in more humid and more friendly environments for trees.”

Trees still lifeline in nighttime

Long-term extreme heat response in Southern Nevada, while only a handful of years in the making, is mostly limited to bolstering tree canopy in the region’s most densely paved urban heat islands.

The city of Las Vegas aims to plant 60,000 trees by 2050. UNLV’s Las Vegas Urban Forest Center will put in 3,000 trees by 2028, and the nonprofit Impact NV is committed to planting 100,000 trees by 2032. Las Vegas has consistently ranked as the second-fastest warming city in the country in annual analyses by the nonprofit Climate Central.

Peter Ibsen, a U.S. Geological Survey research ecologist published a nationwide study last year that found Las Vegas could experience a cooling benefit from trees more than any other hot city in the country.

In an interview, he said the DRI study is a worthy addition to the conversation of urban forestry and extreme heat, though the study methods and findings were different. Careful consideration should be put behind where trees can reap the most benefit, and in which direction they should be planted for maximum shade, he said.

“Trees are one part of the heat mitigation toolkit,” Ibsen said. “Trees also do many other things. A shade structure will provide shade, but will it provide biodiversity habitat? Will it be aesthetically pleasing? We focus on heat, but it’s not easy to measure, and there’s many different ways we can approach this question.”

In the short term, Clark County’s cooling centers—usually a community center or library—open their doors when the National Weather Service issues an extreme heat warning.

The new study affirms that trees have never been a silver bullet to cool cities, said Ariel Choinard, coordinator of the Nevada Heat Lab, a Desert Research Institute research initiative formed in 2023 that directs heat mitigation efforts throughout the state.

She pointed to the nighttime cooling effect on air temperatures outlined in the study—an important piece of the equation as nights heat up in Las Vegas at an unprecedented rate. The cumulative effects of heat on the body when nights don’t provide cooling relief are often ignored, Choinard said.

“There’s an emotional reaction to hearing that trees weren’t the one weird trick to solve Las Vegas being one of the fastest warming cities in the nation,” Choinard said. “Trees are a solution. They are not the solution, but they will still provide people with incredible relief.”

Charting adaptation forward

Many trees may not survive climate change. A 2019 Southern Nevada Water Authority study found about 38% of the 100 most common plants used in landscape conversions won’t be able to withstand hot temperatures by 2055.

Some neighborhood groups, including the Water Fairness Coalition, have been critical of the water authority’s conservation programs, such as the removal of “nonfunctional turf” before 2027 as mandated by the Nevada Legislature.

Among their chief concerns are fewer green spaces and trees to cool off urban heat islands. Previously, the water authority said in an interview that trees are dying across the valley because of mismanagement on private property. The agency offers rebates for new trees planted on lawns converted to desert landscaping and tips for plant selection.

Choinard’s lab recently hired urban forestry expert Cayenne Engel, who said having any hyperlocal study is a benefit to better understanding the unique effect trees have on Las Vegas.

Trees are often a popular adaptation method to heat because people have an emotional and cultural connection to them, Engel said. When the study came out, Engel said community members reached out with many questions.

“The response is potentially surprising,” Engel said. “The results are that trees don’t significantly change the air temperature any more than built-environment shade; that makes sense when you dig a little bit into tree physiology. Trees here are working at night instead of during the day. The science of it does make sense, and the story is complicated.”

In no way does the study suggest that trees are not a valuable tool to protect individuals from extreme heat, Engel said.

Henao Castaneda and Mejia will continue to research different extreme heat adaptation measures, hopefully equipping city planners and decision-makers with data specific to Las Vegas. As required by Assembly Bill 96, every municipality with more than 100,000 residents must update their master plans to include extreme heat mitigation.

“The beauty of what we are doing is we are creating basic information to help guide policy in the future,” Mejia said.

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