Street trees are effective in combating the heat, but the situation is different in the desert

On a hot day, it feels cool to be in the shade of a street tree. However, the situation seems to be different in areas surrounded by deserts. A research team from the Desert Research Institute (DRI) in the United States analyzed the effects of street trees in desert areas and summarized them in a paper.

Effectiveness of street trees in reducing air temperature and outdoor heat exposure in Las Vegas - IOPscience
https://iopscience.iop.org/article/10.1088/2752-5295/ade17d

A New, Detailed Analysis of the Benefits and Trade-offs of Urban Street Trees in Las Vegas - DRI
https://www.dri.edu/a-new-detailed-analysis-of-the-benefits-and-trade-offs-of-urban-street-trees-in-las-vegas/

In addition to providing shade, roadside trees and other plants also have the effect of lowering the temperature by absorbing heat from the surrounding area when they release water vapor from their leaves (transpiration). Using plants to lower the temperature is quite effective in water-rich areas such as Japan, and an increasing number of homes are incorporating ' green curtains' by growing plants such as bitter melon and morning glory outside their windows to achieve a cooling effect.

However, in desert areas, there are problems such as 'there are few plants that grow naturally in areas far from natural water sources' and 'the need to grow plants while conserving precious water.' Therefore, the research team of the Desert Institute analyzed whether the cooling effect of roadside trees is effective in the desert using computer simulations.

The research team chose Las Vegas as the area for the simulation. Many people have the image of Las Vegas as a 'resort with casinos,' but if you check the satellite image of the area around Las Vegas on Google Maps, you can see that it is surrounded by the vast Mojave Desert.


After calculating the effect of planting different types of street trees in various parts of Las Vegas on temperatures, they found that planting street trees could reduce nighttime temperatures by 1 degree, but did little to reduce daytime temperatures. They also found that cherry trees have three times the cooling effect of oak trees, but they also require three times as much water.

'Trees provide a lot of shade and help store carbon, but they also need a lot of water to cool the air,' said Juan Heona, a member of the research team. 'In a hot, dry city like Las Vegas, we need to be aware of the trade-offs and identify the right tree species to plant along our streets.'