Re-posting this here from the Nerd Corner 🤓 There's a nice new study of urban trees in Los Angeles published in the International Journal of Biometeorology. The paper notes that during heatwaves, deaths in LA increase by 30% due to increased heat stress that can aggravate underlying health conditions. The worsening heat waves that result from global warming are especially dangerous in cities, which experience urban heat island effects from all the concrete and asphalt radiating heat and causing extra hot local temperatures.
But urban trees can play an important role in cooling those local temperatures by providing shade and 'evapotranspiration,' which is basically a release of water vapor from the leaves into the air. And painting roofs white and making pavement lighter colors (a.k.a. increasing their 'albedo', or reflectiveness) can also reflect more sunlight. These effects can cool local temperatures by something like 5°F, reducing heat-related deaths by over 25%.
This particular study looked at emergency room (ER) visits during four extreme heat events in LA between 2006 and 2010. In a scenario with a lot of urban trees and high albedo/reflectiveness, they estimated that the number of ER visits for all causes would have decreased by 12–47%, and specifically heat-related ER visits would decline by 26–66%. These measures would be especially effective in a very hot and dry heatwave as happened in LA in 2010, and somewhat less effective in a humid heatwave, like the 'moist tropical (MT)' event that happened there in 2006.
As the study concluded, urban trees are awesome 🌳:Â
Strategic changes in the land cover of urban areas can have significant and measurable positive benefits for public health, particularly for lower-income communities and people of color who suffer disproportionately from heat.
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