How America's hottest city is trying to cool down

Can trees help save Phoenix from extreme heat?

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It’s time to stop looking at trees as a form of “beautification.” They are, instead, a living form of infrastructure, providing a variety of services that include stormwater management, air filtering, carbon sequestration, and, most importantly for a city like Phoenix, Arizona, they cool the environment around them.

Trees can lower neighborhood temperatures in three ways:
1) Their shade prevents solar radiation from hitting paved surfaces like concrete and asphalt, which absorb energy and rerelease it into the air as heat.
2) Their leaves pull heat from the immediate area in order to evapotranspirate water that’s drawn from the soil.
And, 3) If you’re standing under one, a tree protects your body directly from the sun’s rays. If you’ve ever made a summer visit to a dry, hot city like Phoenix, you’ll know how important shade is for making any outdoor experiences tolerable.

As Phoenix deals with a rising frequency of extreme heat waves — which aren’t only deadly, but also cause worrisome spikes in energy demand — the city is looking to trees as part of its heat mitigation strategy. Phoenix isn’t devoid of trees, but they’re distributed unevenly across the city. A quick glance at a satellite image of the metro area reveals substantial green splotches in the north and east and brown ones in the south and west, where many lower-income neighborhoods are located.

So Phoenix recently pledged to reach “tree equity” by 2030, under an agreement with American Forests, a national tree organization. I visited Phoenix recently to take a look at the current state of the city’s urban forest. In this video, we use drone imagery and thermal cameras to understand how the urban design of the city contributes to extreme heat, and what it can do to cool down.

This is the first video of five videos we're releasing on climate change. You can watch the second video, about high-voltage transmission lines ⚡️ and why the US isn't ready for clean energy, here: https://youtu.be/s3ScJ_FwaZk

And the third video dives into prescribed burns, and how a decade of suppressing forest fires ? may have made them worse, here: https://youtu.be/0o6ezu_h6iE

Further reading:

Tree Equity Score Tool by American Forests https://treeequityscore.org

Assessment of heat mitigation strategies in Phoenix by Arizona State University https://www.phoenix.gov/parkssite/Documents/PKS_Forestry/PKS_Forestry_NOAA_PHX_Urban_Spaces_Report.pdf

Urban Heat Implications from Parking, Roads, and Cars https://par.nsf.gov/servlets/purl/10201112

“Phoenix pledges tree equity for all neighborhoods by 2030” by KJZZ https://kjzz.org/content/1677263/phoenix-pledges-tree-equity-all-neighborhoods-2030

Phoenix Draft Climate Action Plan: https://www.phoenix.gov/oep/cap

Phoenix tree bank https://www.phoenix.gov/sustainability/plantatree

“50 Grades of Shade” by Ariane Middel https://journals.ametsoc.org/view/journals/bams/aop/BAMS-D-20-0193.1/BAMS-D-20-0193.1.xml

“A New Investigation About Who’s Getting Sick From Heat-Related Illness Should Be a Wakeup Call for America” by Mother Jones https://www.motherjones.com/environment/2021/01/a-new-investigation-about-who-is-dying-from-heat-related-illness-should-be-a-wakeup-call-for-america/

“As rising heat bakes US cities, the poor often feel it most” by NPR https://www.npr.org/2019/09/03/754044732/as-rising-heat-bakes-u-s-cities-the-poor-often-feel-it-most?t=1628079007286

“Can trees really cool our cities down?” by The Conversation https://theconversation.com/can-trees-really-cool-our-cities-down-44099

“Trees are key to fighting urban heat, but cities keep losing them” by NPR https://www.npr.org/2019/09/04/755349748/trees-are-key-to-fighting-urban-heat-but-cities-keep-losing-them

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