Tucson Arizona climate change trees

Planting a million trees in the semi-arid desert to combat climate change

Tucson's ambitious tree planting goal aims to improve the health of residents, wildlife, and the watershed.

Reflecting on her childhood, Tucson, Ariz., Mayor Regina Romero points to her father as the figure who lit an environmentalist fire within her.


Any chance he'd get, Romero's father would take his wife and six kids to an 800-acre ranch in the Sierra Madre mountain range of Sonora, where they learned how to ride horses, direct cattle, and to respect the wildlife, such as bobcats and brown bears.

"We invaded their space," he would tell them.

At the ranch, there was an outhouse instead of running water, rivers instead of showers. It was very rudimentary, Romero told EHN.

But riding through these biodiverse mountains on horseback made it all worth it.

"It was just so liberating," Romero said.

Five years ago, Romero's father passed away. Still his legacy lives on, as Romero, the first-ever Latina mayor of America's 33rd largest city, uses her platform to build an environmentally resilient community.

\u200bRegina Romero, mayor of Tucson, Arizona

Regina Romero, mayor of Tucson, Arizona. (Credit: Wikimedia Commons)

In Feb., Romero solidified a pledge to plant 1 million trees in the semi-arid desert city by 2030, when she joined the 1t.org US Chapter Stakeholder Council, a group of public, private and nonprofit leaders committed to the restoration of 1 trillion trees globally.

The U.S. chapter, including REI, National Forest Foundation, Amazon, the City of Dallas and the City of Tucson, have committed to more than 1 billion trees thus far.

Romero's goal: adapting to a rapidly changing climate in the country's third fastest warming city.

"Climate change waits for no one," Romero said. "Without a liveable community, we have no Tucson."

Currently, Tucson supports an estimated 1.6 million trees.

Low income neighborhoods hit hardest

Romero, urban forestry manager Nicole Gillet, and local groups such as Tucson Clean and Beautiful, are prioritizing tree-planting in low-income communities, which are disproportionately burdened by Tucson's urban heat island effect.

"We have to attack the problem where the problem exists," Romero said.

According to a Climate Central report, Tucson has warmed by 4.48 degrees Fahrenheit since the first Earth Day in 1970, which is more than Phoenix, 110 miles to the north.

Recent research shows that some Tucson neighborhoods are up to 8 degrees F warmer than the city's average. Neighborhoods with the highest Latino populations are 4 to 5 degrees F warmer on average.

"It's not that the heat is seeking out low-income populations," lead author, John Dialesandro, a Ph.D. candidate studying urban climatology at University of California, Davis, told EHN. "It's a lack of greenspace."

In the desert Southwest, the extra heat that low-income neighborhoods endure often coincides with lack of air conditioning. Many households must choose between air conditioning, healthcare, and food, one University of Arizona paper said.

These communities with less indoor cooling often have fewer trees to provide shade as well.

Some Tucson neighborhoods with high poverty rates are only 1 to 2 percent shaded by tree canopy, according to an American Forests tree equity map.

This is an issue of public health, Adriana Zuniga, an assistant research scientist in the University of Arizona's College of Architecture, Planning and Landscape Architecture, told EHN.

"It affects quality of life," Zuniga said. "Vegetation is linked to better air, lower temperatures, less stress, studies show less use of antidepressant medication."

Trees help biodiversity

arizona trees

2020 was Tucson's driest year on record, at only 4.17 total inches of rainfall. (Photo credit: Sean Benesh/Unsplash)

According to Zuniga, urban vegetation can also alleviate issues facing desert biodiversity, especially migratory species.

"Their habitats have been fragmented so much from urbanization that every spot of vegetation counts," Zuniga said.

Migratory pollinators are declining in the Sonoran Desert. More than 10,000 pollinator species are at risk in the Southwest, according to the Desert Botanical Garden in Phoenix.

The monarch butterfly, known for its remarkable blood-orange wings, is a keystone species that relies on nectar resources in southern Arizona during its spring migration.

Over the last two decades, monarch populations have fallen by 80 percent. Some of the causes include climate change, drought, deforestation and declines in milkweed plants, which female monarchs rely on for laying eggs.

"They desperately, desperately need our help in developing those patches of habitat for them to use while they migrate back and forth from Mexico, all the way to Canada," Zuniga said.

Restoring the watershed during a drought

Trees need water. And the Southwest is in a drought.

2020 was Tucson's driest year on record, at only 4.17 total inches of rainfall.

Thus, planting 1 million trees in the next decade has faced criticism.

But Lisa Shipek, executive director of Watershed Management Group in Tucson, believes that the initiative is realistic if native, drought-tolerant trees are planted.

"Velvet mesquite trees, desert ironwood, blue palo verde—there are a number of trees that are very appropriate to plant in the city, are found at these low elevations, and can be sustained just on rainwater," Shipek told EHN.

In fact, Shipek said, planting 1 million trees could actually restore parts of the Tucson watershed.

Before the mid-1900s, Tucson had a platter of perennially flowing rivers and creeks, such as the Santa Cruz River, Rillito River, and Sabino Creek. Then came over-pumping and massive urban development.

Now, it is rare to see flowing water.

In urban areas, where much of the surface is paved and impermeable, the million tree initiative could allow more rainfall to reach Tucson's watershed, according to Shipek.

"Putting in a rain basin with every single tree will help restore the watershed and ensure more water is infiltrated where the rain is falling," Shipek said.

A rain basin is a surface that allows rainwater to soak in and feed the trees, and indirectly, Tucson's groundwater. Groundwater contributes to streamflow.

Rainwater will be the primary fuel for the million trees initiative. When Romero entered office, she and her council approved a green stormwater infrastructure fee, which charges the average residential water-user $1 per month. Over the next three years, the fee will generate up to $7 million for sustainable stormwater harvesting in parks, streets, and parking lots, according to Romero.

Relying on rain in a drought is tricky, but according to Katie Gannon, program director at Tucson Clean and Beautiful, rain will reach these trees by way of nature. When more trees are present, the surrounding air becomes cooler, causing more clouds to drift into the low-pressure system, she told EHN.

"Green attracts rainfall," Gannon said.

Banner photo: Tucson, Arizona. (Credit: Manny Pacheco/flickr)

An economist's 'answer to everything.' Hint: It takes Nature

Economist Partha Dasgupta takes issue with our failure to account for the cost of Earth's destruction

Partha Dasgupta is a Cambridge University economist who has criticized politicians and economists for not including the cost of Earth's destruction when tallying things like economic growth.

This engaging video featuring Dasgupta and Danish actor Alexander Skarsgård boils his 600-page treatise down to five minutes.

Stanford University biologist Paul Ehrlich says "watching this is likely your mind's best use of five minutes this week."

The bottom line: We have to start accounting for Nature.

Not doing so, Skarsgård notes in the video, is like using only the goals your team scores to assess a soccer game. You might have an impressive number, but you have no idea if your team is winning or losing.

Worth your time....

Senator Whitehouse & climate change

Senator Whitehouse puts climate change on budget committee’s agenda

For more than a decade, Senator Sheldon Whitehouse gave daily warnings about the mounting threat of climate change. Now he has a powerful new perch.
tony reames energy department justice
Photo by Sara Cottle on Unsplash

Energy Department is serious about equity

"Equity and justice are central to everything that we do: As the U.S. Department of Energy’s deputy director for energy justice, Dr. Tony Reames helps to put equitable energy policy into action.

gas energy emissions climate europe
Photo by Théo Rué on Unsplash

EU approves 2035 ban on sales of gas-powered cars

EU countries have approved an end to the sale of gas-powered cars in 2035, allowing the law to enter into force.

columbia river salmon hatcheries
Photo by Jamie Pilgrim on Unsplash

Federal leaders finally increase money for hatcheries, but tribes say it’s nowhere near enough

The federal government has announced plans to increase funding for the Columbia River Basin’s salmon hatcheries, the often-crumbling facilities that maintain the river’s dwindling salmon populations. But tribes and state agencies say the influx of funds is only a fraction of what is needed.

european court of human rights climate lawsuits
Photo by Saúl Bucio on Unsplash

Climate fights at European court may ripple across the globe

Three climate lawsuits are making their way to a prominent court in France. Its rulings cannot be appealed and may have ripple effects in the United States.
climate kelp farming
Photo by Shane Stagner on Unsplash

Can we counter climate change by dumping carbon in the ocean?

Researchers and start-ups are exploring a variety of ways of locking up carbon in the sea, from seaweed farming to fertilising the oceans with iron – but we know little about the implications.

Brandon Moffatt: Climate Action 2.0 starts with certainty and access to capital green economy leaders

Climate Action 2.0 means acknowledging Canada is now in a competition with other advanced nations that are building their own foundations to attract the top talent of the green economy.

From our Newsroom
oil and gas wells pollution

What happens if the largest owner of oil and gas wells in the US goes bankrupt?

Diversified Energy’s liabilities exceed its assets, according to a new report, sparking concerns about whether taxpayers will wind up paying to plug its 70,000 wells.

Paul Ehrlich

Paul Ehrlich: A journey through science and politics

In his new book, the famous scientist reflects on an unparalleled career on our fascinating, ever-changing planet.

oil and gas california environmental justice

Will California’s new oil and gas laws protect people from toxic pollution?

California will soon have the largest oil drilling setbacks in the U.S. Experts say other states can learn from this move.

popular stories 2022

Our 5 most popular reads from 2022

A corpse, woodworking dangers, plastic titans ... revisit the stories that stuck with our readers this past year.

Stay informed: sign up for The Daily Climate newsletter
Top news on climate impacts, solutions, politics, drivers. Delivered to your inbox week days.