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  • Writer's pictureWorld Half Full

Green corridors helping cool Medellín


It’s mid-afternoon along Medellín’s Avenida Oriental, a traffic-clogged street that slices through the heart of Colombia’s second largest city, and Nicolas Pineda is crouched down as cars zoom by on both sides. Wrapped up in heavy-duty workwear and armed with a machete, he’s weeding a thick strip of tree-lined greenery running between the lanes. He hacks at a patch of dead, browning bush and then pulls up a rogue, zig zag-shaped shrub beside his foot.

“Es bien bonita,” grins the 54-year-old, evidently pleased with his handiwork. “It’s very clean. That’s what I like to see: a clean, green city.”

Pineda has helped sow and maintain hundreds of thousands of trees and plants across Medellín (pop. 2.5 million) as part of a people-led project to reduce extreme heat through a network of “Green Corridors” across the city.

As Medellín has grown rapidly over the past few decades, so has the urban heat island effect, increasing temperatures in the city well above those in the surrounding suburban and rural areas. Roads and other concrete infrastructure absorb and maintain the sun’s heat for much longer, keeping the city hot for longer too. However, the City of Eternal Spring — Medellín’s nickname thanks to its year-round temperate climate — has found a way to keep its cool.

“Medellín grew at the expense of green spaces and vegetation,” says Pilar Vargas, a forest engineer working for City Hall. “We built and built and built. There wasn’t a lot of thought about the impact on the climate. It became obvious that had to change.”

Efforts began in 2016 under Medellín’s then mayor, Federico Gutiérrez, who after completing one term in 2019, was re-elected at the end of 2023. The city launched a new approach to its urban development — one that focused on people and plants.

The US$16.3 million initiative saw 30 Green Corridors added along the city’s roads and waterways, improving or producing more than 70 hectares of green space, which includes 20 kms of shaded routes with cycle lanes and pedestrian paths.

These plant and tree-filled spaces — which connect all sorts of green areas such as squares, parks, vertical gardens, footpaths, and even some of the seven hills that surround the city — produce fresh, cooling air in the face of urban heat. The corridors are also designed to mimic a natural forest with low, medium and tall plants, including native plants, bamboo grasses and palm trees.

Heat-trapping infrastructure such as metro rail stations and bridges has also been greened as part of the project and government buildings have been adorned with green roofs and vertical gardens. The first of those was installed at Medellín’s City Hall, where nearly 100,000 plants and 12 species span the 1,810-square-metre surface.

“It’s like urban acupuncture,” says Paula Zapata, advisor for Medellín at C40 Cities, a global network of about 100 of the world’s leading mayors. “The city is making these small interventions that together act to make a big impact.”

At the launch of the project, 120,000 individual plants and 12,500 trees were added to roads and parks across the city. By 2021, the figure had grown to 2.5 million plants and 880,000 trees. Each has been carefully chosen to maximise their impact.

“The technical team thought a lot about the species used. They selected endemic ones that have a functional use,” Zapata explains.

The 72 species chosen provide food for wildlife, help biodiversity spread and ease air pollution. One study, for example, identified Mangifera indica (mango) as the best among six species found in Medellín at absorbing PM2.5 pollution — particulate matter that can cause asthma, bronchitis and heart disease — and at surviving in polluted areas due to its “biochemical and biological mechanisms”.

And the urban planting continues to this day. The groundwork is carried out by 150 citizen-gardeners such as Pineda, who come from disadvantaged and minority backgrounds, with the support of 15 specialised forest engineers. He is now the leader of a team of seven gardeners who attend to various corridors across the city.

One of them is 40-year-old Victoria Perez, who like all of the other gardeners in the Green Corridors project, received training by experts from Medellín’s Joaquin Antonio Uribe Botanical Garden. “I’m completely in favour of the corridors,” says Perez, who grew up in a poor suburb. “It really improves the quality of life here.”

Wilmar Jesus, a 48-year-old Afro-Colombian farmer on his first day at work, is pleased about the project’s possibilities for his own future. “I want to learn more and become better,” he says. “This gives me the opportunity to advance myself.”

In the first three years of the project, Medellín’s temperatures fell by 2°C , and officials expect a further decrease of 4–5°C over the next few decades. In turn, City Hall says this will minimise the need for energy-intensive airconditioning.

And it’s having a dramatic effect on air pollution, too. Between 2016 and 2019, the level of PM2.5 fell significantly, and in turn the city’s morbidity rate from acute respiratory infections dropped from 159.8 to 95.3 per 1,000 people.

There’s also been a 35 percent increase in cycling in the city, likely due to the new bike paths built for the project. And biodiversity studies show wildlife is coming back; one sample of five Green Corridors identified 30 different species of butterfly.

Other cities are already taking note. Bogotá and Barranquilla have adopted similar plans, and last year São Paulo in Brazil — South America’s largest city — began expanding its corridors after launching them in 2022.

“For sure, Green Corridors could work in many other places,” says Zapata. But there are a few challenges. The corridors in the inner city have to contend with considerable pollution as traffic piles up. Often drivers will also dump trash along the corridors. And the city’s homeless are forced to take shelter in the spaces. 

“Like anything, nature requires maintenance from time to time,” adds Zapata. “You need to allocate a part of the budget for this.” The previous administration “didn’t give enough money” to maintain the corridors properly, she says, meaning some parts have become overgrown and dirty. 

That’s a particularly tricky issue as the city now finds itself US$2.8 billion in debt. Maintaining the city’s green corridors costs $625,000 a year, according to City Hall. 

But now that he’s back in office, Mayor Gutiérrez has pledged to reinvigorate the project of urban planting. And experimenting with new technology, such as “geotextile” pavements that can soak up rain and bend to allow tree roots to spread, is already underway.

“The plan is to plant more Green Corridors and link them to even more hills and streams, recovering what we have already planted,” says Gutiérrez. “It will be a more green Medellín.”

TOP A vertical garden at Medellin’s City Hall

ABOVE TOP A map of Medellín’s Green Corridors


PHOTOS Peter Yeung

The plan is to plant more Green Corridors and link them to even more hills and streams, recovering what we have already planted. It will be a more green Medellín.

Federico Gutiérrez


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