Urban Think Tank: growing green corridors to tackle urban heat

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Region: Colombia

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After enduring years of high crime and violence, the Colombian city of Medellín faces a new threat – rising urban temperatures, driven by climate change. The city’s response has brought people together, planting vegetation along busy streets and former waterways to lower temperatures and create a better environment for all residents. 

The initiative has improved health and biodiversity, and created job opportunities for marginalised people. Now, with a solid business case and record of success, the team behind the scheme are aiming to help other city authorities grown their own green corridors. 

Lower temperatures, new jobs and greener travel: the case for green corridors

Since 2016 Medellín’s green corridors have shaded cyclists and pedestrians, cooled built up areas and cleaned the air along busy roads. 880,000 trees and 2.5 million smaller plants have sprung up around the city. As part of the initiative, the city’s botanical gardens train people from disadvantaged backgrounds to become city gardeners and planting technicians. 

The scheme was initially a collaboration between La Universidad Pontificia Bolivariana Medellín and the city’s mayoral office (ACI Medellín). Secretary of Environment Sergio Orozco explained: “The programme came from the need to connect people to nature – recovering spaces that were occupied by concrete.” Now the work is set to be taken forward in other cities by consultancy Urban Think Tank Next. 

The programme has achieved huge heat reductions in Medellin. From 2016 to 2019 average air temperatures in the city’s Green Corridors locations fell from 31.6C to 27.1C. Pollutants such as PM2.5, PM10 and Ozone have fallen too. 

This brought huge health benefits. In the same period, the city’s morbidity rate from acute respiratory infections fell by more than 30%. Cycling journeys rose by 35%, and walking journeys rose by 4%. This surge in cycling was aided by the construction of 80km of new bike paths as part of the project. 

Finally, the scheme brought huge training and employment opportunities. 107 people from disadvantaged communities were trained as gardeners, and 2,600 workers were employed through the project. 

The overall cost of the work was around $180 million USD, or an average of 120 USD for each square metre transformed by the initiative. Every aspect of the scheme – from lower temperatures and better health to training opportunities – has created progress towards a fairer, more equal Medellín. 

The lungs of the city

Medellín’s Popular 2 neighbourhood was built on a steep hillside by people fleeing violence in the surrounding region. But the wooden homes in this cramped corner of the city were vulnerable to fire, and the river that runs through it became polluted with rubbish and dead animals. 

But helping local people create of a new park at heart of the community, under the green corridor scheme, has tackled these problems – and brought many more benefits. Community leader Maria Emilce Usuga. She says: “Now, you see more people out… at night, you see lots of couples, kids playing, kicking around a ball.”  

She adds that the new green space has boosted residents’ health. “To me, nature also has a lot to do with the health of a person, their emotional and physical well-being. How could clean air not be better than polluted air?” 

The green corridors are tended by community gardeners from disadvantaged backgrounds, recruited by the city authorities as part of a social inclusion programme. They include single mother Marta Girlesa Morena, who earns a living maintaining the corridors and the city’s botanical garden.  

“We are the lungs of the city,” she says. Marta plants, picks weeds, clears rubbish, and talks to people about the city’s vegetation and the importance of biodiversity. 

Bringing green corridors to Barranquilla

The team behind the initiative is now launching a trial green corridors project in the coastal Colombian city of Barranquilla, home to 2.2 million people. In two central public spaces – the River Administration Square and Square of the Church of San Nicolás de Tolentino – close to 100 trees will be planted, and natural floors will replace paving. 

This will lower average high temperatures at the two sites (currently 34 and 36 degrees Celsius) by up to 8 degrees. The introduction of natural floors will also help address urban flooding – a danger that kills 25 people in the city every year. 

The scheme will bring social and economic benefits to the city and its residents, helping people work and relax. In River Administration Square, local fishers will be able to sell their daily catch outdoors. In the church square – currently unused during the hottest parts of the day – cafes and other local businesses will make use of the cooler space. The planting and construction work is set to provide 175 jobs. 

Nourishing green corridors around the world

With support from Ashden’s Fair Cooling Fund, the team behind the green corridors have analysed and documented the approaches that made the scheme a success, and detailed the business case that will allow more cities to invest in this solution.  

Alejandro Restrepo Montoya was Director of the Office of Strategic Urban Projects of the Medellín Mayor’s Office between 2016 and 2019, and is now a member of Urban Think Tank Next. He said: “Worldwide, the number of cities exposed to extreme temperatures will nearly triple by 2050. Green corridors are a proven and cost-effective tool to reduce urban heat, boost health, support local economies and tackle inequality.  

“We want to bring these benefits to more cities around the world. We’re seeking new partners, in Latin America and beyond, who can help us reach this goal.” 

Contact Urban Think Tank for more information

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