Medellin, Colombia, has successfully reduced its average temperature by 2 degrees Celsius through the implementation of “green corridors”, or strategically planted lines of trees and vegetation.
This initiative, which cost US$16.3 million to establish and now costs US$625,000 annually for maintenance, addresses the urban heat island effect that had made the city warmer than its surrounding areas and increased the risk of forest fires.
Medellin’s tree planting initiative: A smart strategy to combat urban heat
Prior to introducing green corridors, Medellin had experienced years of rapid urban expansion, characterized by a reduction in green spaces and the expansion of buildings and roads across the city. This had resulted in an urban heat island effect, causing temperatures in the city to become significantly higher than the surrounding rural areas. This occurs because buildings, roads and other infrastructure absorb and re-emit the sun’s heat for longer than natural landscapes such as trees, forests, fields and water bodies.
In an attempt to address the city’s rising temperatures, as well as its pollution, Medellin’s then mayor, Federico Gutiérrez (who, after completing one term in 2019, was re-elected at the end of last year) decided to introduce the tree-planting initiative. 30 green corridors were planted along the city’s roads and waterways, connecting newly-greened road verges, streams, parks, vertical gardens, and hills.
This produced more than 70 hectares of green space, including 20 kilometers of tree-lined and shaded routes for cyclists and pedestrians. Initially, approximately 120,000 new plants and 12,500 trees were planted on roads and parks, before an additional 2.5 million smaller plants and 880,000 trees were planted across the city by 2021.
The green corridors had a clear impact in reversing the city’s heat island effect. Through a process called evapotranspiration, the newly-planted vegetation began to release water vapor into the atmosphere, reducing the temperature and helping improve air quality. Remarkably, temperatures fell by 2 degrees Celsius in the first three years of the program, and officials expect a further decrease of 4 to 5 degrees Celsius over the next few decades, even accounting for climate change.
A study by C40 Cities, an urbanism and climate change organization, showed that vegetation growth in just one of Medellin’s 30 green corridors would absorb 160,787 kg of CO2 per year, or 2,308,505 kg of CO2 over the next century – the equivalent of taking 500 cars off the road.
A model for climate-resilient cities of the future?
In addition to reducing heat and improving air quality, experts say that Medellin’s tree-planting program has also led to a 34.6 increase in cycling in the city, generating further benefits to the health of its residents. It has also brought wildlife back to the city. As the city continues to implement the initiative – urban planting continues to this day via a team of citizen-gardeners – it is truly embodying its reputation as “The City of Eternal Spring.”
While the Medellin’s green corridors project has garnered much support from the city’s residents, it has also become well-known around the world due to its impressive results in reducing temperatures. Other Colombian cities, including Bogota and Barranquilla have adopted similar plans. Sao Paulo – South America’s largest city – has also expanded its own version of the corridors. Cities such as Düsseldorf and Singapore are also planting trees and shrubs along their roads to tackle heat and enhance urban living.
As summer 2023 was the hottest ever recorded, and with even higher temperatures expected in the future, the need to address heat problems in cities is more urgent than ever. The World Economic Forum’s BiodiverCities by 2030 report reveals that over 70 percent of the world’s 576 largest urban areas, which cumulatively are home to 1.4 billion people, are at high or extreme risk from issues relating to extreme heat.
The report emphasizes that nature-based solutions for urban infrastructure can provide 2 percent more value than traditional gray infrastructure, offering significant environmental benefits while costing 50 percent less. This reiterates the value of initiatives such as tree-planting and green corridors.
In Colombia, drought and a resultant spate of forest fires have recently brought the effects of climate change into particularly strong focus. While the National Unit for Disaster Risk Management (UNGRD) recently announced that there are currently no active forest fires in the country, a report from the country’s National Crisis Room indicated that in September 2024 there were 491 forest fires affecting 236 municipalities.
Finding innovative solutions to these challenges is crucial for communities facing the impacts of global warming. In Colombia and elsewhere, initiatives like green corridors are essential for building environmental resilience and creating a sustainable future for urban populations.