For a cost of just $6.50 per person, the Colombian city of Medellín has cut its average temperature by 2°C.

It has done this using “green corridors” – lines of trees and plants that cost a total of $16.3 million to put in place and $625,000 a year to maintain.

And Medellín is not alone – other cities around the world are turning to natural solutions to reduce temperatures, which have been driven higher by the climate crisis and a phenomenon called the urban heat island effect, where city areas heat up more than rural ones due to building and road materials retaining heat.

Plants and trees help reduce heat levels by introducing water vapour into the environment. Image: World Economic Forum

Medellin’s “Green Corridors”

Medellín has a relatively constant temperature all year round of about 22-24°C, aided by its position in a valley surrounded by mountains. But, like many built-up areas across the globe, Colombia’s second-largest city has been warmer than surrounding rural areas.

A reduction in green areas and an increase in buildings and roads was partly to blame. A number of other issues including increased air pollution also played a part.

Solving the issue in a sustainable way was a key consideration for urban planners.

Green corridors – areas that are landscaped to promote more biodiversity – provide natural shade for urban areas. They also reduce heat levels through a process called evapotranspiration, which introduces water vapour into the environment.

The green corridor initiative in Medellín not only helped reduce temperatures by 2°C but also cut air pollution. These combined effects are making nature-based solutions increasingly popular among urban planners.

Strategic design in Singapore’s and Düsseldorf

Singapore has a land shortage and high population density, but despite its limited space it has developed a system of roads called Nature Ways that are lined with a diverse range of trees and shrubs, mimicking the structure of rainforests.

As well as reducing temperatures, the tree canopies protect animal species and cut air pollution. Singapore is now the second-highest ranked city on Treepedia’s Green View Index, which measures tree canopy cover in urban areas.

Over in Germany, Düsseldorf is home to a building covered with 30,000 plants that is helping to improve the city’s environment. Kö-Bogen II has hedges across its surface that were selected because of their ability to alter heat levels in the surrounding area.

The growth of “Nature-Positive Cities”

The World Economic Forum recently launched the Nature-Positive Cities initiative, which aims to help urban areas and businesses unite around common principles to build their relationship with nature.

The Forum is partnering with five “champion cities” to provide guidance on the implementation and delivery of nature-based interventions.

Barranquilla in Colombia is one of these cities. Its government recently published a long-term urban development plan called Barranquilla 2100 that outlines plans for nature restoration and biodiversity-centric urban revitalization.

Another of the champion cities is Incheon in South Korea, which has a target of cutting heatwave casualties to zero. It aims to achieve this with a four-pillar strategy that includes the installation of natural shading.

Rising heat risks for urban populations

Summer 2023 was the hottest on record, and even higher temperatures are expected in future. Of the world’s 576 largest urban areas, more than 70% – home to 1.4 billion people – are deemed to be at high or extreme risk from issues including extreme heat, according to the World Economic Forum’s BiodiverCities by 2030 report.

Cities are where 80% of global GDP comes from today, so future-proofing these areas is a vital part of our long-term ability to thrive, says the report.

The report calls on cities around the world to see the opportunities to embrace nature and live in balance with it, or face further natural ecosystem collapse. By measuring and highlighting the value of nature, urban planning can reflect the true value of nature-based urban solutions, it says.

Multiple stakeholders must work together to help cities tackle extreme heat. Image: World Economic Forum

“Nature-based solutions for urban infrastructure can provide 28% greater value than grey infrastructure alternatives in terms of positive environmental externalities and more resilient jobs, while costing 50% less, using today’s measures of economic cost,” it adds.