Trend Watch March 2024

How a Colombian city cooled dramatically in three years

Focusing on plants and people, Peter Yeung writes about how Medellín, known as the City of Eternal Spring with its year-round high temperatures, has created a people-led scheme of ‘green corridors’ to keep cool on the website ‘Reasons to be Cheerful.’

The project to plant and maintain hundreds of thousands of trees and plants across the city is carried out by 150 citizen-gardeners, who come from disadvantaged and minority backgrounds, with the support of 15 specialised forest engineers.

Yeung said: “The $16.3 million initiative led to the creation of 30 Green Corridors along the city’s roads and waterways, improving or producing more than 70 hectares of green space, which includes 20 kilometres of shaded routes with cycle lanes and pedestrian paths.

“The corridors are also designed to mimic a natural forest with levels of low, medium and high plants, including native and tropical plants, bamboo grasses and palm trees.

“Heat-trapping infrastructure like metro stations and bridges has also been greened as part of the project and government buildings have been adorned with green roofs and vertical gardens to beat the heat. 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.”

This project began with 120,000 individual plants and 12,500 trees and by 2021 had reached 2.5 million plants and 880,000 trees. Yeung says it could result in the city becoming “five degrees cooler over the next few decades.”

Though Yeung writes of the challenges too: “The corridors in the inner city areas have to contend with huge amounts of 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.”

Image: Mayor’s Office of Medellín.

Los Angeles just proved how spongy a city can be

Using sewers, gutters and infrastructure to channel rainwater out of cities quickly and avoid urban flooding is no longer working, writes Matt Simon of Wired. Instead making a city ‘spongy’ creates a ‘new bounce’.

Simon says: “The trick to making a city more absorbent is to add more gardens and other green spaces that allow water to percolate into underlying aquifers — porous subterranean materials that can hold water — which a city can then draw from in times of need. Engineers are also greening up medians and roadside areas to soak up the water that’d normally rush off streets, into sewers, and eventually out to sea.”

Rather than seeing 9 inches of rain over three days in Los Angeles as problematic, the city has taken measures to prepare. This includes replacing urban surfaces like concrete with natural surfaces, like dirt and plants, to create a ‘spongy’ city. Simon writes, “It has also built out ‘spreading grounds,’ where water accumulates and soaks into the earth.”

Manager of watershed management for the Los Angeles Department of Water and Power, Art Castro, says: “There’s going to be a lot more rain and a lot less snow, which is going to alter the way we capture snowmelt and the aqueduct water. Dams and spreading grounds are the workhorses of local stormwater capture for either flood protection or water supply.”

More urban spaces are starting to get ‘spongy’ too. Read more on Wired.

Photo: Nathan Dumlao on Unsplash.