How cities around the world are finding ways to beat extreme heat

BOGOTA - With heatwaves breaking records around the world, urban planners and local officials are coming up with solutions to keep sweltering cities cooler, and save lives.

By 2050, heatwaves will affect more than 3.5 billion people globally – half of them in urban centres - according to the U.S.-based Adrienne Arsht-Rockefeller Foundation Resilience Center (Arsht-Rock).  

Cities are often several degrees warmer than nearby rural areas because heat trapped by concrete and dark-coloured roads and buildings creates a "heat island" effect, meaning night-time temperatures also remain high.

It is often people living in poor neighbourhoods that tend to suffer the potentially lethal effects of extreme heat because of a lack of trees, shade and parks.

Unless planet-heating greenhouse gas emissions are slashed by 2050, 1,000 cities will experience average summer highs of 35 degrees Celsius (95 Fahrenheit), nearly triple the current number, according to U.N. estimates.

Here's how global cities are responding:

Going green

A 2023 modelling study by a team of researchers based on 93 cities in Europe found increasing tree cover from the European city average of 14.9% to 30% can lower the urban temperature by 0.4 C (0.72 F), which could cut heat-related deaths by a third.

From Sydney and Shanghai to Vancouver and Johannesburg, numerous cities have stepped up efforts to make urban landscapes greener by planting trees and vegetation on the walls and roofs of buildings to provide shade and help reduce temperatures.

Green roofs absorb heat and act as insulators, reducing the energy needed to provide cooling and heating, according to the U.S. Environmental Protection Agency (EPA).

Singapore is one city leading the way by making 100 hectares (247 acres) of building facades greener - a figure the city aims to double by 2030 - and developing about 50 nature paths.

In Medellin, Colombia's second-largest city, an award-winning network of some 30 connected green corridors of trees and vegetation provide shady paths for pedestrians and cyclists.

And in Paris, the "Oasis schoolyard project" aims to tackle the heat island effect by transforming 770 public playgrounds into shadier spaces with more trees by 2040.

Wind power

Tall wind towers, known as wind catchers, have been used for centuries in parts of the Middle East, North Africa and Asia as a natural ventilation system to help cities keep cool.

The traditional chimney-like architectural feature found on the rooftops of buildings and houses has vertical slots to catch and channel the movement of air driven by wind.

Harnessing wind flows can reduce the heat island effect.

In Singapore, for example, urban planners and developers of new high-rise tower blocks aim to harness the wind by creating a network of wind corridors to maximise natural wind flows and minimise trapped heat during different monsoon periods.

Water relief

Large ponds, canals and rivers shaded by trees can help to lower temperatures in surrounding areas, while fountains, spray parks and misting stations can cool the air and provide immediate relief to passing pedestrians.

In South Korea's capital, Seoul, the city government worked with residents to restore the Cheonggyecheon Stream, a river once covered by a highway overpass for decades.

The nature revival project, carried out in the early 2000s, has stemmed flooding and lowered temperatures by reducing the heat island effect.

Research shows temperatures along the river that runs through downtown Seoul are 3.3 C-5.9 C (5.9 F-10.6 F) cooler than on a parallel road just blocks away.

Cool roofs

Painting roofs with a reflective white coat is a low-cost and simple way to reduce indoor temperatures by up to 5 C (9 F), according to the United Nations.

In the Indian city of Ahmedabad, in response to a devastating 2010 heatwave that killed more than 1,300 people, thousands of roofs have been painted white in slum areas - prompting dozens of other Indian cities to take similar action.

In New York City, the "Cool Roofs" programme that began in 2009 has led to more than 10 million square feet (929,000 square metres) of rooftops being painted white.

Similar initiatives have been implemented in Washington D.C., and in Toronto where the city's "Eco-Roof" programme provides financial incentives.

Reflective roads

Dark roads and concrete surfaces absorb and then radiate heat. This heat island effect means daytime temperatures in urban areas are about 0.6 C-3.9 C (1 F-7 F) higher than in surrounding areas, the U.S. EPA says.

U.S. cities from Los Angeles to Phoenix, along with Tokyo and other capitals around the world have covered roads, pavements, parking lots, and sports courts with solar-blocking light-coloured reflective paint.

In Phoenix, about 118 miles (189 km) of streets have been given the cool pavement treatment with special asphalt coatings.

Pavements with the coating can be up to 6.7 C (12F) cooler than roads covered with standard asphalt paint at noon and during the afternoon, Phoenix officials say.

Reviving ancient wisdom

Traditional building techniques that promote natural ventilation are being revived in Guangzhou, one of China's largest cities with a population of about 19 million people.

The city's historic Yongqing Fang neighborhood has incorporated cooling alleys, hollow walls, and double-layered tiled roofs that insulate against heat.

(Reporting by Anastasia Moloney in Bogota; Editing by Helen Popper.)