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Doubling trees in European cities could prevent thousands of deaths

Doubling tree cover in European cities could cut the number of heat-related deaths during summer months by nearly 40 per cent, according to a modelling study.

The average canopy tree coverage in European cities is just under 15 per cent. This is defined as the area covered when viewed from above. Cities such as London and Barcelona are aiming to double this coverage to 30 per cent by 2030 and 2037, respectively.

To investigate the effect of achieving this, Tamara Iungman and her colleagues at the Barcelona Institute for Global Health, Spain, combined mortality data from 93 cities between June and August 2015 with daily temperature statistics to estimate the number of heat-related deaths over this three-month period.

The researchers have said they chose to study 2015 data because that is the most recent year for which European-wide statistics are available and its temperatures were typical of the current European climate.

They then modelled the impact on temperatures and mortality if tree cover in the cities increased.

“We already know that trees provide cooling,” says Mark Nieuwenhuijsen, a co-author of the study. The team set out to discover how much cooling trees provide and how many deaths they can prevent, he says.

Read more:

Trees cool the land surface temperature of cities by up to 12°C

Between June and August 2015, 6700 premature deaths occurred across the 93 cities due to extreme heat. Yet 2644 of these – nearly 40 per cent – could have been prevented by increasing tree cover to 30 per cent, the results suggest.

Trees help tackle a phenomenon known as the “urban heat island effect”, which sees temperatures in cities climb higher than in nearby rural areas. This is because urban surfaces, such as asphalt and concrete, absorb and retain heat. In some areas, the temperature difference between cities and nearby rural areas can be more than 4°C.

As climate change accelerates, cities must brace for increasingly extreme heatwaves, says Nieuwenhuijsen. In 2022, parts of the UK hit 40°C for the first time.

“Our city centres are too hot,” says Nieuwenhuijsen. “We can use nature-based solutions like tree planting to reduce the effect of the heat island and related mortality.”

The Lancet DOI: 10.1016/S0140-6736(22)02585-5

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