Planting more trees in the city could reduce heat-related deaths by a third

More than 4% of deaths that occur in cities during the summer months are due to high temperatures. A 30% tree cover could reduce a third of these deaths, according to a modeling study published in The Lancet and led by the Barcelona Institute of Global Health (ISGlobal). The results, obtained with data from 93 European cities, emphasize the substantial benefits of planting more trees in cities to mitigate the impact of global warming.

Slightly higher summer temperatures can bring the same dangers as heat waves

Hot flashes are involved in premature mortality, cardiorespiratory diseases and hospital admissions. However, the moderately high temperatures of the summer period can also help with these problems. Cities are the most vulnerable places to this reality. Less vegetation, higher population density, and impermeable surfaces of buildings and streets cause a difference in temperature between the city and the surrounding areas. This phenomenon is known as the urban heat island and, given the climate crisis, it could get worse in the coming decades.

Infographic about heat islands. /ISGlobal

ISGlobal researcher and first author of the article, Tamara Iungman, told SINC that “all cities tend to be heat islands, but within the same city there is a lot of variability. For example, when we say that parks are the lungs of the city, we also mean that they provide cooling.”

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It’s important to start thinking about cities more in terms of people and less in terms of cars.

Tamara Ungman

The study highlights the substantial benefits of planting more trees in urban space. However, the authors recognize that the design of some cities can make it difficult to plant trees, so it should be combined with other alternatives, such as green roofs to reduce temperatures. For the most compact and dense urban areas, Iungman proposes “reducing the target to 25% and accompanying it with other strategies like vertical gardens, green roofs and replacing impermeable surfaces like asphalt with green surfaces.”

Benefits of including green infrastructure in urban areas.  /ISGlobal

Benefits of including green infrastructure in urban areas. /ISGlobal

This shift to comprehensive urban plans can bring huge benefits, “including improvements in mental and physical health, in addition to the environmental benefits themselves”, says the scientist. On the contrary, maintaining the current models can lead to serious health problems for residents of these areas.

Models inspired by the garden city refresh spaces in summer and benefit mental and physical health

“Forecasts based on current emissions reveal that heat-related illnesses and deaths will become a major burden on our health services in the coming decades,” said Iungman. “Our aim is to inform those responsible for local administrations about the advantages of integrating green areas in all neighborhoods to promote more sustainable, resilient and healthy urban environments”, adds Mark Nieuwenhuijsen, director of the Urban Planning Initiative, Environment Environment and Health from ISGlobal .

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Nieuwenhuijsen led a team that estimated death rates for residents aged 20 and over in 93 European cities – a total of 57 million people – between June and August 2015. The researchers also collected data on rural and urban daily temperatures for each City. First, they simulated a hypothetical scenario without an urban heat island to calculate premature mortality. Second, they estimated the temperature reduction that would be achieved by increasing tree cover by 30%, as well as the deaths that could be avoided.

The protective effect of trees

Cities were on average 1.5 degrees warmer than their surroundings during the summer of 2015. Around 6,700 premature deaths can be attributed to rising urban temperatures, accounting for 4.3% of total mortality during the summer months and 1 .8% of mortality throughout the year. A 30% increase in tree cover would have reduced temperatures, preventing a third of these deaths, totaling 2,644 deaths.

The areas where the most people live are those with the lowest percentage of trees showing

Tamara Ungman

“Our results also show the need to preserve and maintain the trees we already have because they are a valuable resource and new trees take a long time to grow. Also, it’s not just about the number of trees, but also how they are distributed. ” says Nieuwenhuijsen. In this regard, Iungman points out that “the areas where the most people live are those with the lowest percentage of trees, which indicates that the population is not benefiting from them and the impacts will be greater”.

The study gives some keys to make cities more resilient in the face of climate impact

The analyzes were done with data from 2015 because there was no population data for later years, but, as Iungman points out, the results are generalizable and the study provides valuable information to adapt our cities and make them more resilient to the impact of climate change. .

“Here we only look at the effect of trees on temperature, but increasing green areas in cities has many other health benefits, including increased life expectancy, reduced mental health issues and improvements in people’s cognitive function,” he adds. the scientist.

For Antonio Gasparrini, professor of Biostatistics and Epidemiology at the London School of Hygiene & Tropical Medicine, co-author of the study: “The vulnerability to heat changes from one city to another depending on several factors. trees can help inform measures to reduce risks and prevent preventable deaths, especially with climate change.”


Iungman, T. et al. Cooling cities for health through urban green infrastructure: a health impact assessment for European cities. The Lancet (2023).

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