The temperature difference that exists in the summer between an urban area (with less vegetation, more population and heating of the asphalt) and the surrounding areas is a phenomenon called the urban heat island and it is attributed to 4% of summer mortality in European cities. A third of these heat deaths could be prevented by increasing trees in cities by 30%.
Trees in the Casa de Camp de Madrid with the Plaza de España in the background. EFE/Juan Carlos Hidalgo
This is the main conclusion of a study on the urban heat island carried out in 93 European cities, including the Spanish cities of Madrid, Barcelona, Valencia, Malaga, Palma de Mallorca, Bilbao and Alicante, led by the ‘Global Health Institute of Barcelona (ISGLobal) and published in the scientific journal “The Lancet”.
The study’s findings underscore the salient benefits of planting more trees in cities to mitigate the impact of climate change.
Trees and their effect against heat in cities
From June to August 2015, cities were on average 1.5 degrees warmer than surrounding areas.
According to the study, 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 third of these deaths (2,644) could have been avoided by increasing tree cover to 30% of urban space, thus reducing temperatures.
In general, the cities with the highest rates of excess heat mortality were located in southern and eastern Europe, and these are the cities that would benefit most from an increase in tree cover.
The study highlights the substantial benefits of planting more trees in cities, although the authors acknowledge that this may be difficult in some cities due to their design, and that planting trees should be combined with other interventions such as green roofs or other alternatives to reduce the temperature.
The threat of climate change
Heat exposure has been associated with premature mortality, cardiorespiratory diseases and hospital admissions and not only with heat waves, but also with moderately high temperatures in summer, according to ISGlobal.
Cities are particularly vulnerable to high temperatures due to less vegetation, higher population density and impermeable building and street surfaces, including asphalt, which cause a temperature difference between the city and surrounding areas , the phenomenon known as the urban heat island.
“In view of global warming and urban growth, this effect is expected to worsen in the coming decades”, points out this research institute promoted by the La Caixa Foundation.
“Predictions based on current emissions reveal that heat-related illness and death will become a greater burden on our health services in the coming decades,” he says. Tamara Iungman, researcher at ISGlobal and first author of the study.
An international team led by Mark Nieuwenhuijsen, Director of ISGlobal’s Urban Planning, Environment and Health Initiativeestimated the death rates of people over 20 years of age living in 93 European cities (a total of 57 million inhabitants), between June and August 2015, and collected data on daily rural and urban temperatures for each city
First, they estimated premature mortality by simulating a hypothetical scenario without an urban heat island.
Second, they estimated the reduction in temperatures that would be obtained by increasing tree cover up to 30%, as well as the deaths that could be avoided.
“Our goal is to inform those responsible for local administrations of the advantages of integrating green areas in all neighborhoods to promote more sustainable, resilient and healthy urban environments,” explains Nieuwenhuijsen, in addition to preserving existing trees.
The analyzes were done with data from 2015 because population data for later years was not available, but as Tamara 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 problems and improvements to people’s cognitive function”, he adds.