Summary Background High ambient temperatures are associated with many health effects, including premature mortality. The combination of global warming due to climate change and the expansion of the global built environment means that the intensification of urban heat islands (UHIs) is expected, accompanied by adverse effects on population health. Urban green infrastructure can reduce local temperatures. Our objective was to estimate the mortality burden that could be attributed to UHIs and the mortality burden that would be avoided by increasing urban tree cover in 93 European cities. Methods We did a quantitative summer health impact assessment (June 1 to August 31, 2015) of the effect of UHIs on all-cause mortality for adults aged 20 years and older in 93 European cities. We also estimated the temperature reductions that would result from increasing tree cover to 30% for each city and estimated the number of deaths that could be prevented as a result. We did all analyzes at a high-resolution grid cell level (250 × 250 m). We propagate uncertainties in the input analyzes by using Monte Carlo simulations to obtain point estimates and 95% CIs. We also did sensitivity analyzes to test the robustness of our estimates. Results The population-weighted mean city temperature increase due to UHI effects was 1.5°C (SD 0.5; range 0.5 to 3.0). Overall, 6700 (95% CI 5254–8162) premature deaths could be attributed to the effects of UHI (corresponding to about 4·33% [95% CI 3·37–5·28] of all summer deaths). We estimate that increasing tree cover to 30% would cool cities by an average of 0.4°C (SD 0.2; range 0.0–1.3). We also estimate that 2644 (95% CI 2444–2824) premature deaths could be prevented by increasing the city’s tree cover to 30%, corresponding to 1.84% (1.69–1.97) of all premature deaths. summer. Interpretation Our results showed the harmful effects of UHIs on mortality and highlighted the health benefits of increasing tree cover to cool urban environments, which would also result in more sustainable and climate-resilient cities. Money GoGreenRoutes , Spanish Ministry of Science and Innovation, Institute for Global Health, UK Medical Research Council, European Union Horizon 2020 project exhaustion. |
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Planting more trees could reduce deaths from higher summer temperatures in cities by a third, modeling study suggests
- Modeling of 93 European cities finds that increasing tree cover by up to 30% can help reduce the temperature of urban environments by an average of 0.4 degrees and prevent heat-related deaths. (The average tree cover in European cities is currently 14.9%).
- Of the 6,700 premature deaths attributed to rising temperatures in cities during 2015, a third of these (2,644) could have been avoided by increasing urban trees by up to 30%.
- The authors note that these findings highlight the need to integrate more sustainable and climate-resilient strategies into local policy decisions to help adapt to climate change and improve population health.
A third of premature deaths attributable to rising temperatures in European cities during the summer of 2015 could have been avoided by increasing urban forest cover by up to 30%, a modeling study published in The Lancet reveals . The study also found that tree cover reduced urban temperatures by an average of 0.4 degrees during the summer.
“We already know that high temperatures in urban environments are associated with negative health outcomes, such as cardiorespiratory failure, hospital admission and premature death. “This study is the largest of its kind and the first to specifically look at premature mortality caused by higher temperatures in cities and the number of deaths that could be prevented by increasing tree cover,” says lead author Tamar Lungman, Institute of Barcelona for Global Development. Health.
“Our ultimate goal is to inform local policy and decision makers about the benefits of strategically integrating green infrastructure into urban planning to promote more sustainable, resilient and healthy urban environments and contribute to the adaptation and mitigation of change. climate. This becomes increasingly urgent as Europe experiences more extreme temperature fluctuations caused by climate change; Although cold conditions currently cause more deaths in Europe, predictions based on current emissions reveal that heat-related illnesses and deaths will place a greater burden on our health services over the next decade.”
Urban environments record higher temperatures than the surrounding countryside, generally known as "urban heat islands" . This temperature difference is caused by human modification of landscapes, such as the removal of vegetation, the presence of asphalt, and the use of building materials that absorb and trap heat. As emissions continue to exacerbate climate change and global warming, rising temperatures in cities are expected to become more intense, creating an increasingly urgent need for cities to adapt to improve outcomes. of health.
The researchers estimated mortality rates for residents over the age of 20 in 93 European cities (listed in the appendix) between June and August 2015, representing a total of 57 million inhabitants. Mortality data from this period were analyzed with the city’s daily average temperatures in two modeling scenarios: the first comparing the temperature of the city without urban heat islands with the temperature of the city with urban heat islands, and the second, simulating the reduction in temperature as a consequence of increasing tree cover to 30%. Exposure response functions were used to estimate the number of deaths attributable to urban heat, as well as the number of deaths that could be prevented by increasing tree cover.
The population-weighted average daily city temperature difference between cities and countryside from June to August 2015 was 1.5 degrees warmer than the surrounding countryside, with the maximum temperature difference measured at 4.1 degrees warmer hot in Cluj-Napoca, Romania. In all cities, 75% of the total population lived in areas with an average city summer temperature difference of more than one degree, and 20% with an average summer temperature difference of more than two degrees, in comparison with the surrounding field.
In total, 6,700 premature deaths could be attributed to higher urban temperatures during the summer months, representing 4.3% of summer mortality and 1.8% of year-round mortality. One in three of these deaths (2,644 in total) could have been prevented by increasing forest cover by up to 30% and therefore reducing temperatures. This corresponds to 39.5% of all deaths attributable to higher urban temperatures, 1.8% of all summer deaths and 0.4% of year-round deaths.
There was large variability in temperature-related mortality rates between cities, from no premature deaths attributable to higher urban temperatures in Goteborg, Sweden, to 32 premature deaths per 100,000 inhabitants in Cluj-Napoca, Romania. In general, the cities with the highest temperature death rates were in southern and eastern Europe, where the highest temperatures were reached, and these cities benefited most from an increase in tree cover.
The results of this study support the idea that urban trees provide important public health and environmental benefits; However, the authors recognize that increasing tree cover should be combined with other interventions to maximize urban temperature reduction (for example, changing ground surface materials to reduce nighttime temperatures, such as replacing asphalt with trees) . Achieving the 30% tree cover target may be a major challenge for some cities due to urban design, with the average tree cover of cities in Europe currently at 14.9%.
“Our results suggest large impacts on mortality due to higher temperatures in cities, and that these impacts could be partially reduced by increasing tree cover to help cool urban environments. We encourage urban planners and decision makers to incorporate urban green infrastructure tailored to each local environment while combining it with other interventions to maximize health benefits and promote more sustainable and resilient cities, especially as we already know that green spaces They may have additional health benefits. such as reducing cardiovascular disease, dementia and poor mental health, improving cognitive functioning in children and the elderly and improving the health of babies,” says study co-author Mark Nieuwenhuijsen, Director of Urban Planning, Environment and Health. from the Barcelona Institute for Global Health. [1]
The authors acknowledge some limitations of this study. The study could not be conducted for a year more recent than 2015, due to the lack of availability of population data. Additionally, a US data set was used to build the cooling model in the study instead of a European data set. Finally, this study focused on the health impacts of high temperatures, but did not look at cold temperature. While cold temperatures currently have a greater health impact in Europe, health impacts due to heat are projected to exceed those caused by cold under current emissions scenarios, highlighting the importance of adapting our cities now .
Writing in a linked comment, Kristie Ebi of the University of Washington, US, who was not involved in the research, said: “Essentially all heat wave-related deaths are preventable; no one needs to die from the heat. With climate change projected to increase the frequency, intensity and duration of extreme heat events, communities must understand the most effective interventions, particularly the development and implementation of heat wave early warning and response systems. Equally important are Heat Action Plans that explicitly incorporate the consequences of a changing climate into longer-term urban planning. Heat Action Plans detail how to modify urban form and infrastructure to increase the resilience and sustainability of our communities as we face an even warmer future. Encouraging and enabling decision makers and local communities to develop and implement the Heat Action Plan is an effective way to promote climate resilience as high temperatures continue to be felt globally. Tools and guidelines are available; The gaps are in human and financial resources for implementation. The time to start is now."
