Cooling cities through urban green infrastructure: a health impact assessment of European cities

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 mean that the intensification of urban heat islands (UHIs) is expected, accompanied by adverse effects on population health. Urban green infrastructure can reduce local temperatures. We aimed to estimate the mortality burden that could be attributed to UHIs and the mortality burden that would be prevented by increasing urban tree coverage in 93 European cities. Methods We did a quantitative health impact assessment for summer (June 1-Aug 31), 2015, of the effect of UHIs on all-cause mortality for adults aged 20 years or older in 93 European cities. We also estimated the temperature reductions that would result from increasing tree coverage to 30% for each city and estimated the number of deaths that could be potentially prevented as a result. We did all analyses at a high-resolution grid-cell level (250 x 250 m). We propagated uncertainties in input analyses by using Monte Carlo simulations to obtain point estimates and 95% CIs. We also did sensitivity analyses to test the robustness of our estimates. Findings The population-weighted mean city temperature increase due to UHI effects was 1 center dot 5 degrees C (SD 0 center dot 5; range 0 center dot 5-3 center dot 0). Overall, 6700 (95% CI 5254-8162) premature deaths could be attributable to the effects of UHIs (corresponding to around 4 center dot 33% [95% CI 3 center dot 37-5 center dot 28] of all summer deaths). We estimated that increasing tree coverage to 30% would cool cities by a mean of 0 center dot 4 degrees C (SD 0 center dot 2; range 0 center dot 0-1 center dot 3). We also estimated that 2644 (95% CI 2444-2824) premature deaths could be prevented by increasing city tree coverage to 30%, corresponding to 1 center dot 84% (1 center dot 69-1 center dot 97) of all summer deaths. Interpretation Our results showed the deleterious effects of UHIs on mortality and highlighted the health benefits of increasing tree coverage to cool urban environments, which would also result in more sustainable and climateresilient cities. Copyright (c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

This study shows that urban heat islands have a negative impact on mortality, but increasing tree coverage in cities can help reduce temperatures and prevent premature deaths.