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.Given the current warming trend due to climate change and the global built environment expansion, the intensification of urban heat islands (UHI) is expected, accompanied by adverse impacts on population health.Urban green infrastructure can reduce local temperatures.We aimed to estimate the mortality burden that could be attributed to the UHI and the mortality burden that would be prevented by increasing the urban tree cover (TC) in 93 European cities. METHODS:We conducted a quantitative health impact assessment (HIA) for the summer (June-August) of 2015 to estimate the impact of the UHI, on all-cause mortality for adult residents (≥ 20 years old) in 93 European cities.In addition, we estimated the temperature reduction resulting by increasing the TC to 30% for each city and estimated the number of deaths that could be potentially prevented as a result with the aim of providing decisionmakers with usable evidence to promote greener cities.We performed all analyses at a highresolution grid-cell level (250m x 250m). FINDINGS:The population-weighted-city-average UHI from June to August was 1.5°C (city range 0.5°C -3.0°C).Overall,6,700 (95% CI 5,162) premature deaths could be attributable to the UHI (ie, 4.3%, city range 0.0%-14.8% of summer mortality, 1.8%, city range 0.0%-2.8% of annual mortality).Increasing the TC up to 30% at 250m resolution resulted in an average city cooling of 0.4ºC (city range 0.0ºC-1.3ºC).We estimated that 2,644 (95% CI 2,445-2,824) premature deaths (ie, 1.8%, city range 0.0%-10.8% of summer mortality, 0.4%, city range 0.0%-2.0% of annual mortality) could be prevented by increasing the average TC in cities to 30%. INTERPRETATION:Our results showed the impacts on mortality of the UHI and highlight the health benefits of green infrastructure to cool urban environments, while promoting more sustainable and climate-resilient cities.