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Increasing urban vegetation by 30% could have saved more than one-third of all heat-related deaths, saving up to 1.16 million lives globally from 2000 to 2019 according to a 20-year modeling study of the impact of increasing greenness in more than 11,000 urban areas.

The study, led by Monash University Professor Yuming Guo and in The Lancet Planetary Health, showed that increasing vegetation levels by 10%, 20% and 30% would decrease the global population-weighted warm-season mean temperature by 0.08°C, 0.14°C, and 0.19°C, respectively. It could prevent 0.86, 1.02, and 1.16 million deaths, respectively, representing 27.16%, 32.22%, and 36.66% of all heat-related deaths from 2000 to 2019.

The effect of increased urban vegetation on health is affected by different climate types, greenness levels, socioeconomic statuses and demographic characteristics. Urban areas in Southern Asia, Eastern Europe, and Eastern Asia have seen the greatest reduction in heat-related deaths.

The study aimed to detect the potential reduction in global heat-related deaths by increasing greenness in the warm season from 2000 to 2019 in 11,534 urban areas. Heat-mortality associations were assessed by using data from 830 locations in 53 countries and extrapolated to each urban center.

While increasing greenness has been proposed as a heat-related death mitigation strategy, according to Professor Guo, this is the first modeling study to estimate both the cooling and modifying effects of greenness.

"This gives us a more comprehensive assessment of its benefits in mitigating heat-related mortality," Professor Guo said.

"These findings indicate that preserving and expanding greenness might be potential strategies to lower temperature and mitigate the health impacts of heat exposure."

Heat exposure is a major public health threat and is increasing due to climate change. Between 2000 and 2019, heat exposure was associated with 0.5 million deaths per year, accounting for 0.91% of global mortality. According to Professor Guo, estimates of heat-related deaths are projected to range from 2.5% in North Europe to 16.7% in South-East Asia during 2090–99, "under the most extreme global warming scenarios."

Studies show that greenness has a cooling effect on temperature, via shading surfaces, deflecting radiation from the sun, and evapotranspiration (evaporation from both the ground and plants) which promotes air convection. This, in turn, cools the ambient temperature, leading to a decrease in population heat exposure, thereby reducing the heat-related mortality burden.

According to Professor Guo, emerging evidence has also shown that greenness could modify the heat-related mortality risk, potentially related to factors such as mental health, social engagement, physical activity and air pollution.

The researchers used data from the Multi-Country Multi-City (MCC) Collaborative Research Network, which was developed in 2014 to look at population-wide associations between environmental stressors, climate and health across countries and regions. In this study, daily mortality and weather variables were extracted from 830 locations in 53 countries.

Greenness was measured via the Enhanced Vegetation Index (EVI), a satellite-based vegetation index derived from images collected by the National Aeronautics and Space Administration's Terra satellite. An "urban area" was defined as an area with a density of at least 1,500 inhabitants per km² of permanent land and a total population of more than 50,000.

If the level of vegetation is increased by 30% the average number of lives saved from 2000 to 2019 by region is:

• ·¡³Ü°ù´Ç±è±ð—396,955
• North America—69,306
• Latin American and the Caribbean—123,085
• ´¡´Ú°ù¾±³¦²¹â€”35,853
• ´¡²õ¾±²¹â€”527,989
• °¿³¦±ð²¹²Ô¾±²¹â€”2,733
• Australia and New Zealand—2,759