Increasing greenery in urban areas can reduce all-cause mortality, study finds

New analysis on greenness and mortality found that between 34,000 and 38,000 deaths could have been reduced with local increases in green vegetation in US metropolitan areas.

According to a new study by researchers at the Boston University School of Public Health, increasing greenery in US urban areas could significantly reduce all-cause mortality.

Published in the journal Frontiers in public healththe national study found that increasing green vegetation in major metropolitan areas could have prevented between 34,000 and 38,000 deaths, based on data from 2000 to 2019. The study also showed that greenery overall in metropolitan areas has increased over the past 20 years, by almost 3% between 2000 and 2010 and by 11% between 2010 and 2019.

The study builds on well-established research on the health benefits of greening by providing a quantitative value to the potential impact of urban greening initiatives on mortality.

“We know that living in greener areas can have a positive impact on our physical and mental health, but there is a lack of data on how changes in the distribution of greenery can affect death rates across country,” said the study’s lead author, Paige Brochu. , PhD student in the Department of Environmental Health. “Our study quantifies the impact of expanding greenery in urban areas and shows how increasing green vegetation could potentially increase a person’s life expectancy. Policy makers and urban planners can use these information to support local climate action plans and ensure those plans include greening initiatives.”

For the study, Brochu and his colleagues used publicly available population data from the U.S. Census, mortality data from the Centers for Disease Control’s WONDER system, and greenery data from NASA’s Landsat satellites to conduct an assessment of national scale health impact which estimated the increased impact of green vegetation on all causes. mortality among adults age 65 and older in 35 major US metropolitan areas. The study period focused on three distinct periods over a 20-year period: 2000, 2010, and 2019. Using the Normalized Difference Vegetation Index (NDVI), a widely used measure that estimates the amount of green vegetation, the researchers calculated that 34,080 -38,187 elderly deaths – or about 15-20 deaths per 10,000 elderly people – could have been avoided between 2000 and 2019 with a 0.1 increase in NDVI in the 35 metropolitan areas.

They estimated that overall greenness increased by 2.86% between 2000 and 2010 and by 11.11% between 2010 and 2019, with the largest regional increase observed in the South (from 0.40% in 2000 to 0. 47% in 2019).

Brochu notes that greening may not be feasible in all cities, due to differences in climate, water sources, urbanization, and landscape, but city planners can use the study results to examine local changes in greenness over time and develop appropriate and effective climate action. plan in their cities.

“Increasing greenery in an arid Southwest climate is different from increasing greenery in an urban area of ​​the Pacific Northwest,” says Brochu. “If a region’s climate makes it difficult to plant lush trees, city planners can use this greenery data as a starting point and consider other types of vegetation that may be more realistic for their local climate.”

“One of the main questions for city planners is where should they implement greening, and can we quantify the impact of greening initiatives for them; as there is a cost to greening campaigns planting trees or planting shrubs,” says the study’s lead author, Dr. Kevin Lane, assistant professor of environmental health. “Being able to target areas that would have the greatest reduction in mortality can justify these campaigns, not just as a mitigation measure, but as a way to directly improve health.”

An element of this assessment also informed a case study on the health impacts of inequitable distribution of greenery in Louisville, Kentucky, which was published in the 2020 report of The Lancet Countdown on climate and health. The case study estimated that a small increase in greening could have prevented 400 deaths among adults age 55 and older in the Louisville metro area.

The researchers hope to further explore local changes in the distribution of greenery in other urban areas, and how these changes may have informed cities’ climate action plans. This analysis could also be replicated on a global scale, thanks to satellite-based NDVI measurements, Lane says.

“One of the big advantages of using satellite measurements is that we can compare US assessments of the health impact of mortality to those done in Europe and other regions, so we can understand the global mortality impacts,” Lane said. “This work will allow us to quantify whether a potential climate change adaptation strategy could have impacts not just in our urban areas, but around the world.”

At SPH, the study was co-authored by Dr. Patrick Kinney, Beverly A. Brown Professor of Urban Health and Dr. Marcia Pescador Jimenez, assistant professor of epidemiology. The study was also co-authored by Dr. Peter James of Harvard Pilgrim Health Care and Harvard TH Chan School of Public Health.

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