More greenery in urban areas could reduce all-cause mortality, study shows

A new analysis of greenery and mortality found that between 34,000-38,000 deaths could have been reduced with local increases in green vegetation in U.S. metropolitan areas.

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

Published in the magazine Limits in public health, the nationwide study found that increasing green vegetation in large, metropolitan areas could have prevented between 34,000-38,000 deaths, based on data from 2000-2019. The survey also found that overall greenness in urban areas has increased over the past 20 years, by nearly 3 percent between 2000-2010 and 11 percent between 2010-2019.

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

We know that living in greener areas can have a positive effect on our physical and mental health, but there is a lack of data on how changes in green distribution can affect death rates across the country. Our study quantifies the impact of the expansion of greenery in urban areas and shows how increasing green vegetation can potentially contribute to a person’s life expectancy. Policymakers and urban planners can use this information to support local climate action plans and ensure those plans include greening initiatives.”

Paige Brochu, lead author of the study, PhD student in the Department of Environmental Health

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

They estimate that overall greenness increased by 2.86 percent between 2000-2010 and 11.11 percent from 2010-2019, with the largest regional increase in the south (from 0.40 percent in 2000 to 0.47 percent in 2019).

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

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

“One of the key questions city planners are asking is where to implement greening, and can we quantify the impact of greening initiatives on them – because there are costs for tree-planting or shrub-planting campaigns,” said lead author Dr. Kevin Lane, assistant professor of environmental health. “Being able to target which areas would have the highest mortality reduction could justify these campaigns not only as a mitigation measure, but also as a way to directly improve health.”

Part of this assessment also formed the basis for a case study on the health effects of unequal landscaping 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 55 and older in the Louisville metro area.

The researchers hope to further investigate the 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 globally, thanks to the satellite-based NDVI measurements, Lane says.

“One of the great benefits of using satellite-based measurements is that we can compare US mortality and health impact assessments with those in Europe and other areas so that we can understand the global consequences of mortality,” Lane said. “This work will allow us to quantify whether a potential climate change adaptation strategy could impact not just 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 T.H. Chan School of Public Health.