Inequality related to urban greenness is increasing, study shows

December 20, 2017

Not only is urban greenness unequally distributed by neighborhood demographics, but poorer neighborhoods and those with more minorities are losing greenness, according to a recent UC Berkeley led study. The study, published on December 10 in the International Journal of Environmental Research and Public Health, examined urban greenness in almost 60,000 urban census tracts in the United States between 2001 and 2011.

Previous research has shown that greenness in urban areas is not evenly distributed, and that areas with higher socioeconomic status often have more greenspace and parks. This is the first known study to look at neighborhood greenness across the entire United States over time to assess whether the inequality is improving or getting worse.

“Parks and other green spaces in cities confer many public health benefits to community members,” said Rachel Morello-Frosch, senior author of the study and professor with the UC Berkeley School of Public Health and Department of Environmental Science, Policy, and Management. “This study shows that these benefits are unequally distributed in the United States, and these disparities are not improving.”

Researchers used the normalized difference vegetation index (NDVI), a measure of vegetation based on remote sensing data and the light absorption characteristics of chlorophyll, to establish a baseline of greenness in 2001 and evaluate the changes over time. Higher neighborhood NDVI has been previously linked with reductions in mortality and increased birth weight.

The researchers included five racial/ethnic groups in the study: non-Hispanic Asians and Pacific Islanders; non-Hispanic American Indians; non-Hispanic Blacks, Hispanics of any race; and non-Hispanic Whites. The models adjusted for population density, climatic factors, housing tenure, and Index of Concentration at the Extremes for income (ICE)—a measure of neighborhood-level concentration of poverty and affluence.

The analysis showed that on average, census tracts became less green by 2011, particularly in the southern United States. But NDVI on average went up in census tracts with a higher proportion of White individuals. For communities with a higher percentage of Asian, Black, and Hispanic individuals, there was a negative correlation with NDVI over time. Census tracts composed of relatively more Hispanic residents had the largest decreases in greenness over time and affluent tracts (estimated by ICE) composed of more non-Hispanic White residents had the largest increases in greenness over the study period.

The research did not identify the fundamental drivers of these disparities. Also, NDVI imagery does not capture the differences in quality of vegetation, i.e. the difference between a well-maintained park and a vacant lot overgrown with weeds. Future research should look at potential disparities in the built environment and land use patterns of the green spaces, suggest the study authors.

“City planners and public health practitioners can do a better job of incentivizing greenspace development to promote healthier neighborhoods in disadvantaged communities,” said Joan Casey, a postdoctoral scholar in the School of Public Health and the Department of Environmental Science, Policy and Management, and lead author on the study.

By Linda Anderberg