“The best time to plant a tree was 20 years ago. The second-best time is now.”
Trees evolved over hundreds of millions of years to retain water, absorb pollution, provide shade, and prevent erosion, making them excellent at reducing climate change in cities. Yet not all urban tree canopies are created equal. Many cities around the country have tree-planting programs, however, the programs and distribution of trees can be spotty, leaving some neighborhoods without trees to absorb the heat refracting off streets, sidewalks, and buildings. Understanding who’s protected by trees and who isn’t provides insights into human wellbeing and stressors.
On November 14, Greenlink Analytics launched a new novel dataset "Urban Tree Canopy,” a tool that allows users to see the distribution of trees across city neighborhoods. The tool is part of the Greenlink Equity Map, which already measures urban heat islands among more than 30 other environmental and social disparities. The tool’s sophisticated interface not only helps reveal tree cover, but also the relationship between tree cover and other inequities.
“People are suffering unnecessarily,” says Sharanya Madhavan, data scientist and team lead and creator of Greenlink’s Urban Tree Canopy tool. “Understanding the intersections between trees, heat, health, and energy are really important.”
[City of Atlanta skyline and the Urban Tree Canopy map]
The Greenlink team undertook a detailed analysis combined with machine learning techniques to evaluate the percent of urban tree canopy across all metro areas in the United States. The data relied on satellite imagery from the summer season on cloudless days. All images were captured at 10am with a single map pixel representing a 30-meter squared swath of land. In this way the team provided a high-resolution, detailed analysis of 378 metro areas with a greater than 90 percent accuracy..
The aim was to provide a tree canopy score – based on percentage - across area codes to reveal the inequitable distribution of risks across different populations within the same urban area. For example, in Baltimore, Md., one neighborhood has an energy burden of 22 percent and zero percent tree canopy cover, while another has a one percent energy burden and 54 percent tree cover. This way people could start answering questions like, where are the neighborhoods with fewer trees and what’s the relationship between lack of tree coverage and also suffering from high heat intensity, high energy bills, and high asthma rates. The GEM tool allows users to see these stats in visual and granular detail.
“A lot of city planners are working hard to understand what policies and programs can alleviate urban heat islands as part of larger policy,” says Madhavan. “Understanding the data is the first step towards change.
The second step is knowing where to channel funding. Research shows that planting trees in low-income, nonwhite communities can begin reducing the inequities related to tree cover, heat, and energy bills. The simple act of planting trees has an impressive capacity to mitigate climate change, improve inequities, and boost wellbeing.