Trees are part of the targeted responses needed to mitigate high urban heat; the New York Times reported a 31-degree temperature difference on a hot day between neighborhoods with and without heat-mitigating vegetation and shade. Microclimates within cities reflect neighborhood differences due to the imbalance of impervious surfaces like pavement compared to trees and other vegetation. Other factors include housing quality, traffic patterns and proximity to industrial sites. Unfortunately, this is linked to race and ethnicity; an Environmental Protection Agency review of prior research found that the neighborhoods with highest temperatures are disproportionately those where low-income individuals and people of color reside. Research has also shown wealthier neighborhoods have lower temperatures during extreme heat events because they have more trees and vegetation, which produces a cooling effect.
Chattanooga, Tenn., is one city that puts a particular emphasis on greening with an environmental justice lens. City officials unveiled their Climate Action Plan earlier this year, highlighting economic and health risks if climate challenges are not addressed. Anchoring the Climate Action Plan to economic growth and prosperity, Mayor Tim Kelly points to the city’s thriving outdoor culture and green economy as a major advantage.
Chattanooga’s pursuit of ambitious climate action goals involves utilizing technology and mapping to expand tree canopies and green spaces. GIS provides the foundation for forestry decision-making. According to Brendan Cleary, Chattanooga’s GIS systems and database manager, the city benefits from a partnership with The Lyndhurst Foundation that has supported geospatial research at the University of Tennessee’s Interdisciplinary Geospatial Technology (IGT) Lab. A public story map called City of Trees now enables officials to compare canopy cover with spatial equity.
Recently, the re-established parks department and urban forestry program faced challenges in identifying tree locations and assessing their conditions. They asked the IGT Lab to help map the city’s trees to make Chattanooga “A City Within a Park” through a connected network of outdoor spaces. According to Cleary, they recently accomplished the first critical step: getting an inventory of trees and their relationship with the public right of way using lidar and drone aerial photos. Those analytic efforts are supported by a community engagement component, with residents uploading photos onto the GIS platform.
Where trees can be feasibly planted and how that affects equity and temperature requires multiple layers of data. In addition to the presence or absence of green areas, relevant information that should be mapped includes temperatures, the location of shade-providing physical structures like bus shelters, along with data on health consequences, flood zones and more. All these factors will help the city make better decisions concerning where and what type of tree to plant and their impact on extreme heat.
Other cities also provide examples of best practices in using technology to optimize urban forests. Singapore’s TreesSG maps show nearly every tree in the city. The database facilitates the monitoring of tree growth, so it is easy to manage trimming, monitor tree health, and determine climate and health benefits hyperlocally. In 2015, New York City created a visual image of trees on each street as part of its TreesCount! urban forestry census initiative. And, as featured in my 2016 article “How D.C. Grew a Data-Driven Tree Strategy,” the district used lidar to coordinate and map forestry care.
The need for trees and green spaces will continue to accelerate as global temperatures rise. Unfortunately, cities have limited resources for trees and green areas, and thus investments should be made where they do the most good. Satellite maps and drone information help identify gaps, and layering spatial visualizations pinpoints demographic inequities related to tree canopies and heat-aggravated illnesses. Digital insights help cities maintain green areas and produce a more attractive, healthy and climate-adapted environment.
This story originally appeared in the December issue of Government Technology magazine. Click here to view the full digital edition online.
