City of Boulder plans to use CU Boulder data to study the effect of trees on urban heat for climate-mitigation planning

The city of Boulder and researchers at the University of Colorado Boulder have joined forces to document and attempt to mitigate the urban heat island effect.

The urban heat island effect is when dense urban areas are hotter than nearby rural or suburban areas. This effect, according to previous research, stems from the higher density of impervious surfaces—such as concrete and asphalt—in cities, which store more heat and retain less moisture, thus generating higher surface and air temperatures. 

This, in turn, can mean more energy is needed to cool buildings, a decreased quality of life for citizens, and even consequences for the surrounding landscape. 

By deploying specially protected thermometers throughout Boulder, researchers hope to gather data on how trees and vegetation can possibly reduce that urban heat. The city then plans to use the data for climate-mitigation planning as part of its Cool Boulder initiative, a long-term community-led climate campaign. 

“We are very excited to work with CU on this critical research, which will help inform a range of policies and programs—from expanding urban forests to reducing impervious surfaces and experimenting with more reflective surfaces,” said Brett KenCairn, Boulder’s senior policy advisor for climate, sustainability and resilience. “Having this sort of applied research partner is vital in helping us rapidly develop climate risk reduction strategies.”

While the city of Boulder has more trees than most cities, as other CU Boulder research has found, efforts to understand patterns of heat in relation to vegetation can help scientists better understand how the urban microclimate functions, the researchers say.

Laura Dee, CU Boulder assistant professor of ecology and evolutionary biology, leads a group of researchers who aim to evaluate and better understand how to reduce the effects of the urban heat island in the city of Boulder, in ways that enhance biodiversity and provide other benefits to human well-being from nature. 

Meghan Hayden, a PhD student and Rebecca McHugh (a bachelor’s accelerated master’s student) in Dee’s laboratory coordinated the researchers’ efforts to place 75 temperature sensors at various spots throughout Boulder—ranging from residential areas to industrial, public and businesses—to monitor temperature by cataloging the air temperature once per minute. The researchers were also careful to pick locations that include a diverse array of tree cover—many of which are also part of the Boulder Apple Tree Project and the Environmental Justice zones. 

At the same time, the team is working with a group at NASA’s Jet Propulsion Laboratory to validate land temperatures sensed from ECOSTRESS (the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station). 

ECOSTRESS measures the temperature of plants to address three scientific questions: how the biosphere responds to changes in water availability; how changes in water stresses affect the global carbon cycle; and whether agricultural vulnerability can be reduced through better monitoring and drought forecasts. 

“Escalating summer temperature extremes are unfortunately an inevitable part of our future,” said KenCairn. “We must move quickly to develop a baseline understanding of the heat dynamics of the community now and how these will intensify as climate change advances.”

The sensor installation was completed in early June, and the sensors will be removed in October. 

Learn more about the Urban Heat Boulder project at its website. And see this site to learn more about the Cool Boulder initiative. 

Header photo is of Pearl Street Mall in Boulder and is courtesy of the city of Boulder.