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Urban Heat Island effect in Boulder

Updated: May 24, 2021

The City of Boulder needs to walk the talk on fighting climate change. Let's stop expanding the Urban Heat Island effect in Boulder.

The Urban Heat Island (UHI) effect arises when natural environments are replaced with artificial surfaces such as concrete and buildings, which absorb solar radiation differently. When nature is built on, the benefits of natural evaporative cooling and carbon absorption are lost. In addition, the heat produced directly by new human activity in the area (including transportation and air-conditioning) creates “islands” that are warmer than the surrounding areas -- an effect that has major adverse effects.

The Celestial Seasonings development (LUR2020-00063) as proposed will strengthen the UHI effect in this part of Gunbarrel and accelerate climate change. The developers will cut down mature trees and dig up the entire parcel and then pave parking lots, sidewalks, and wider streets. Most of the land that's left will become buildings (siding and rooftops). A few new small trees and a plot of grass will not compensate for the UHI effect all this development will bring to the neighborhood.

Comparable developments have recently been built in this area: Gunbarrel Center, Boulder View, Apex, and Diagonal Crossing. Then add the construction at 30th and Pearl and the planned Odell Place and Waterview developments and you can see Boulder is on a building spree. The UHIs are adding up.

UHIs are a serious problem here in Colorado. Denver has one of the most intense UHI effects in the nation, making summers for Denverites hotter and keeping the city unseasonably warm during the winter. As you’ve probably noticed, “Denver has faced rising temperatures, a record 75 days above 90 degrees this year, with projections showing 20 to 35 days a year topping 95 degrees by 2050.” 4 This is unfortunate given that heat-related illnesses are the number one killer of people from natural disasters, more than all others combined.


Despite being fairly close to Denver, the open space around Boulder allows it to cool off better. However, as suburbs keep sprawling and natural vegetation and soil are paved over, Boulder will heat up more. Boulder averages about four days per year when the heat index reaches at least 90 degrees. However, if Boulder responds slowly to curbing climate change, we can look forward to 27 days above 90 degrees by mid-century 1. Even more concerning, as Boulder works to be a racially sensitive city, the UHI effect deepens the racial divide. Yes, communities of color and low-income individuals suffer more from the UHI effect. UHIs create ideal conditions for formation of smog, which acts as a heat-trapping barrier, concentrating polluted air, and Black Americans in particular are more likely to have preexisting conditions that are exacerbated by heat and air pollution. And if all that is not enough, Black, Native, and Latinx Americans are more likely to be uninsured than other populations, making them less likely to receive adequate health care 5 .


Here's what this comes down to: Every piece of natural land lost exacerbates the UHI effect. Wherever roofs and pavement replace natural vegetation and soil, we contribute to this problem. The Celestial Seasonings proposal sprawls onto undeveloped land that now supports a vibrant wildlife population and protects against the UHI effect. This ultra-high density development will bring man-made heat and congestion to these parcels, as well as to roads and neighborhoods nearby. Boulder should not break new ground, especially when many locations in Boulder need to be redeveloped. Sustainability and climate sensitivity tell us to not build on natural places, but reuse areas we have already disturbed. We have a responsibility to future generations and to our minority population to be smarter in our development decisions. For Boulder to continue to be one of the most coveted places to live, we need to be careful how we use our scarce land resources. Gunbarrel needs a sub-community plan immediately before any high intensity projects are considered. The Celestial Seasonings proposal, LUR2020-00063, should be shelved for the time being. THANK YOU SO MUCH! WE ARE ALL IN THIS TOGETHER!

Email GCA Board members with any additional comments, suggestions and questions

Kit Fuller, Wanda Fuller

Julie Dye, April Lyons

Ardith Rietema, Rod Rietema

Mike Chiropolos– Counsel


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