Cities look for solutions to ‘urban heat island’ effect

A Climate Central study reports that, on average, U.S. cities were 2.4 degrees hotter than the surrounding rural areas during the past 10 summers, and Las Vegas topped the list of the most extreme heat islands at 7.3 degrees hotter.

The urban heat island effect is separate from climate change — it’s the result of higher temperatures in cities due to the abundance of blacktop and pavement. But climate change intensifies the effect by raising summer highs and more severe heat waves.

In U.S Cities. Cities are 2 degrees to 6 degrees warmer on average than their surroundings and are warming up to 50 percent faster than the rest of the country.

Urban Land Institute Nevada hosted “Scorched,” a panel discussion with national and local experts to discuss how Las Vegas can be a leader in combating heat island effect.

A report from the Urban Land Institute discussed at the panel explores how the land use, design, and real estate sectors are responding with design approaches, technologies, and new policies to mitigate the infrastructure impacts of extreme heat and to protect human health.

Officials said there are ways cities can minimize urban heat island effect like installing reflective “cool roofing” and planting trees. The City of Las Vegas, for instance, encourages the use of white and light-colored roofs on many of its buildings to mitigate the harmful effects of the city’s significant urban heat island effect. 

The Molasky Corporate Building in Las Vegas is the first commercial office in the city to incorporate a white material rooftop to ward off the heat island effect and a garden on the 7th floor, and while it does not have the same benefits as a green roof, the city argues it’s a better option for the city’s desert environment.

As part of the city’s “green infrastructure,” trees are planted strategically along walkways. The city of Las Vegas governs about 84,000 acres, tree canopies cover about nine percent (7,665 acres), but rising temperatures threaten even that coverage.

“We think there’s a lot of tree canopy that exists in Las Vegas today that probably isn’t going to survive these warmer temperatures,” said Tom Perrigo, Chief Sustainability Officer for the City of Las Vegas, adding that along with planting more trees the city will need to replace existing canopy with more heat resistant trees.

Panelists stressed that there is no “one size fits all” approach to extreme heat management. Local environment largely determines which strategies will be most effective and appropriate.

For instance, suburbs like Summerlin tend to be significantly cooler than the hearts of urban cities, and while these higher-income suburban districts have benefited from cooler temperatures due in part to more vegetation there is a significant cost.

“Believe me when I tell you were well aware of the issue with turf in Summerlin, which is a huge consumer of water,” said Tom Warden, senior vice president of community and government relations in Summerlin. ”We do have decorative panels from earlier on in Summerlin and we even have some from more recent times. Those need to be replaced.”

Higher temperatures also exacerbate ground-level air pollution. In fact, heat islands are responsible for 20 percent of urban smog formation, according to the study, which tends to affect lower-income communities in the inner city.

Urban sprawl is a contributor to hotter cities and inefficient use of resources says Steffen Lehmann the director of the UNLV School of Architecture, adding that building codes around the country must be updated to create more compact cities.

“We need to build cities that are compact, mixed-use and walkable,” Lehmann said, “where you can comfortably live and work in the same neighborhoods.” City zoning and development has created long commutes and “created the problem we are in today,” not only urban heat islands but our dependence on cars, Lehmann said.

Perrigo says the 2020 master plan for the City of Las Vegas incorporates a number of mitigation strategies to address the changing climate including “compact urban centers.”

The City of Las Vegas increases high rise provisions to 75 feet, following the national model.

“That’s going to get us to that sweet spot of buildings that are three, four, five, six, seven stories high,” Perrigo said. “It wasn’t easy. We had a lot of opposition.”

While designing for extreme heat is an emerging issue and not yet mainstream in many U.S. cities, panelists argued that it’s likely to pick up momentum because of extreme heat increases, and developments that plan for extreme heat may gain a competitive advantage.

According to the Urban Land Institute study, research has shown extreme temperatures are likely to be linked to a decrease in U.S. GDP through reduced growth rates and increased expenses. The trends are visible at the country, state, and city scales across sectors including finance, retail, and construction.

Perrigo said it’s clear that in Las Vegas designing for temperature—even on a smaller scale like planting more trees or lessening heat-absorbing surfaces like blacktops—creates retail sales and raises property values.

“We are taking back some of that right of way,” he said. “We built the city with way too much right of way for cars. We are taking it back and giving it to people, and trees, and plants.”

Edited to clarify that the Molasky Corporate Building garden is on 7th floor patio an not on the rooftop.