graphic trees in Scottsdale

This graphic, part of the study of heat and trees in Scottsdale, compares income in various neighborhoods with the amount of shade and subsequent average temps.

Some of Scottsdale’s hotter neighborhoods are also its poorest, according to a heat mitigation study by the city and Arizona State University.

The three-year study, presented to City Council last week, shows land surface temperature decreases by more than a degree Fahrenheit in neighborhoods for each $10,000 increase in mean per capita income. 

“We did find, as is evident in cities all across the United States, especially the Southwest, this tight coupling of income and land surface temperatures,” said ASU Associate Professor David Hondula from the School of Geographical Sciences and Urban Planning. 

“Perhaps it’s no surprise that places in Scottsdale, where the average household has lower income have higher land surface temperatures,” Hondula said. “It’s a pretty tight coupling for Scottsdale, similar to what we’ve seen in regional and national analysis.”

He said the findings have implications for future efforts to adapt to climate change.

“I think this presents an important challenge for the sustainability process to continue,” he said. “Places that might be prioritized for cooling are also the places where residents may be least likely be able to afford or implement some of the important cooling strategies.”

Trees cool down their surroundings and poorer neighborhoods simply have less vegetation. 

One of the biggest reasons for that is the either real or perceived cost of water, Hondula said, explaining that older development designs also provide very little opportunity for tree planting and tend to contain more blacktop.  

“We do see this tension between new development and existing infrastructure,” Hondula said. “I think it’s a pretty safe bet that a lot of new development that’s happened, even development that’s occurred in the past five or 10 years, is cool.” 

Hondula noted some codes “require a certain amount of the landscape to be reflective or have trees or other desired cooling properties.”

“Existing infrastructure is a real thorn in our side when thinking about how we can become cooler and the places we focused on in this project, the growth areas, already have a lot of existing infrastructure,” he said. 

Mayor David Ortega noted that regulations requiring developers to plant and maintain trees have been on the books for 50 years.

But how closely those regulations are enforced appears to be a different story.

“We don’t have at this time an active enforcement group to go out and cite them,” Scottsdale Environmental Initiatives Manager Tim Conner said. “We do have code enforcement but they are doing other things than looking for trees in parking lots.”

Councilwoman Solange Whitehead called for more enforcement of the rules. 

Of the 20 hottest areas in metropolitan Scottsdale, 19 were located in the southern half of the city – specifically, a 4.2-mile, largely residential area south of McDowell and west of Hayden roads. 

Tree density is approximately half in this area of the city’s greenest neighborhoods. 

In the meantime, the Indian Bend Wash appears to be the coolest part of town. It is about 2 degrees Fahrenheit to 3 degrees Fahrenheit cooler than surrounding neighborhoods. What is not known yet is if that cooling effect from the vegetation in the wash affects other areas when the wind blows. 

The city’s growth areas in general are hotter than the rest of the city, according to the report.

Scottsdale’s average summer temperature is 122.5 degree Fahrenheit, while the average temperature is 129 degrees Fahrenheit at the Airpark, 129.5 degrees Fahrenheit in Old Town and 131.4 degrees Fahrenheit in South Scottsdale.

The report made three recommendations to mitigate heat in the city:

• Increase tree canopy, particularly along frequently traveled pedestrian walkways as well as the south and west facades of buildings. 

• Reduce the land area of exposed dark asphalt, dark roofs and other hot surfaces.

• Improve and increase pedestrian shade amenities through building-integrated and free-standing shade structures, particularly along frequently traveled walkways and in location that support public transportation. 

Information from the heat mitigation report will be included in the city’s sustainability report, which is expected to be finished in late summer or early fall 2022.