October 11, 2008

More Trees Could Cool Tucson’s Parking Lots


In the vast, hot asphalt lots of our commercial culture, the driver who snags a spot under a lonely, scraggly shade tree just about whoops in triumph.

Tucson officials want to hear that sound more often, in parking lots that are greener and cooler than today's.

They're pushing a city ordinance to require developers of virtually all new non-residential projects to more than double the concentration of trees in parking lots.

The proposal, scheduled for a hearing next month, would raise the bar from one tree for every 10 parking spaces to one tree for every four spaces.

The proposal's effect would be sweeping. Most non-single-family- home developments with more than four parking spaces would be covered.

That includes apartment complexes, churches, offices, industries and shopping centers.

All that's left out are parking lots owned by car dealers, which are considered showrooms and treated differently because so much of the parking space is filled by cars for sale.

City officials want to fight the urban heat-island effect, explained Irene Ogata, the city's urban-landscape manager.

That's the well-documented phenomenon in which rising air temperatures in Tucson and many other cities are linked to hotter concrete, asphalt and other hard surfaces.

Ogata said research from the Sacramento, Calif., area shows trees in parking lots reduced summertime air temperatures by 1.8 to 3.6 degrees. Parking lots, a U.S. Forest Service report says, are thermal hot spots and miniature heat islands.

The city's idea isn't making everyone whoop with joy, however.

A leader of a group of commercial developers in Tucson said he is open to such a proposal, but he won't take a position without knowing more specifics.

"The devil is in the details," said David Pittman, director of the Arizona Builders Alliance.

"Frankly, you drive around town, you see these parking lots that have 100 spaces, only 30 percent are being used on most days," Pittman said. "They build the parking lots for the Christmas season, which is the only time they are all full. A lot of people don't think that makes a lot of sense."

A Tucson Metropolitan Chamber of Commerce official pointed out that more trees would require more water - at the same time the city is preparing to require that business developers use harvested rainfall to handle a significant percentage of their outdoor water needs. The rainwater ordinance, which is separate from the parking- lot-landscaping proposal, goes before the City Council on Oct. 14.

"It's kind of the domino effect. Everything is connected," said Robert Medler, the chamber's government-affairs manager. "If they pass this parking-lot proposal, that will change the irrigation demand we've been working on."

To developers concerned about having to use more water for more trees, Ogata said the city code already requires that trees in such parking lots must be low-water-use varieties.

Typically, there is no problem getting enough parking-lot water for trees, whether the requirement is one tree for four parking spaces or for 100 spaces, said Ann Audrey, the city's environmental- projects coordinator.

"Say you have a Wal-Mart and it is 5 percent landscaping, and 95 percent roof and parking lot," Audrey said. "There's a lot of water that runs off parking lots."

A National Weather Service official who has studied the heat- island effect likes the proposal for more trees.

"Anything you can do, it's good to have more trees out there, and take more CO2 out of the atmosphere," said meteorologist John Glueck, referring to a separate theory that carbon dioxide and other greenhouse gases are slowly raising global temperatures. Trees take in carbon dioxide emitted by power plants, cars and other sources.

The heat-island effect has raised Tucson's nighttime temperatures by 2 to 3 degrees in the past 30 years, Glueck said.

Nobody knows how many parking lots exist in Tucson. But in general, they occupy 10 percent of the land in U.S. cities, and 20 percent to 30 percent of downtown areas, the Forest Service report says.

In unincorporated areas of Pima County, county officials have required greener lots - with one tree for every four spaces - in new developments since 2003. In some newly developed areas, the contrast with lots in city shopping malls is dramatic.

Along La Cholla Boulevard near River Road, for instance - not far north of the Tucson city limits - the parking lots for a shopping, office and medical complex feature trees closely bunched both along the edges and in the interior.

An infrared map that Arizona State University researchers prepared a few years ago makes the link explicit between heat and parking-lot pavement, Ogata said.

It shows the Tucson area's hottest spots in yellow. Inside or closely bordering yellow areas were three of the region's four big shopping malls - El Con, Tucson and Foothills - along with Tucson International Airport. Interstates 10 and 19 are shown as yellow lines.

Trees make a difference, helping to shade parking lots' dark surfaces, Ogata said.

"They transpire and breathe, like a swamp cooler, and let off a percentage of their moisture into the air. The moisture cools things."

Shade trees planted at parking lots "transpire and breathe, like a swamp cooler, and let off a percentage of their moisture into the air. The moisture cools things."

Irene Ogata

Tucson urban-landscape manager


Pima County might reduce parking requirements for shopping centers. Read the details in Monday's Star.


* What: Public hearing on an ordinance requiring parking lot trees, held by the Tucson Planning Commission.

* When: 7 p.m. Nov. 5.

* Where: City Hall's City Council Chambers, 250 W. Alameda St.


Research has shown that:

* Planting 100 trees in six cities, including Glendale, Ariz., removed anywhere from 87 to 1,014 tons of various air pollutants.

* Ground-surface temperatures in shaded lots in Davis, Calif., were up to 36 degrees cooler than in unshaded lots, and vehicle interior temperatures were 47 degrees lower in shaded lots.

* Six million trees in Sacramento County, Calif., remove more than 1,600 tons of air pollution annually, mainly ozone and small particles linked to respiratory disease.

* A fuel tank in a shaded parking lot in Davis was 3.6 to 7.2 degrees cooler than in an unshaded lot.

* Shading streets with trees in Modesto, Calif., stretched the street life by reducing pavement fatigue rutting, cracking and other distress.

Sources: U.S. Forest Service and Journal of Arboriculture

* Contact reporter Tony Davis at 806-7746 or [email protected]

Originally published by TONY DAVIS, ARIZONA DAILY STAR.

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