Toward a Cool City
By Lily Auliff

Planting 15 million trees and using light-colored coatings on all roofs and roadways could cool parts of Houston by up to four degrees and cut ground level ozone smog concentrations by five percent, according to preliminary modeling from Lawrence Berkeley National Laboratory (LBNL).

Reducing Houston’s Heat Island, a study funded by Houstonians Bill and Andrea White through The Park People, addresses a phenomenon known as the urban heat island (UHI). Urban areas in Houston can be 3 to 5 degrees warmer than the surrounding countryside; this increased temperature accelerates ozone formation and raises energy use.

Ground level ozone smog is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight. Although NOx and VOCs are released year round, the area’s ozone season runs from March to November, when temperatures are warmest.

“My ultimate goal is to make Houston a lot greener and cool down the city, reduce utility bills, and reduce pollution,” says Bill White, who is president and CEO of the Wedge Group and on the board of the Greater Houston Partnership. White eventually would like to see UHI reduction strategies more fully explicated in the region’s State Implementation Plan (SIP) to reduce ground level ozone.

Cooler and Cleaner
To mitigate the UHI effect, the report advocates planting trees and resurfacing roads, parking lots, and roofs. Trees both shade and cool the air through evapotranspiration, a process where plants absorb water from the ground and release it from their leaves into the air. Lighter colored, reflective pavements and rooftops have lower surface temperatures and absorb less heat than their darker counterparts.

According to the report, reducing the UHI effect can improve air quality by:

• Slowing the rate of temperature-dependent, smog producing photo chemical reactions;
• Decreasing temperature-dependent VOC emissions from vegetation and other biological sources;
• Reducing the evaporative losses of VOCs, such as gasoline, solvents, and paints from mobile and stationary sources; and
• Decreasing the need for cooling energy, generating capacity, and ultimately NOx emissions from power plants.

The Scenarios
The preliminary modeling done by the LBNL outlines four scenarios for the Houston region: a base case scenario that represents business as usual, and three scenarios with increasing levels of UHI mitigation.

In the first mitigation scenario, 60 percent of roofs and pavements are modified and 4 million trees are planted, which results in a maximum temperature reduction of two degrees Fahrenheit. Mitigation Scenario 2 calls for modifying 100 percent of the area’s roofs and pavements and planting 15 million trees. Mitigation Scenario 3 is identical to Scenario 2, except it accounts for increases in VOC emissions from the added vegetation. The last two scenarios would result in up to a four-degree temperature drop, according to the models.

Into the SIP
The SIP makes mention of temperature reduction efforts in the Voluntary Mobile Emissions Reduction Program (VMEP) section. White, however, would like to see it integrated in more quantifiable ways.

The current version of the SIP, which must be approved or disapproved by the U.S. Environmental Protection Agency (EPA) by October 15, stills falls short of the emissions reduction requirements. To make up for this gap, the region must specify further controls at a later date.

“If there’s still a gap and there is sufficient funding and community will, then this is a way of closing that gap,” suggests White. “If other means are found of closing the gap, then it can be something that is funded by an emissions trading scheme.”

Through emissions trading, industry or other polluters would be allowed to purchase emissions credits, perhaps by planting trees or resurfacing roofs and pavement, to make up for reductions that they find difficult or too expensive to make. This implementation strategy comes with its own funding to cool, clean, and beautify the region, points out White.

Quantifying UHI mitigation well enough for the SIP may be easier said than done, however.

Lily Wells, Chief Air Quality Planner at the Houston-Galveston Area Council (H-GAC) who is charged with organizing the VMEP program, supports White’s activities, but notes that the LBNL results are not yet suitable for implementation into the SIP.

Future Research
White understands that the LBNL modeling was just the beginning. “At first when I described cooling down Houston, people thought it sounded like science fiction,” recalls White. “So, I felt that before I could do anything and ask people to climb on board, I had to get a significant science basis that we could cool down our city and clean our air. With that in hand, I was able to approach a wide variety of people and organizations to climb on board.”

An eclectic group has endorsed White’s efforts, including Houston Mayor Lee P. Brown, the Greater Houston Partnership, the Business Coalition for Clean Air, Sierra Club, Environmental Defense, and the AFL-CIO.

“The study was really a visible catalyst,” says Dr. Joseph Romm of the Center for Energy & Climate Solutions, which helped facilitate the research. Romm acknowledges that many leaders in Houston had individually considered UHI mitigation. But, he explains, “What there hadn’t been before this work was all of the players with knowledge and the ability to influence policy talking to one another, so that they could come to some consensus.”

The efforts in Houston to put UHI mitigation into the SIP has sparked EPA action as well. “We have not given SIP credit as an agency to any other city for a cool city effort, but it is something we are looking into,” explains Jack Edwardson, Associate Director of the Air Quality Division of EPA’s Office of Air Quality Planning and Standards.

EPA is working to improve the LBNL data and determine if it is suitable to integrate into the SIP. “We have certain concerns about that actual data that went into this study and some of the modeling approaches that were taken,” adds Edwardson. “We now have modelers that are working with LBNL to try to beef up the study.”

A subcommittee of H-GAC’s Regional Air Quality Planning Committee has also begun meeting to bring all regional stake holders to the table for discussion of a unified heat island strategy. Facilitated by the Gulf Coast Institute, the group includes White, Dr. Pamela Berger of the Mayor’s Office, David Hitchcock of the Houston Advanced Research Center, Mickey Merritt of the Texas Forest Service, Dr. Doug Lipka of the Houston EPA lab, Victoria Herrin from the City’s Planning Department, Gary Woods of the Urban Forest Council, and several others. The group will hold a heat island workshop with EPA October 18-19.

A variety of strategies will be considered, including public education on the merits of light-colored roofing, city and county building code changes, incentives for developers, and public funding of trees and open space, says White.