Urban Heat Island Mitigation and Air Quality

1
Urban Heat Island Mitigation and Air Quality

• David Hitchcock, AICP
• Houston Advanced Research Center
• August 2004

2
Heat Island Premises

• Urban climates are altered significantly.
• Temperature
• Soil moisture
• Cloud cover
• Lightning
• Rainfall
• Planetary boundary layer
• Urban climates can be changed to mitigate these
  effects.

3
Current Heat Island Challenges

• Can we model/simulate adequately? For example,
  sufficient for SIP purposes.
• What levels of change are need to make a
  difference?
• Since it takes 10 years or more to achieve
  change, what can we do now as a no regrets
  strategy?

4
Modeling Challenges

• Regulatory framework for modeling
• Models not designed to capture change in urban
  climate
• Meteorological modeling critical
• Models at low resolution fail to capture heat
  island mitigation
• Land use/land cover becomes new critical issue
• Long time for transition to new models

5
Creating a Plan to Change a Citys Climate

• 10th largest region in the U.S.
• 4.7 million people
• 7,100 mi2 CMSA
• 1,400 mi2 urbanized area
• Urbanized 200 square miles 1990 to 2000
• 2.5 annual population growth
• 30 to 40 square miles urbanized/year

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Changing the Climate

• Changing urban climates means changing the urban
  fabric to
• more reflective, less heat absorbing materials
• added vegetation for its cooling effects
• Altering the urban fabric in ways that
• decrease heat absorbing properties of cities
• increase their cooling capabilities
• Changing
• urban fabric physics
• the role of water

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Heat Island Humor
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What is Enough?

• How can we possibly change surface
  characteristics of a region this large?
• Substantial increase in tree cover - millions of
  trees!
• Changes to millions of rooftops
• Changes to thousands of miles of paved roadways
  and square miles of paved surfaces

9
Key Elements for Change

• Identifying areas susceptible to change
• Critical decision points
• Actions affecting massive, incremental changes
• Picking control points for plan components

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Cool Paving Example

• Little interest in surface reflectivity among
  decision makers
• Public works officials
• Transportation planners
• Building owners
• Public vs. private surfaces
• Street surfaces vs. parking surfaces
• State versus local surfaces

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Timing Factors

• Well-constructed residential streets usually not
  resurfaced over a 15-35 yr. time period
• Major highways and urban arterials resurfaced or
  rebuilt within 10 to 15 years due to extensive
  use or expansion of a roadway.
• Many parking lots resurfaced - 5 to 10 years
• Residential driveways are infrequently resurfaced
  or replaced
• Sidewalks infrequently resurfaced or replaced

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Changing Paved Surfaces

• Areas most susceptible to change
• Parking lots
• New paved streets
• Critical decision points
• Parking lot surface decisions of owner/ managers
  and paving companies - price driven
• Roadways decisions driven by government standards
  and practices.

• Massive change through incremental, predictable
  paths
• Over 10 year period, new paved roadways account
  for 10 of all paved surfaces
• Parking surfaces make up 60 of the paved
  surfaces resurfaced every 5-10 yrs
• Maintenance opportunities on roadways

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Decision Points

• Control points
• Parking lots
• building owners and managers paving companies
• local government regulations
• New roadways
• Local government standards and development
  practices public works
• State government standards and practices State
  DOT
• Strategy
• Product awareness for owners and paving companies
• Regulatory change for parking lots combine with
  landscape requirements
• Performance standards change to include
  reflectivity

14
Trees/Vegetation

• Trees play a substantially different role in
  modeling and in the community.
• Trees are not routinely changed over a 10 year
  period.
• Mostly a declining inventory.
• Decisions points are different and less
  identifiable.
• Strategy is more complex.

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Trees and Air Quality

• Role of Trees
• Biogenic emissions
• Shade and energy benefits
• Landscape effects - maintenance emissions
• Cooling effects
• Widespread community support for trees
• Widespread community support for development that
  removes trees

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Cool Tree Strategy

• Conservation3
• Incremental tree impacts for SIP
• Ozone deposition
• Shade tree energy benefits
• Offset for lawn and garden emissions
• Heat island benefits
• Public works set asides for trees
• Public sector leadership

• Capture private sector actions!
• Web-based credit system
• Web-based tracking and sale
• Region wide tree planting initiatives
• Supply issue
• Public sector financing
• Public/private partnerships coalitions

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Conclusions

• There are systematic, cost effective actions to
  alter an urban fabric.
• Heat island mitigation components, such as cool
  roofing and trees, provide a stream of benefits
  than can be tapped to change an urban climate.
• The scope and amount of time required for such
  changes is as short as 10 years.
• Focus and continuity of effort are essential to
  achieve many of the strategies set forth here.

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Contact Information

• dhitchcock_at_harc.edu
• http//www.harc.edu/coolhouston
• David Hitchcock, AICP
• 4800 Research Forest Drive
• The Woodlands, Texas 77381
• 281-364-4007