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 City’s 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

6. 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

7. Heat Island Humor

8. 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

10. 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

11. 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

12. 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 Changing Paved Surfaces

13. 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.

15. 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

16. 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 Cool Tree Strategy

17. 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.

18. Contact Information • dhitchcock@harc.edu • http://www.harc.edu/coolhouston • David Hitchcock, AICP • 4800 Research Forest Drive • The Woodlands, Texas 77381 • 281-364-4007