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Urban Heat Island Urban Heat Island Mitigation and Air Mitigation and Air

QualityQuality

David Hitchcock, AICPDavid Hitchcock, AICP

Houston Advanced Research CenterHouston Advanced Research Center

August 2004August 2004

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Heat Island PremisesHeat Island Premises

Urban climates are Urban climates are altered significantly.altered significantly.

• TemperatureTemperature• Soil moistureSoil moisture• Cloud coverCloud cover• LightningLightning• RainfallRainfall• Planetary boundary layerPlanetary boundary layer

Urban climates can be Urban climates can be changed to mitigate these effects.changed to mitigate these effects.

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Current Heat Island Current Heat Island ChallengesChallenges

Can we model/simulate adequately? Can we model/simulate adequately? For example, sufficient for SIP purposes.For example, sufficient for SIP purposes.

What levels of change are need to make a What levels of change are need to make a difference?difference?

Since it takes 10 years or more to achieve Since it takes 10 years or more to achieve change, what can we do now as a “no change, what can we do now as a “no regrets” strategy? regrets” strategy?

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Modeling ChallengesModeling Challenges

Regulatory framework for modelingRegulatory framework for modeling Models not designed to capture change in Models not designed to capture change in

urban climateurban climate Meteorological modeling criticalMeteorological modeling critical Models at low resolution fail to capture Models at low resolution fail to capture

heat island mitigationheat island mitigation Land use/land cover becomes new critical Land use/land cover becomes new critical

issueissue Long time for transition to new modelsLong time for transition to new models

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Creating a Plan Creating a Plan to Change a City’s Climateto Change a City’s Climate

10th largest region in the U.S.10th largest region in the U.S. 4.7 million people4.7 million people 7,100 mi7,100 mi22 CMSA CMSA 1,400 mi1,400 mi22 urbanized area urbanized area Urbanized 200 square miles 1990 to 2000Urbanized 200 square miles 1990 to 2000 2.5% annual population growth2.5% annual population growth 30 to 40 square miles urbanized/year30 to 40 square miles urbanized/year

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Changing the ClimateChanging the Climate

Changing urban climates means changing the Changing urban climates means changing the urban fabric to:urban fabric to:

• more reflective, less heat absorbing materialsmore reflective, less heat absorbing materials• added vegetation for its cooling effectsadded vegetation for its cooling effects

Altering the urban fabric in ways that:Altering the urban fabric in ways that:• decrease heat absorbing properties of citiesdecrease heat absorbing properties of cities• increase their cooling capabilitiesincrease their cooling capabilities

ChangingChanging• urban fabric physicsurban fabric physics• the role of waterthe role of water

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Heat Island HumorHeat Island Humor

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What is Enough?What is Enough?

How can we possibly change surface How can we possibly change surface characteristics of a region this large?characteristics of a region this large?

• Substantial increase in tree cover - millions of Substantial increase in tree cover - millions of trees!trees!

• Changes to millions of rooftopsChanges to millions of rooftops• Changes to thousands of miles of paved roadways Changes to thousands of miles of paved roadways

and square miles of paved surfacesand square miles of paved surfaces

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Key Elements for ChangeKey Elements for Change

Identifying areas susceptible to changeIdentifying areas susceptible to change

Critical decision pointsCritical decision points

Actions affecting massive, incremental Actions affecting massive, incremental changeschanges

Picking control points for plan componentsPicking control points for plan components

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Cool Paving ExampleCool Paving Example

Little interest in surface reflectivity among Little interest in surface reflectivity among decision makersdecision makers

• Public works officialsPublic works officials• Transportation plannersTransportation planners• Building ownersBuilding owners

Public vs. private surfacesPublic vs. private surfaces Street surfaces vs. parking surfacesStreet surfaces vs. parking surfaces State versus local surfacesState versus local surfaces

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Timing FactorsTiming Factors

Well-constructed residential streets usually not Well-constructed residential streets usually not resurfaced over a 15-35 yr. time period resurfaced over a 15-35 yr. time period

Major highways and urban arterials resurfaced Major highways and urban arterials resurfaced or rebuilt within 10 to 15 years due to extensive or rebuilt within 10 to 15 years due to extensive use or expansion of a roadway. use or expansion of a roadway.

Many parking lots resurfaced - 5 to 10 yearsMany parking lots resurfaced - 5 to 10 years Residential driveways are infrequently Residential driveways are infrequently

resurfaced or replaced resurfaced or replaced Sidewalks infrequently resurfaced or replacedSidewalks infrequently resurfaced or replaced

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Changing Paved SurfacesChanging Paved Surfaces

Areas most susceptible to Areas most susceptible to changechange

Parking lotsParking lots New paved streetsNew paved streets

Critical decision pointsCritical decision points Parking lot surface Parking lot surface

decisions of owner/ decisions of owner/ managers and paving managers and paving companies - price drivencompanies - price driven

Roadways decisions driven Roadways decisions driven by government standards by government standards and practices.and practices.

Massive change through Massive change through incremental, predictable incremental, predictable paths:paths:

Over 10 year period, new Over 10 year period, new paved roadways account paved roadways account for 10% of all paved for 10% of all paved surfacessurfaces

Parking surfaces make up Parking surfaces make up 60% of the paved surfaces 60% of the paved surfaces resurfaced every 5-10 yrsresurfaced every 5-10 yrs

Maintenance opportunities Maintenance opportunities on roadwayson roadways

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Decision PointsDecision Points

Control pointsControl points Parking lotsParking lots

• building owners and managers • paving companiesbuilding owners and managers • paving companies• local government regulationslocal government regulations

New roadwaysNew roadways• Local government standards and development practices – Local government standards and development practices –

public workspublic works• State government standards and practices – State DOTState government standards and practices – State DOT

StrategyStrategy• Product awareness for owners and paving companiesProduct awareness for owners and paving companies• Regulatory change for parking lots • combine with landscape Regulatory change for parking lots • combine with landscape

requirementsrequirements• Performance standards change to include reflectivityPerformance standards change to include reflectivity

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Trees/VegetationTrees/Vegetation

Trees play a substantially different role in Trees play a substantially different role in modeling and in the community.modeling and in the community.

Trees are not routinely “changed” over a Trees are not routinely “changed” over a 10 year period.10 year period.

Mostly a declining inventory.Mostly a declining inventory. Decisions points are different and less Decisions points are different and less

identifiable.identifiable. Strategy is more complex. Strategy is more complex.

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Trees and Air QualityTrees and Air Quality

Role of TreesRole of Trees Biogenic emissionsBiogenic emissions Shade and energy benefitsShade and energy benefits Landscape effects - maintenance emissionsLandscape effects - maintenance emissions Cooling effectsCooling effects Widespread community support for treesWidespread community support for trees Widespread community support for Widespread community support for

development that removes treesdevelopment that removes trees

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Cool Tree StrategyCool Tree Strategy

ConservationConservation33

Incremental tree impacts Incremental tree impacts for SIPfor SIP

• Ozone depositionOzone deposition

• Shade tree energy Shade tree energy benefitsbenefits

• Offset for lawn and garden Offset for lawn and garden emissionsemissions

• Heat island benefitsHeat island benefits

Public works set asides Public works set asides for treesfor trees

Public sector leadershipPublic sector leadership

Capture private sector Capture private sector actions!actions!

• Web-based credit systemWeb-based credit system

• Web-based tracking and Web-based tracking and salesale

• Region wide tree planting Region wide tree planting initiativesinitiatives

• Supply issueSupply issue

Public sector financingPublic sector financing Public/private Public/private

partnerships coalitionspartnerships coalitions

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ConclusionsConclusions

There are systematic, cost effective actions to alter There are systematic, cost effective actions to alter an urban fabric.an urban fabric.

Heat island mitigation components, such as cool Heat island mitigation components, such as cool roofing and trees, provide a stream of benefits than roofing and trees, provide a stream of benefits than can be tapped to change an urban climate.can be tapped to change an urban climate.

The scope and amount of time required for such The scope and amount of time required for such changes is as short as 10 years.changes is as short as 10 years.

Focus and continuity of effort are essential to Focus and continuity of effort are essential to achieve many of the strategies set forth here.achieve many of the strategies set forth here.

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Contact InformationContact Information

dhitchcock@harc.edudhitchcock@harc.edu http://www.harc.edu/coolhoustonhttp://www.harc.edu/coolhouston

David Hitchcock, AICPDavid Hitchcock, AICP 4800 Research Forest Drive4800 Research Forest Drive The Woodlands, Texas 77381The Woodlands, Texas 77381

281-364-4007281-364-4007