Mitigation of the Urban Heat Island

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Mitigation of the Urban Heat Island

• Cameron Lee
• October 16, 2008

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Quick Review of the UHI Effects

• Increased Temperature caused by
• Pavement buildings absorbing heat emitting at
  night
• Buildings decrease sky view block wind
• Less evapotranspiration from reduced vegetation
• Concentrated anthropogenic heat release
• Some Effects of Warmer Urban Climate
• Uncomfortable living environment
• Heat related illness and death
• Increases in Ozone Concentration
• Harms humans and plant-life
• Further increases CO2
• Increase in Energy consumption
• Peak utility loads can increase up to 2 for
  every 1F increase

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Urban Heat Island in Atlanta, Georgia
Image from http//earthobservatory.nasa.gov/Newsr
oom/NewImages/images.php3?img_id17489
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Smog over Sao Paulo, Brazil

Smog over Sao Paulo, Brazil Photo by Gabriel de
Andrade Fernandes
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Two Types of Contributing Factors

• Un-controllable Variables
• Season
• Wind Speed
• Cloud Cover
• Diurnal Conditions
• Anti-Cyclone Conditions
• Controllable Variables
• Urban Design and Structure
• Air Pollutants
• Anthropogenic Heat

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Mitigating the UHI

• Different Routes to Take for Reduction
• Increase Green Areas in Cities
• Better Roofing Materials
• Cool Paving Materials
• Decreasing Air Pollutants
• Better Building Materials
• Better City Planning

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Increasing Green Areas in City

• Planting Trees on Sidewalks and by windows

• Building Urban Parks

Image from http//www.ohiosaf.org/urban2.jpg
Image from http//www.forestry.ky.gov/NR/rdonlyre
s/DC652BAA-D16C-4397-809C- 80ADDD03EC41/0/treesand
peoplearoundfountain.jpg
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Strategic Residential Tree Planting
Image from http//heatisland.lbl.gov/Vegetation/P
lanting.html
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Increasing Green Areas in City

• Benefits
• Practical and Inexpensive
• Lowers Energy Needs
• Provides Shade
• Increases Evapotranspiration
• Up to 40 gallons a day
• Up to a 300 increase
• Parks help return surface to a more natural
  albedo
• Helps to Control Runoff

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Better Roofing Materials

• Two Routes to take
• Cool Roofs
• Green Roofs
• Why so Popular?
• Relatively Inexpensive Practical
• Decreases heat Gain into buildings and lowers
  energy costs economical in the long run
• Enhances Roof Durability due to decreased UV
  exposure

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Cool Roofs

• Adding Bright White Layer to Rooftop
• Highly reflective
• Highly emissive
• Can cool roof to within 10F of air
• Reflects UV radiation to extend life of roof
• Lowers Energy Costs

Image from http//wakingmedia.com/savin/images/st
ories/Cool-roof.jpg
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Cool Roof Albedos
Image from http//heatisland.lbl.gov/CoolRoofs/He
atTransfer/Sunlight
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Energy Savings from Cool Roofs
Image from http//heatisland.lbl.gov/CoolRoofs/
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Green Roofs

• Intensive Roofs
• Have thick layers of soil
• 6 to 12 inches or more
• Can support trees, grass and plants
• Extensive Roofs
• Simpler green roofs
• Soil layer is 6 inches or less
• Supports grass and small plants

Image from http//en.wikipedia.org/wiki/Image200
80708_Chicago_City_Hall_Green_Roof.JPG
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Green Roofs

• Benefits
• Increases Evapotranspiration
• Decreases Heat Gain into buildings lowers
  energy costs
• Increases Shaded Areas

Image from http//en.wikipedia.org/wiki/ImageGre
en_Roof_at_VendC3A9e_Historial,_les_Lucs.jpg
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Cool Paving Materials

• Lighter Colored Materials
• High Solar Reflectance
• Come in shades of white, gray, and beige
• Using Concrete Instead of Asphalt
• Water-Permeable Materials
• Allow water to filter into the ground
• Keeps Pavement cool when moist
• Help control runoff and urban watershed
• Tokyo Study wet pavement 8C reduction in
  pavement temps.

Image from http//www.gaiaengineering.net/images/
photographs/porous_pavement/PorousPavement.JPG
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Albedos and Temperature
Image from http//heatisland.lbl.gov/Pavements/Lo
werTemps/
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EPA Cleaner Air

• EPAs 1990 Clean Air Act (CAA)
• Reduction of Toxic Air Pollutants
• Reducing Emissions of Greenhouse Gasses
• Phasing out Stratospheric Ozone-destroying
  chemicals (i.e. CFCs)
• Mandates that each state implement a plan and
  follow it to ensure cleaner air
• EPA also established the Air Quality Index (AQI)

Image from http//hvo.wr.usgs.gov/volcanowatch/20
05/images/ozone-pollution-smog.jpg
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Benefits of Cleaner Air

• Better for Human Health and Plant Health
• Indirectly reduces the effects of the UHI by
  decreasing the concentration of GH gasses and
  their warming effect

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Other UHI Mitigation Measures

• Better Building Materials
• Using lighter colored and highly emissive
  materials for walls
• Better City Planning
• Increasing Sky View
• More long wide buildings as opposed to tall
  skinny ones
• Planting Vegetation on side walls (see photo)
• Proper Building Ventilation
• Reworking Urban Watershed
• Turning off Air Conditioners

Image from http//en.wikipedia.org/wiki/ImageGre
en_City.jpg
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Current UHI Mitigation Projects

• EPA has taken the lead with the Heat Island
  Reduction Initiative (HIRI)
• Urban Heat Island Pilot Project (UHIPP)
• Began in 1998 in
• Baton Rouge
• Chicago
• Houston
• Sacramento
• Salt Lake City

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Current UHI Mitigation Projects

• Tree Canopy Programs
• Washington DC
• Sacramento
• Chesapeake Bay
• Benefits
• Improved Water Quality
• Decreased Energy Needs
• More Shade
• More Evapotranspiration
• Improved Air Quality

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Current UHI Mitigation Projects

• Green / Cool Roof Programs
• Portland
• Green Roof Activities
• Arizona
• Government buildings must reduce energy
• Reduced by 10 by 2008, and by 15 by 2010
• Austin, Texas
• Incentive Program
• 10 cent rebate per sq. meter of 75 reflective
  roof
• Cool Colors Project
• Aesthetically Pleasing Cool Roofs
• Mitigation Impact Screening Tool (MIST)
• Internet-based tool for city planners

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Benefits of UHI?

• Wintertime warming may
• Lower heating needs and thus energy costs
• Less snow and ice on roads less salting
• Harmful effects of outweigh helpful ones
• Most mitigation strategies can reduce summer UHI
  effects without eliminating winter benefits

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Conclusion

• What do we take out of all this?
• UHI is a problem, but there are measures that can
  reduce its effect
• Much research is done, many plans proposed, far
  fewer are actually implemented
• Must be practical and economically viable
• Takes a widespread collaborative effort
• Governments
• Businesses
• Individuals

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THE END

• Any Questions?