Urban Heat Islands

isnap.nd.edu

Urban Heat Islands

Zac Suriano


• What are Urban Heat Islands

• Their effects

• Prevention and accounting for changes


• A localized increase in temperatures found in major

urban areas (compared to rural surroundings)

Rural

Urban


• Two types of Islands; Surface and Atmospheric


Urban heat island is highest on calm, cloudless

summer nights


• Decrease in vegetation

• Trees and vegetation provide shade, which helps

lower surface temperatures. They also help reduce

air temperatures through a process called

evapotranspiration, in which plants release water to

the surrounding air, dissipating ambient heat.


Urban building materials

• They have low albedo and high emissivity meaning

more absorption and more radiating heat


Urban Geometry

• Basically with

high buildings

everywhere it

increases surface

area to absorb

heat and prevents

it from leaving

due to obstructions


• Anthropogenic heat

Heat created by human activities including

industrial processes, appliances etc

• Location and Weather

• Wind, cloud-cover, large bodies of water and higher

elevation all yield cooler temperatures

~160*F

~85*F

• Salt Lake City


• Increased Energy Consumption

• Research shows that electricity demand for cooling

increases 1.5–2.0% for every 1°F increase in air

temperatures, starting from around 70°F


• Increase in pollution and greenhouse gases due

to this increase in power needs

• Health risks include respiratory difficulties,

both non-fatal heat stroke, and heat-related

mortality, along with heat cramps and

exhaustion

• Can also intensify heat waves increasing problems


• A decrease in water quality is a result of runoff

water being heated from high road and roof

temperatures

• Can increase temperature

from 70 – 90 *F

• Very hazardous to aquatic life


• Increase vegetation

removes GHG emissions,

reduces runoff and help

prevent pavement

deterioration via shade

• Green Roofs putting

plants on roofs acts as

insulation to buildings

• Cool Roofs and

Pavement made of

material with high

albedo that enhance

water evaporation


• Shows unnatural increases in temperatures

measured in urban locations

• So if temperature observations are used in

assessment of global warming they would result in

an over-estimate!

???


• Turns out that according to a study by

Trenberth et al., it accounts for only

~0.006 *C/decade since 1900

• Only 8% of 0.74*C global warming (1906-2005)

• Started to be accounted for by adding error bars to

previous data

• Removal of UHI data sites

• Using location rural areas outside of cities


• According to the UN, in 2008 around 50% of

worlds population lived in Urban centers

• Increase in problems

• However:

• Counteractive strategies are becoming more popular

as roughly 8.5 million square feet of Green roofs

were installed in the United States as of June 2008


Akbari, H. 2005. Energy Saving Potentials and Air Quality Benefits of Urban

Heat Island Mitigation (PDF) (19 pp, 251K). Lawrence Berkeley

National Laboratory.

Arnfield, John et al. 2003. Two decades of Urban Climate research.

International Journal of Climatology. 23: 1-26

Heat Island Effect. United States EPA. Update: 3/29/11.

http://www.epa.gov/heatisld/

IPPC. Scientific Assessment of Climate change-Report of Working Group 1.

Cambridge University Press; 1990 ,365 pp.

Johnson, G. et al. 1991. Simulation of surface urban heat islands under ideal

conditions part 1. Boundary –Layer Meteorology. 56:3 275-294

Parker, David. 2010. Urban heat island effect on estimates of observed climate

change. WIREs Climate Change 2010. 1: 123-133

Reducing Urban Heat Islands: Compendium of Strategies. United States EPA.

http://www.epa.gov/heatisld/resources/pdf/BasicsCompendium.pdf

Trenberth KE, et al. Observations: surface and atmospheric climate change.

Climate Change 2007: The Physical Science Basis. Cambridge

University Press 2007, 235-336

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