An explanation of why urban areas are warmer than the surrounding rural areas. Runoff, pollution, heat, pavement, roads, sediment ponds

1. How Can Urbanization Affect
a Local Area?
What we build and how to live with it
By Kella Randolphn B.S., M.Ed.

2. • Urban Heat Islands
• http://www.usatoday.com/story/weather/2014/08/21/urban-heat-islands-study/14389371/

3. What is the Urban
Heat Island Effect?
An urban heat island (UHI) is a metropolitan
area which is significantly warmer than its
surrounding rural areas. The phenomenon
was first investigated and described by Luke
Howard in the 1810s. The temperature
difference usually is larger at night than
during the day, and is most apparent when
winds are weak.

4. Concrete gets hotter
than grass.
The main cause of the
urban heat island is
modification of the land
surface by urban
development which uses
materials which
effectively retain heat.
http://ramconroofing.blogspot.com/2013/11/what-is-
urban-heat-island-effect.html

5. Heat from cars and
indoor heating systems
add to the problem.
Waste heat generated by
energy usage is a secondary
contributor. As population
centers grow they tend to
modify a greater and greater
area of land and have a
corresponding increase in
average temperature.
http://ramconroofing.blogspot.com/2013/11
/what-is-urban-heat-island-effect.html

6. Cities change
surrounding
ecosystems.
Monthly rainfall is greater
downwind of cities, partially due to
the UHI. Increases in heat within
urban centers increases the length
of growing seasons, and decreases
the occurrence of weak tornadoes.
The UHI decreases air quality by
increasing the production of
pollutants such as ozone, and
decreases water quality as warmer
waters flow into area streams,
which stresses their ecosystems.
http://ramconroofing.blogspot.com/2013/11
/what-is-urban-heat-island-effect.html

7. How to make it better
Mitigation of the urban heat
island effect can be
accomplished through the
use of green roofs and the
use of lighter-colored
surfaces in urban areas,
which reflect more sunlight
and absorb less heat.
http://ramconroofing.blogspot.com/2013/11/what-is-
urban-heat-island-effect.html

8. Green areas and lighter colored buildings are cooler.

9. Cities hold the heat longer into the night.

10. About 80% of people live in or near cities.
For the first time in human history, more
people live in cities than rural environments
and this trend is likely to increase.
City regions can typically have air temperatures
warmer than surrounding rural environments
by anywhere from 1 to 15 degrees F.
Atlanta thermal image at night showing the surface urban heat island. Courtesy of
NASA.
http://www.forbes.com/sites/marshallshepherd/2015/09/25/the-science-of-why-cities-
are-warmer-than-rural-areas/#778e8e9b745b

11. More heat related illnesses
• Heat islands can lead to
increases in heat related health
issues and mortality, increased
energy demand, higher air
conditioning costs, and more air
pollutions and greenhouse gas
emissions.
Less evapotranspiration
• Cities also tend to have less
trees and vegetation within the
central business district or city
center. Less vegetation means
less evapotranspiration. Like
evaporation of perspiration from
our skin, evapotranspiration is a
cooling process.

12. The combination of heat-absorbing surfaces, lack of evapotranspirational
cooling, and waste heat causes the Urban Heat Island.
http://www.forbes.com/sites/marshallshepherd/2015/09/25/the-science-of-why-cities-are-warmer-than-rural-areas/#778e8e9b745b

13. Based on data from 2004-13, the top 10 U.S. cities with the most intense urban heat
islands -- measured as the greatest difference in average temperatures between
urban and rural areas over the entire summer -- were:
Cities also tend to have many more extremely hot days each year, on
average, than nearby rural areas, the report found. Over the past 10
years, cities had an average of at least eight more days over 90 degrees
each summer, compared to nearby rural areas Our hottest urban heat islands
• Las Vegas (7.3°F)
• Albuquerque (5.9°F)
• Denver (4.9°F)
• Portland (4.8°F)
• Louisville (4.8°F)
• Washington, D.C. (4.7°F)
• Kansas City (4.6°F)
• Columbus (4.4°F)
• Minneapolis (4.3°F)
• Seattle (4.1°F)
http://www.usatoday.com/story/weather/2014/08/21/urban-
heat-islands-study/14389371/

14. Las Vegas, Albuquerque and Denver lead the list of U.S. cities with the
most intense urban heat islands, according to a report released this
week by research organization Climate Central, which is based in
Princeton, N.J.
"Urban heat islands have hotter days, far hotter nights, and more
extremely hot days each summer than adjacent rural areas," said
Alyson Kenward, lead author of the report and senior scientist with
Climate Central.
The concrete, asphalt and shingled roofs of buildings, roads and other
infrastructure in urban environments usually make cities much hotter
than surrounding rural
areas.http://www.usatoday.com/story/weather/2014/08/21/urban-heat-islands-
study/14389371/

15. http://usatoday30.usatoday.com/weather/wurbheat.htm

16. Urban Flooding
http://www.floodsite.net/juniorfloodsite/html/en/student/thingstoknow/hydrology/urbanfloods
.html
Urban flooding is specific in the fact that the
cause is a lack of drainage in an urban area.
As there is little open soil that can be used
for water storage nearly all the precipitation
needs to be transport to surface water or
the sewage system. High intensity rainfall
can cause flooding when the city sewage
system and draining canals do not have the
necessary capacity to drain away the
amounts of rain that are falling. Water may
even enter the sewage system in one place
and then get deposited somewhere else in
the city on the streets.

17. Surface Water Runoff
When rain or snow falls onto the earth, it just
doesn't sit there, it starts moving according
to the laws of gravity. A portion of the
precipitation seeps into the ground to
replenish Earth's groundwater. Most of it
flows downhill as runoff. Runoff is extremely
important in that not only does it keep rivers
and lakes full of water, but it also changes the
landscape by the action of erosion. Flowing
water has tremendous power—it can move
boulders and carve out canyons; check out
the Grand Canyon!
Runoff of course occurs during storms, and
much more water flows in rivers (and as
runoff) during storms. For example, in 2001
during a major storm at Peachtree Creek in
Atlanta, Georgia, the amount of water that
flowed in the river in one day was 7 percent
of all the streamflow for the year.
U.S. Department of the Interior | U.S.
Geological Survey URL:
http://water.usgs.gov/edu/gallery/imperviou
s-areas-air.html

18. Sediment Ponds
Many cities and shopping centers
build a basin to catch runoff from
rains and sudden storms. Water
cannot seep into the ground
through paved streets, roads and
parking lots. So a pond is created to
catch and hold the water until some
of it can evaporate while most of
the runoff can seep into the
ground. This prevents flooding
downhill from the paved areas.
http://water.usgs.gov/edu/mearthsw.html