Urbanization refers to the increasing concentration of population in cities and the transformation of land use to an urban pattern. It is driven by economic factors as people migrate from rural to urban areas for work opportunities. While urbanization brings economic benefits, it also concentrates environmental impacts like pollution, resource use, and waste generation. To develop more sustainably, cities must improve existing infrastructure and plan future development to minimize environmental footprints while meeting growth needs through compact design and alternative transportation options. Understanding urban systems as complex interacting processes is key to managing urbanization's impacts at local and global scales.

2. What is urbanization?
 The migration of people from rural areas and villages
into high-population-density “cities”, and the
associated growth of these cities and the
transformation of their physical, social and economic
environment (Elie’s)
 Another definition is thus: “An increasing concentration
of the population in cities and a transformation of land
use to an urban pattern of organization.”

3. • Urbanization is a global
trend, but it is fastest
in developing countries
which still have a low
urban population
percentage
• It is ongoing: more
cities are created and
megacities (like
Moscow) can grow
even bigger

4. Degrees of urbanization
Rural
Ex-urban Suburban
Urban
urban sprawl:
spatial expansion of cities

5. When and why did humanity start
urbanizing?
 http://en.wikipedia.org/wiki/List_of_cities_by_time_of_continuous
_habitation
 Homo sapiens have existed on earth for about 200,000 years, but
cities have existed for less than 10,000 years.
 A long time ago: ~5000 BC large permanent settlements started
appearing around the Mediterranean. Cities needed developed
agriculture to produce surplus food outside of cities for them.
 Maybe because we found cities to be more stable, prosperous and
safe (back when cities were better defended against invaders)
 … in any case the, the main motivations for people to move to
urban areas today are economic, and the incentives remain very
strong
 Thus urbanization will continue

6. Chicago in 1820: population 15

7. Chicago in 1898: population 1.6 million

8. Chicago+ in 2012: population 9.5 million

9. Where are we today?
More at:
http://www.un.org/esa/population/publications/wup20
07/2007WUP_Highlights_web.pdf

10. Where are we today?
http://esa.un.org/unpd/wup/maps_1_2009.htm

11. Urbanization and per capita GDP: e.g. China
http://www.mckinsey.com/mgi/reports/pdfs/c
hina_urban_billion/China_urban_billion_full_r
eport.pdf
Urban population > 50% ~ 2014
The Economist

12. So where does this leave us?
 Urbanization will continue and eventually, at
some point, most countries will have urbanization
rates > 80%
 Thus the question is How to Urbanize? And
1. preserve the environmental quality in cities
2. avoid significant regional and global impacts of
urban areas
This is where a combination of
policy, science, engineering is needed

13. How does it affect the environment?
 Changes the surface to solid, impervious material
with different thermal properties
 Changes the topology of the surfaces from low
roughness vegetation or porous forests to
complex bluff bodies (buildings)
 Reduces natural water vapor release to the
atmosphere (surfaces do not hold water), but
 Increases the anthropogenic production of heat
and water vapor
 Increases the emissions of air pollutants and
greenhouse gases

14. So is it “bad”?
Not necessarily:
1. Buildings, with small apartments and shared walls, need less
energy to heat and cool than big houses.
2. Compact cities reduce commuting and transportation
impacts (but create traffic jams that can take back some of
these advantages), are more amenable to public
transportation solutions (but food and other things might
have to be transported from far away)
 So on average, city residents pollute less and emit less GHG,
 http://eau.sagepub.com/content/early/2011/01/08/095624781039
2270
 http://siteresources.worldbank.org/INTUWM/Resources/GHG_Inde
x_Mar_9_2011.pdf

15. Per capita, city residents emit less GHGs
Thanks Liuye
5.5 2005
…except in developing countries
where the urban population is
much richer than rural populations
http://eau.sagepub.com/content/early/2011/01/08/0956247810392270

16. But it is concentrated
 Higher density means all of these impacts are concentrated
rather than diluted.
 Urban environmental problems are very local: cities cover ~
3-4% of the earth’s land surface
(http://www.livescience.com/6893-cities-cover-earth-
realized.html)
 Cities can have an impact on regional climate and
environment, especially if large or concentrated (10% of
coastal areas are urbanized  coastal cities)
 Cities can have serious impacts on water quality in adjacent
water bodies and need very large waste landfills
 Unlikely to have a major direct impact on global climate!
…yet

17. Environmental Footprint of Cities 1
 An environmental footprint, of a product, city, or process, is the equivalent
land surface needed to sustainably produce the material, food, and other
items needed to make the product, sustain the city’s activity, or perform
the process. (Read “Our ecological Footprint: Reducing Human Impact on
the Earth” by Wackernagel and Rees)
 London has an area of 170,000 ha but an environmental footprint of
21,000,000 ha.
 On average, slum dwellers in New Delhi, India, require only 0.8 hectares of
land per capita to maintain their minimal lifestyles, while Americans in
Boston or New York need 8.4 hectares of land per capita to support their
consumption levels.
http://ww2.unhabitat.org/cdrom/wuf/documents/Dialogues/Added%20m
aterial%20during%20WUF%20II/Urban%20Sustainability/Presentation%20
by%20Mr.%20Bakary%20Kante.pdf

18. Environmental Footprint of Cities 2
 Another possible use of “environmental footprint of a
city” is to indicate the surrounding area where the
impacts of the city are directly felt, maybe in terms of air
quality, hydrometeorological parameters, or other
environmental variables.
Areas in red depict the dimensions
of the main aerosol mass
emanating from Beijing during the
opening weekend of the Summer
Olympics. Models predict cleaner
skies in the starting days of the
Games. Image: Greg
Carmichael/University of Iowa.

19. So the question is
How to Urbanize more
sustainably?
 Improve the functioning of existing cities
 Building better future cities
 But cities are complex and we need to
understand individual processes, how they
interact, and how they function together in
the “urban system”

20. Large
Picture:
Urban
Systems
Modeling
Each
subprocess
is complex
Processes
Interact &
compete
http://www.cdm.com/en-
us/Insights/Neysadurai-Centre/Urban-Systems-