Urban areas experience unique microclimates caused by human activities and infrastructure. The document discusses four main types of urban stress: poor housing, congestion, environmental problems, and social issues. It provides examples of each from around the world, such as slums in Manila, rush hour traffic in Los Angeles, pollution in Beijing, and crime in Caracas. Tall buildings in cities disrupt wind patterns, create heat islands with higher temperatures, and change rainfall and humidity compared to rural areas.

1. URBAN MICROCLIMATES: TEMPERATURES
Temperatures in Atlanta, GA
(vegetation vs built areas)
Urban “heat islands” : average difference between CBD and countryside =
+0.6oC (morning) and +3o/4oC (evening)
Watch www.youtube.com/watch?v=t-sXHl3l-rM
© 2011 Antoine Delaitre 1

2. Low albedo of many urban building materials + lack of evapotranspiration higher evening temperatures
© 2011 Antoine Delaitre 2

3. UBL (Urban Boundary Layer)
= warm/polluted layer
of air above city
UCL (Urban Canopy Layer)
= warm layer of air
near ground
© 2011 Antoine Delaitre 3

4. URBAN MICROCLIMATES: WIND + CONDENSATION
Tall constructions disrupt air flow and reduce wind speed/evaporation (except “canyon effect”)
Urban “canyon effect”
© 2011 Antoine Delaitre
Urban pollution particles + heat convection + condensation + rain 4

5. URBAN MICROCLIMATES
CHARACTERISTICS OF URBAN
CAUSES AND EFFECTS
MICROCLIMATE
Watch www.youtube.com/watch?v=t-sXHl3l-rM
•Tall buildings less wind
•Pollution of fossil fuels (cars+factories) + central heating + humans heat +
particles smog which traps outgoing radiant energy (greenhouse effect)
“HEAT ISLAND” OVER CBD
•Low albedo of most building materials (asphalt, concrete, metal) reflects
(HIGHER TEMPERATURE) less solar radiation (=absorb heat during day and release it at night)
•Average temperature difference between CBD and countryside = +0.6oC
(morning) and +3o/+4oC (evening) less frost/snow, early blooming, more
A/C.
more dust particles and fumes + higher buildings less sunlight radiation (in
LESS SUNLIGHT spite of higher temperatures) with considerable local contrasts however (CBD
= very shaded)
•Tall buildings act as windbreaks wind velocity 30% lower than in
LESS WIND countryside
(EXCEPT “CANYON EFFECT”) •Sometimes, high-rises can also form “canyons” which channel air and create
strong local winds and turbulences (NY, Hong Kong)
DRYER AIR Higher temperature + lack of vegetation = air 6% dryer than in countryside
Higher temperature + wind convection + more particles to condensate
MORE CLOUDS/FOG/RAIN
moisture thicker and more frequent clouds/fogs over cities (5-15% more
(“URBAN PLUME”) rain, 25% more thunder, 400% more hail)
© 2011 Antoine Delaitre 5

6. URBAN STRESS #1: POOR HOUSING
Slum in Manila (Philippines) Port-au-Prince (Haiti)
Apartment complexes in Hong Kong (China)
© 2011 Antoine Delaitre 6

7. URBAN STRESS #2: CONGESTION
Rush hour in Los Angeles “Go-Slow” in Lagos (Nigeria)
Rapid transit (“RER”) in greater Paris area Streets in the center of London (UK)
© 2011 Antoine Delaitre 7

8. URBAN STRESS #3: ENVIRONMENTAL PROBLEMS (“Brown Agenda”)
An “outhouse” in Bangladesh São Paulo (Brazil)
Beijing (China) Riverbanks of the Nile (Sudan)
© 2011 Antoine Delaitre 8

9. URBAN STRESS #4: SOCIAL PROBLEMS
Caracas (Venezuela)
Family in India Belfast, Northern Ireland (UK)
© 2011 Antoine Delaitre 9

10. Types of
ENVIRONMENTAL AND URBAN STRESS
urban stress
Poor housing can be a major problem (LEDC):
•Quality: water, sanitation, electricity, square footage per person, reliable construction (antiseismic, etc)
Poor housing •Quantity: supply/demand (e.g. Hong Kong)
•Affordability: slums vs affluent neighborhoods (e.g. Lima)
•Security of tenure: ownership vs rental vs squatting (Mexico City)
MEDCs: LEDCs:
•Reliance on private cars rather than public •Lack of urban planning, street organization and strict
transportation + competition for street space between traffic regulations congestion (e.g. “go-slows” in
traffic, parking, bike lanes, pedestrian zones, Lagos)
roadwork congestion (Los Angeles, London) •No traffic flow control (Lima, Bangkok)
Congestion •Lack of efficient traffic flow control (Los Angeles) •Many vehicles in poor condition air + noise
•Abundance of cars air + noise pollution pollution
•Urban sprawl + public transportation to/from CBD •Urban growth > growth of transportation network
but not adapted to inter-suburb transit between very long commute
suburban edge cities long commute (SF Bay, Paris) •Lack of public funding unregulated + dysfunctional
•Medieval streets not adapted to traffic (London) transportation network (e.g. Ouagadougou, Lagos)
“Brown Agenda” = range of environmental problems in LEDC:
Environmental •Problems linked to lack of land (Rio), water (Mexico City), green spaces (Sao Paulo) and public services (lack of
problems trash collection in Cairo or Dhaka)
•Problems linked to pollution: water, air (China), soil, toxic waste (e.g. 1984 industrial pollution in Bhopal, India:
“Brown Agenda” 4,000+ deaths)
Some common social problems in Third World cities include:
•Difficult access to services for underclass (e.g. education, health, banking)
Inequalities and •Ethnic/religious discrimination socio-eco polarization (Belfast, Jerusalem, Johannesburg)
social problems •Poverty + limited police presence Crime (e.g. Caracas)
© 2011 Antoine Delaitre 10