III. Urban stress

© 2011 Antoine Delaitre 1

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

Temperatures in Atlanta, GA(vegetation vs built areas)

URBAN MICROCLIMATES: TEMPERATURES


Low albedo of many urban building materials + lack of evapotranspiration higher evening temperatures


UBL (Urban Boundary Layer)= warm/polluted layer

of air above city

UCL (Urban Canopy Layer)= warm layer of air

near ground


Tall constructions disrupt air flow and reduce wind speed/evaporation (except “canyon effect”)

Urban pollution particles + heat convection + condensation + rain

Urban “canyon effect”

URBAN MICROCLIMATES: WIND + CONDENSATION


CHARACTERISTICS OF URBANMICROCLIMATE CAUSES AND EFFECTS

“HEAT ISLAND” OVER CBD(HIGHER TEMPERATURE)

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)•Low albedo of most building materials (asphalt, concrete, metal) reflects 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.

LESS SUNLIGHTmore dust particles and fumes + higher buildings less sunlight radiation (in spite of higher temperatures) with considerable local contrasts however (CBD = very shaded)

LESS WIND(EXCEPT “CANYON EFFECT”)

•Tall buildings act as windbreaks wind velocity 30% lower than in countryside•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

MORE CLOUDS/FOG/RAIN(“URBAN PLUME”)

Higher temperature + wind convection + more particles to condensate moisture thicker and more frequent clouds/fogs over cities (5-15% more rain, 25% more thunder, 400% more hail)

URBAN MICROCLIMATES


URBAN STRESS #1: POOR HOUSING

Slum in Manila (Philippines) Port-au-Prince (Haiti)

Apartment complexes in Hong Kong (China)


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)


URBAN STRESS #3: ENVIRONMENTAL PROBLEMS (“Brown Agenda”)

São Paulo (Brazil)

Beijing (China) Riverbanks of the Nile (Sudan)

An “outhouse” in Bangladesh


URBAN STRESS #4: SOCIAL PROBLEMS

Caracas (Venezuela)

Family in India Belfast, Northern Ireland (UK)


Types ofurban stress ENVIRONMENTAL AND URBAN STRESS

Poor housing

Poor housing can be a major problem (LEDC):•Quality: water, sanitation, electricity, square footage per person, reliable construction (antiseismic, etc)•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)

Congestion

MEDCs:•Reliance on private cars rather than public transportation + competition for street space between traffic, parking, bike lanes, pedestrian zones, roadwork congestion (Los Angeles, London)•Lack of efficient traffic flow control (Los Angeles)•Abundance of cars air + noise pollution•Urban sprawl + public transportation to/from CBD but not adapted to inter-suburb transit between suburban edge cities long commute (SF Bay, Paris)•Medieval streets not adapted to traffic (London)

LEDCs:•Lack of urban planning, street organization and strict traffic regulations congestion (e.g. “go-slows” in Lagos)•No traffic flow control (Lima, Bangkok)•Many vehicles in poor condition air + noise pollution•Urban growth > growth of transportation network very long commute•Lack of public funding unregulated + dysfunctional transportation network (e.g. Ouagadougou, Lagos)

Environmental problems

“Brown Agenda”

“Brown Agenda” = range of environmental problems in LEDC:•Problems linked to lack of land (Rio), water (Mexico City), green spaces (Sao Paulo) and public services (lack of trash collection in Cairo or Dhaka)•Problems linked to pollution: water, air (China), soil, toxic waste (e.g. 1984 industrial pollution in Bhopal, India: 4,000+ deaths)

Inequalities and social problems

Some common social problems in Third World cities include:•Difficult access to services for underclass (e.g. education, health, banking)•Ethnic/religious discrimination socio-eco polarization (Belfast, Jerusalem, Johannesburg)•Poverty + limited police presence Crime (e.g. Caracas)

III. Urban stress

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