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A Level Human Geography > Urban Climate > Flashcards

Urban Climate Flashcards

1
Q

Define urban heat island effect

A

The temperature difference between urban / suburban areas and the surrounding rural areas

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2
Q

What is the average temperature difference between an urban area and its surroundings?

A

1-3°C warmer in a city.

Clear, calm night -> 12°C warmer.

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3
Q

What are the factors that cause urban temperatures to vary?

A

Season
Weather conditions
Sun intensity
Ground cover

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4
Q

Give reasons for when UHI varies

A

Largest in summer

Decreases as size of city decreases

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5
Q

Give reasons why cities are warmer than rural areas

A
  • Less reflective surfaces -> much lower albedo, absorb heat during day, slowly release heat at night.
  • Air pollution from industry / vehicles -> increase cloud cover + ‘pollution domes’ absorb outgoing radiation.
  • Disposal of water runoff -> changes urban moisture / heat budget.
  • Heat emitted from industry / vehicles / buildings / people.
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6
Q

Why is UHI a concern?

A
  • Hot temps make indoors / transport uncomfortable.
  • Heat stroke, asthma, organ damage, deaths -> esp babies / elderly.
  • UHI caused by hot, still, anticyclonic weather conditions -> more air pollution.
  • Hot temps -> strain on energy for cooling / air con.
  • Strain on water resources -> higher human consumption (drinking), more evapotranspiration, plants extract more from soil.
  • Earlier flowering times / prolonged growing season -> allergies.
  • Higher reproduction / lifespan of animals, insect pests.
  • More algae in water.
  • More deterioration of historical monuments / buildings -> more temp-related chemical weathering.
  • Climate change -> increase intensity of UHI.
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7
Q

Name the policies for reducing pollution / managing UHI

A 
Cool surfaces.
Green roofs.
Urban greening.
Sky view factor.
Cool cars.
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8
Q

What are ‘cool surfaces’ as a policy to reduce pollution / manage UHI

A

Eg cool roofs, cool pavements

-> made of materials with high solar reflectance -> absorb / store less solar energy during day -> emit less at night

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9
Q

What are ‘green roofs’ as a policy for reducing pollution / managing UHI?

A

Eg Plants on rooftops

  • > lower roof temps by 20-40°C on a sunny day.
  • > reduce rainwater runoff.
  • > increase biodiversity.
  • > insulators.
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10
Q

What is ‘urban greening’ as a policy for reducing pollution / managing UHI?

A

Eg Planting trees / vegetation

  • > provides shade.
  • > reduce peak temps by 5-20°C.
  • > trees reduce urban flooding.
  • > trees filter pollutants.
  • > trees = Carbon store.
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11
Q

Define ‘sky view factor’

A

Relative openness between buildings

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12
Q

How does ‘sky view factor’ affect UHI?

A

Restricted sky view…

  • > reduce escape of heat from surfaces -> heat builds up in ‘street canyons’.
  • > reduce ventilation in UHIs if streets at 90° to prevailing winds.
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13
Q

What are ‘cool cars’ as a policy for reducing pollution / managing UHI?

A

Eg light colour car shells

  • > reflect more sunlight -> reduce need for air conditioning.
  • > cars are large contributors to UHI and pollution.
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14
Q

Which parts of local climate do urban areas affect?

A

Wind speed
Temperature
Clouds / precipitation
Pollution

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15
Q

What percentage of the world’s population is predicted to live in urban areas by 2025?

A

80%

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16
Q

How can urban areas affect wind?

A

Lower speeds
Greater variability
Large scale convection

17
Q

Do urban areas have lower wind speed than outlying suburbs? Why?

A

Average 5% lower wind speed in city centre.

-> roughness of land surface -> increase surface friction

18
Q

Why does wind speed vary in cities?

A

Due to layout of buildings / building height.

19
Q

Where do ‘urban canyons’ form? How?

A

Straight streets lined with tall buildings -> urban canyons.

Buildings funnel winds -> Venturi effect -> high velocity

20
Q

How is wind turbulence created?

A

High rise buildings disrupt the flow of air -> turbulence.

Any air not flowing in the general direction will cause turbulence

21
Q

Give an advantage and disadvantage of wind turbulence / gustiness

A

Adv - turbulence ‘flushes out’ pollutants at street level.

Dis - unpleasant for pedestrians

22
Q

What does ‘large scale convection’ caused by UHI lead to?

A

-> lowering air pressure -> air is drawn in from surrounding rural areas

23
Q

Define ‘intensity’ of UHI

A

The maximum difference between the temperature of the rural area and peak urban temperature -> at night

24
Q

Name the factors that influence the intensity of UHI

A
  • Weather conditions -> high pressure systems with clear nights, still sunny days -> increase intensity.
  • Season
25
Q

Name the main factors that create UHI

A
  • Anthropogenic heat
  • Height / arrangement of buildings
  • Nature of building materials
  • Presence of water
  • Pollutants
26
Q

Define anthropogenic heat

A

Heat released by human activity

Eg vehicles, central heating (/air conditioning), industry

27
Q

Give the reasons for rainfall patterns in urban areas

A
  • UHI creates convection : rapid evapotranspiration -> clouds.
  • High rise buildings / range of heights -> air turbulence + increased vertical motion.
  • Surface winds drawn in from surrounding areas due to low pressure / prevailing winds move over city -> friction from urban boundary acts similar to mountain barrier -> air travels downwind of high rise buildings -> converge and rise upward -> rain clouds.
  • City pollution -> pollutants are ‘water attracting’.
  • Industry / power stations -> release water vapour -> clouds.
28
Q

What percentage more rainfall is there downwind from major areas, compared to upwind?

A

20% more rainfall downwind from major areas

29
Q

Why is there more rainfall downwind from major areas than upwind?

A

Heating of the surface / overlying air -> instability in atmosphere -> encourages air to rise.
Cools as it rises -> water vapour condenses into rain -> falls downwind of the city.

30
Q

Why has the occurence of fog in urban areas increased?

A

Industrialisation

Eg London early 1700s - 20 days of fog per year
London late 1800s - over 50 days of fog per year

31
Q

Why is there more fog in urban areas than rural areas?

A

Greater average number of particles in the are in urban areas.
Particles act as condensation nuclei -> encourage fog formation at night under high pressure conditions.

32
Q

What strategies have been used to reduce the amount of fog in urban areas?

A

Clean Air Acts of 1950s

-> reduced smoke production, fewer particulate emissions in U.K. -> fewer foggy days

33
Q

Give examples of places that experience high levels of fog.

What is the issue associated with this?

A

New Delhi, Beijing -> regular winter fogs.

‘Airpocalypse’ - fog traps pollutants -> toxic smog -> high death toll.

35
Q

How is thunder created?

A

Extreme temperature -> rapid expansion of air -> shockwave -> thunder.

36
Q

What is a reason thought to explain why there are more thunderstorms in urban areas?

A

Air pollution -> disturbs electrical charge of clouds -> lightning

40
Q

How is lightning created?

A

By conventional heating and rapid uplift of air -> instability in atmosphere.
Uplifted air rapidly cools and condenses due to cold clouds -> releasing its heat -> further uplift.
Positive electrical charges build up in clouds -> lightning

A Level Human Geography (15 decks)

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