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AQA A-Level Human Geography > 🌆3.2.3.4 - Urban Climate > Flashcards

🌆3.2.3.4 - Urban Climate Flashcards

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1
Q

What aspects of the climate can urban areas modify?

A

Wind speeds
Temperature
Clouds and precipitation
Pollution

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2
Q

In what ways can winds be modified by urban areas?

A

Lower speeds
Greater variability
Large-scale convection

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3
Q

Why are wind speeds generally lower in urban areas?

A

The roughness of the land surface, consisting of buildings at a variety of heights, creates greater surface friction

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4
Q

What is an urban canyon?

A

A street with tall buildings either side but a space in between

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5
Q

What is the Venturi effect?

A

The effect of ‘squeezing’ the airflow, increased as buildings get taller towards the city centre

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6
Q

Where is the highest air pressure?

A

In the upper part of the building with air flowing down the front and over the top

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7
Q

How does convection occur over urban areas?

A

Convection and uplift over the area means that air pressure is lowered and air is drawn in from surrounding rural areas

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8
Q

What is the urban heat island?

A

Urban areas are on average 1-2 degrees warmer than their surrounding rural areas

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9
Q

What is albedo?

A

The degree of warming of a surface depends on the amount of insolation absorbed by the surface, which in turn depends on how much is reflected. The reflection is albedo.

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10
Q

What is sky view factor?

A

The amount of sky you can see without your view being impeded by tall buildings

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11
Q

What is specific heat capacity?

A

The amount of energy required to raise the temperature of 1kg of a material by 1 Kelvin

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12
Q

What is the intensity of an urban heat island?

A

The maximum difference between the temperature of the rural area and the peak urban temperature

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13
Q

How can weather conditions impact the intensity of the urban heat island?

A

High pressure systems with clear nights and sunny days increase the intensity

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14
Q

What are the five main factors causing urban heat islands?

A 
Anthropogenic heat
Height and arrangement of buildings
Nature of building materials
Presence of water
Pollutants
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15
Q

What is sensible heat?

A

Heat energy which can be felt, as opposed to latent heat which must be measured

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16
Q

How does cloud cover differ in urban areas?

A

It is greater

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17
Q

Why is cloud cover greater in urban areas?

A

There are more condensation nuclei, so cloud formation is greater

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18
Q

Why are there more thunder storms in cities?

A

Enhanced convectional uplift from the heat island can lead to instability in thermals, creating more storms

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19
Q

How do precipitation levels differ in urban areas?

A

They are higher

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20
Q

What is the speed effect?

A

Wind is slowed by friction from the building, friction with obstacles

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21
Q

What is the downdraught effect?

A

Turbulence is created around the top of the building, downdraught forms at the front

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22
Q

What is a downwind eddy?

A

A circular motion of wind behind the building and turbulence near the top of the building occurs as the wind is forced upwards

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23
Q

What can photochemical pollution lead to?

A

Smog - consisiting of ozone and peroxyacetyl nitrate (PAN)

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24
Q

When were London’s ‘Pea Soupers’?

A

December 1952

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25
Q

How did the smog form in London?

A

Windless, cold climate and an anticyclone (little wind, high pressure, still air) nothing moved and the particulates were trapped

26
Q

What did the smog cause?

A

Pneumonia, TB, heart failure, bronchitis

27
Q

How many died in the London smog?

A

4000+

28
Q

When was the clean air act introduced?

A

1956

29
Q

What is urban greening?

A

Involves growing plants wherever possible in urban areas

30
Q

What are the benefits of urban greening?

A

Improved air cooling, making towns and cities more bearable
Improving air quality by absorbing gases such as CO2
Improved respiratory health

31
Q

What is zoning of industry?

A

The process of dividing land into zones, and moving industry to the outskirts

32
Q

What does zoning of industry lead to?

A

Less particulates being trapped over the city in the cool, moist air above

33
Q

What are transport solutions?

A

Bus only lanes introduced to encourage the use of public transport in cities, congestion charges introduced

34
Q

How does temperature vary in cities?

A

Pockets of cool air above parks and water bodies (temperature sinks)
Highest temperature in industrial areas and densely populated areas

35
Q

Causes of Urban Island Effect

A

Absorption of heat by urban surfaces
Air pollution
Heat from human activity
Less evapotranspiration

36
Q

Absorption of heat by urban surfaces

A

. Urban surfaces have low albedoes- absorb heat in day, release it at night
. Windows reflect heat

37
Q

Air pollution

A

. Increased cloud cover
. ‘Pollution dome’
. Reflect outgoing heat into the city

38
Q

Heat from human activity

A

Air conditioning
Central heating
Cars

39
Q

Less evapotranspiration

A

. Little vegetation- less heat energy used, increased temp
. Water quickly removed through drainage systems, less to evaporate

40
Q

Issues with urban heat island effect

A

. Heat stroke
. Pressure on energy supplies (air con)
. Increased water consumption in warmer weather
. Increased evapotranspiration rates
. Plants flower longer + earlier (discomfort for allergy sufferers)
. Increases rates of temperature related chemical weathering

41
Q

Strategies to reduce urban heat island effect

A

Green roofs
Urban greening
Light cars
Discourage urban canyons

42
Q

How do green roofs reduce urban heat island effect?

A

Decreased roof temp 20-40C
Increased urban biodiversity

43
Q

How does urban greening reduce urban heat island effect?

A

Shade = cooling

44
Q

How do light cars reduce urban heat island effect?

A

Reflect heat
Cooler inside of car
Less air con needed

45
Q

How does discouraging urban canyons reduce urban heat island effect?

A

. Urban canyons decrease ventilation if perpendicular to prevailing winds
. Slows removal of heat

46
Q

Why are wind speeds overall slower in urban areas?

A

Tall buildings = friction

47
Q

Venturi effect

A

. Air squeezed between streets of tall buildings
. Creates high velocity winds

48
Q

How does urban heat island effect worsen urban winds?

A

. Urban heat island effect greatest at night
. Air drawn in from cooler surrounding areas
. Creates strong, localised win

49
Q

How can urban wind be reduced?

A

Buildings on stilts
Decreases pressure difference

50
Q

Causes of increased rain, fog, and thunderstorms in urban areas?

A

. Pollutants- condensation nuclei
. Urban heat island

51
Q

How does urban heat island worsen urban rain, fog, and thunderstorms?

A

. Warm moist air holds more water
. Rises (conventional uplift)
. Condenses, rain (conventional rain)

52
Q

Why is there less snow and frost in urban areas?

A

. Increased temperatures
. Melts quickly

53
Q

Causes of particulate pollution

A

. Vehicle exhausts (80%)
. Burning (cigarettes and refuse)
. Construction, mining, quarrying (cement dust)
. Plants, moulds (pollen, mould spores)

54
Q

Causes of photochemical pollution

A

Burning fossil fuels

55
Q

How can air pollution be reduced?

A

Transport
Clean Air Acts
Industrial Zoning
Urban Greening

56
Q

Ways to reduce air pollution: transport

A

Congestion charges
Pedestrianisation
Public transport
Alternative fuels

57
Q

When was the Clean Air Act introduced in London?

A

1956

58
Q

Ways to reduce air pollution: industrial zoning

A

. Too late in HIC’s
. LIC cities designed to have industry downwind
. Taller chimneys
. Force factories to reduce gas and particulate emissions (filters)

59
Q

Ways to reduce air pollution: Urban Greening

A

. Plants filter pollutants from air
. Plants in urban canyons- decreased NO2 by 40% and particulate matter by 60%

60
Q

Walkie Talkie

A

. Its curved face is channeling gusts strong enough to knock people over
. Reflects light intense enough to melt cars
. This is the downdraught effect when wind is forced downwards - most forceful when facing prevailing wind
. To solve problem protective fins have been added

AQA A-Level Human Geography (58 decks)

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