Urban Climate

Question 1

How does temperature vary in cities?

Answer 1

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

Question 2

Causes of Urban Island Effect

Answer 2

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

Question 3

Absorption of heat by urban surfaces

Answer 3

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

Question 4

Air pollution

Answer 4

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

Question 5

Heat from human activity

Answer 5

Air conditioning
Central heating
Cars

Question 6

Less evapotranspiration

Answer 6

Little vegetation- less heat energy used, increased temp

Water quickly removed through drainage systems, less to evaporate

Question 7

Issues with urban heat island effect

Answer 7

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

Question 8

Strategies to reduce urban heat island effect

Answer 8

Green roofs
Urban greening
Light cars
Discourage urban canyons

Question 9

How do green roofs reduce urban heat island effect?

Answer 9

Decreased roof temp 20-40 oc

Increased urban biodiversity

Question 10

How does urban greening reduce urban heat island effect?

Answer 10

Shade = cooling

Question 11

How do light cars reduce urban heat island effect?

Answer 11

Reflect heat
Cooler inside of car
Less air con needed

Question 12

How does discouraging urban canyons reduce urban heat island effect?

Answer 12

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

Question 13

Why are wind speeds overall slower in urban areas?

Answer 13

Tall buildings = friction

Question 14

Venturi effect

Answer 14

Air squeezed between streets of tall buildings

Creates high velocity winds

Question 15

How does urban heat island effect worsen urban winds?

Answer 15

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

Question 16

How can urban wind be reduced?

Answer 16

Buildings on stilts

Decreases pressure difference

Question 17

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

Answer 17

Pollutants- condensation nuclei

Urban heat island

Question 18

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

Answer 18

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

Question 19

Why is there less snow and frost in urban areas?

Answer 19

Increased temperatures

Melts quickly

Question 20

Causes of particulate pollution

Answer 20

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

Question 21

Causes of photochemical pollution

Answer 21

Burning fossil fuels

Question 22

How does photochemical smog form?

Answer 22

Nitrogen oxide
Sulphur oxide
Meet sunlight, break down into harmful chemicals i.e. ozone
Temperature inversion, pollutants kept at ground level
(Respiratory illness and headaches)

Question 23

How can air pollution be reduced?

Answer 23

Transport
Clean Air Acts
Industrial Zoning
Urban Greening

Question 24

Ways to reduce air pollution: transport

Answer 24

Congestion charges
Pedestrianisation
Public transport
Alternative fuels

Question 25

When was the Clean Air Act introduced in London?

Answer 25

1956

Question 26

Ways to reduce air pollution: industrial zoning

Answer 26

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

Question 27

Ways to reduce air pollution: Urban Greening

Answer 27

Plants filter pollutants from air

Plants in urban canyons- decreased NO2 by 40% and particulate matter by 60%