Urban Climates

Question 1

Temperature

Answer 1

City temperatures 1 to 7 C higher

Question 2

Insolation

Answer 2

15 to 30% less insolation in cities
Due to more pollution and cloud which blocks insolation

Question 3

Cloud cover

Answer 3

5 and 10% more clouds in cities
More pollution and warm, unstable air

Question 4

Relative humidity

Answer 4

2 to 6% lower in cities:
Less evaporation (surfaces), transpiration (fewer plants)
Surface water removed quickly by drainage system
Warmer air (greater capacity to hold water vapour)

Question 5

Dust

Answer 5

10x more dust particles in city:
Traffic, construction, industry add dust and smoke to air.

Question 6

Fog and precipitation

Answer 6

More pollution and warmer air therefore:

More cloud, 5-10% more rain and more dew, frost and fog.

Question 7

Wind

Answer 7

Cities develop their own circulation patterns because buildings affect the flow of air
Can act as wind breaks(friction - slower wind speed)
Channel wind, causing strong, gusting wind (more turbulence)

Question 8

Urban heat islands

Answer 8

The part of the city (CBD) where temperatures are consistently higher than the surrounding and rural areas

Question 9

Reasons for higher temperatures in cities

Answer 9

Production of artificial heat (cars, heating systems, air conditioners, factories, restaurants)

Types of artificial surfaces (absorb and retain heat and reradiate it at night e.g. tar, concrete, steel. Reflect heat e.g. glass)

Tall buildings trap heat (large surface area that can absorb and retain heat and reradiate it at night)

Lots of pollution due to industry, construction, motor vehicles (results in more cloud which traps heat and there are more pollutants to absorb heat (greenhouse effect)

Less vegetation (less heat lost through photosynthesis, transpiration etc.)

Less surface water due to drains, gutters etc, so less heat is used for evaporation

Question 10

Negative effects of urban heat islands

Answer 10

Increased human discomfort.
Heat stress and deaths during heat waves.
Increased conditions for spread of vector borne disease
Reduced visibility due to smog, particularly in winter
Increased energy usage
Increased costs due to greater energy and water usage

Question 11

Pollution dome

Answer 11

Concentration of polluted air in and above a city at night, caused by an inversion above it

Question 12

Pollution dome night

Answer 12

Cooler air as fewer hear courses are on at night (more stable air in lower atmosphere)

Pollution is trapped below the inversion layer.

Pollutants are concentrated over the city and cannot escape, so a pollution dome is formed

Is there is a wind, a pollution plume may form downwind.

Question 13

Pollution dome day

Answer 13

Warmer, more heat
Causes unstable, rising air and fertile increase in the heat island.

Pollution is spread over a larger area and is not as concentrated

Greater turbulence means pollutants are dispersed

Question 14

Effects of the pollution dome

Answer 14

Lead to poisoning from petrol fumes and peeling point.

Respiratory problems and asthma attacks from smoke.

More cloud cover and precipitation

Less insolation

Causes smog reducing visibility and is harmful.

Acid rain damages buildings and pollutes rivers and lakes causing plants and fish to die.

Contributes to global climate change.

Question 15

Strategies to reduce heat island effect

Answer 15

Energy saving measures e.g. solar power, improved public transport

Creating urban green spaces e.g. parks rooftop and verticals gardens

Appropriate building design e.g. materials, lighter colours