Urban Heat Island

Question 1

Venturi effect

Answer 1

Wind funnelled into narrow urban canyons created by tall buildings, speeds up as it becomes more restricted

Question 2

UHI

Answer 2

An urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities.

Question 3

Albedo

Answer 3

A measure of how much light that hits a surface is reflected without being absorbed. Something that appears white reflects most of the light that hits it and has a high albedo, while something that looks dark absorbs most of the light that hits it, indicating a low albedo.

Question 4

Anthropogenic Heat

Answer 4

Heat given off through human activity, such as vehicles, central heating/air conditioning and industry. These add heat to the urban environment raising its temperature above the rural surroundings.

Question 5

Height/arrangement of buildings

Answer 5

The arrangement of tall buildings in close proximity is the main factor in generating the urban heat island. The urban albedo is much lower than the rural albedo (more heat absorbed). Vertical surfaces reflect the heat and as buildings are close together (lower sky-view factor) the radiated heat gets

Question 6

Building materials

Answer 6

Compared to rural areas, urban areas heat up more quickly. The specific heat capacity for concrete is one-third that of bare soil, and so for a given input of energy, concrete will warm up more quickly. With vertical buildings, surface area is increased in cities and so absorbs more heat. This gets released at night.

Question 7

Pollutants

Answer 7

These can have both a cooling/heating effect. Dust and smog can reduce sunlight by as much as 6% causing a cooling effect. CO2 absorbs long-wave radiation which heats the urban dome further.

Question 8

The presence of water

Answer 8

Radiated heat can be transferred as sensible or latent heat. Latent heat evaporates water, sensible heat is heat energy that can be felt. After evapotranspiration, any left over heat is used to warm the air. The more sensible heat that enters the atmosphere, the warmer it gets. As there is little water in urban areas, little latent heat is needed so becomes sensible heat further warming the air.

Question 9

Sky view factor

Answer 9

This is the amount of sky we can see without our view being impeded by tall buildings.

Question 10

Specific Heat Capacity

Answer 10

A measure of the energy required to raise the temperature of 1 kg of material by 1°C.

Question 11

The venturi effect in more detail

Answer 11

• A phenomenon observed in fluid dynamics.
• In fluids (such as wind) an increase in velocity when flowing through constricted spaces of cities is observed.
• This effect has been observed in major cities across the world as predominant winds are forced through a dense network of high-rise buildings.
• During calm and clear nights when the UHI is at its greatest there is air movement from the cooler rural periphery into the warmer city centre.

Question 12

Precipitation and fog

Answer 12

. Urban areas can have higher rainfall levels because of a wide range of climatic factors relating to the urban form.
. Pollutants in the air lead to an increase in hygroscopic nuclei around which rain droplets can form leading to an urban fog

Question 13

Thunderstorm

Answer 13

. The intense heating and rapidly rising air leads to fast rates of convections and large thunderstorms can develop
. Associates lighting and heavy rainfall
. More a summer phenomenom

Question 14

Walkie Talkie

Answer 14

. 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