Urban Heat Islands

Question 1

What is an urban heat island?

Answer 1

A patchwork of microclimates within an urban area

Question 2

What are peaks associated with?

Answer 2

Industry

City centre

Question 3

What are troughs associated with?

Answer 3

Parks
Reservoirs
Rivers

Question 4

What is the intensity of the uhi?

Answer 4

The max difference between the temp of the rural area and peak urban temp

Question 5

What factors affect the intensity and nature of the uhi?

Answer 5

Weather conditions
Season
Time of day

Question 6

Which climatic conditions tend to increase the intensity?

Answer 6

High pressure systems with clear nights and still,sunny dyas

Question 7

What are the 5 main factors influencing islands?

Answer 7

Anthropogenic heat 
Buildings - height and arrangement 
Buildings - materials 
Presence of water 
Pollutants

Question 8

What are 2 secondary influences?

Answer 8

Wind

Relief

Question 9

Explain anthropogenic heat

Answer 9

Vehicles, central heating, air conditioning and industrial activity inject heat into the canopy and upper boundary layer

Question 10

Explain buildings - height and arrangement

Answer 10

Radiation is reflected off many surfaces with each one absorbing some energy and warming up (low sky-view factor)
Multiple reflections reduce the albedo so built up areas have a lower albedo than rural areas

Question 11

Explain buildings - materials

Answer 11

Concrete = 1/3 of specific heat capacity of wet mud so that for a given input of energy concrete will heat up more quickly

Vegetation shades soil, so soil stores less heat

Urban areas are largely covered by tarmac which , as a dark coloured surface, absorbs heat in the day and releases the heat slowly over night

Question 12

Explain presence of water

Answer 12

Surplus heat = latent/sensible
Latent = evaporates water as and doesn’t raise air temp
Sensible = heat left over from evapotranspiaration heats atmosphere
Urban = less surface water so less heat used in evaporation. Most surplus heat is used as sensible heat to warm the atmosphere
Urban = 85% of total heat used to raise temp of air
Forests = 25%

Question 13

Explain pollutants

Answer 13

Dust and carbon particles are hygroscopic pollutants which act as condensation nuclei and = lead to the formation of cloud/smog which can create a pollution dome
Dome = reduces insolation is day so may trap outgoing radiation at night

Question 14

Explain wind

Answer 14

Usually there is a lack of strong winds in urban areas to disperse heat

Question 15

Explain relief

Answer 15

EG - Sheffield and Mexico City
Usually = Decrease in temp with altitude
Anticyclones = cool air will drain into low lying areas

Question 16

What are the key terms that need to be used when explaining associated diagrams?

Answer 16

Peak 
Secondary peak 
Cliff 
Plateau 
Trough