Urban Climate

Question 1

Define an urban microclimate:

Answer 1

When the climate in an area differed from its surroundings in an urban dome.

Question 2

Define an urban heat island:

Answer 2

When an urban area has a higher temperature than its surroundings and rural counterparts.

Question 3

Give three ways how urban heat islands form:

Answer 3

• Infrastructure materials having a low albedo (reflectivity of solar radiation) = shortwave solar radiation is absorbed and retained in buildings, roads and streets = Heat is let out at night = creating warmer temperatures than in surrounding rural areas
• Air pollution acts as artificial clouds = keeps in shortwave radiation
• Buildings, cars, buses and densely packed people give off heat

Question 4

Give 4 issues with urban heat islands:

Answer 4

• Can become extremely hot during heatwaves = increase likelihood of health problems, e,g, heat stroke, death
• Can increase air pollution through photochemical pollution
• Workplaces and schools can be disrupted during heatwave
• Extra strain on resources (e.g. energy, water)

Question 5

Give three ways to manage urban heat islands:

Answer 5

• Increase albedo of infrastructure material (so more solar radiation is reflected and less is absorbed)
• Increase green spaces
• Green roofs
• ENcourag energy efficient air systems
• Neighbourhood watch schemes

Question 6

How do urban heat islands impact precipitation?

Answer 6

• Higher urban temperatures cause convection currents of low pressure = rainfall (due to high evapotranspiration)

Question 7

How do high-rise buildings impact precipitation?

Answer 7

• Cause air turbulence to be highly vertical

Question 8

How does pollution impact precipitation?

Answer 8

• Increases cloud formation (pollution particles attract water vapour gases)

Question 9

How do industrial factors impact precipitation?

Answer 9

Industrial waste in the form of water vapour is pumped into the local atmosphere = cloud formation

Question 10

What is the problem with urban fog?

Answer 10

• Has trapped pollutants that can cause health issues, such as asthma and respiratory problems
• Reduces air quality and can have negative environmental effects (e.g. stunting tree growth)

Question 11

How do urban thunderstorms occur?

Answer 11

• Convectional uplift
• Condensation occurs forming water droplets, hail and ice
• Mixes with uplift, creating a charge
• Negative charges cause lightening
• Air temperatures rise, causing air to expanse creating the sound of thunder

Question 12

Give 3 ways how urban farms can affect wind speeds and directions:

Answer 12

• Urban infastrucute (especially buildings) cause frictional drag
• Tall buildings can slow down wind and channel air downwards into straight streets below = urban canyon
• Two buildings close together cause channelling of the air = wind speeds increase due to pressure = Venturi effect

Question 13

Give 4 ways to manage photochemical smog:

Answer 13

• Political legislation = UK’s clean air act of 1956 and 1993 = policies to reduce pollutants and emissions
• Zero emissions or low emission zones
• Car-free days = raises awareness of pollution over actually reducing emissions
• Banning petrol/diesel cars and offer green (electric) cars

Question 14

Why is the urban heat island effect stronger at night?

Answer 14

Urban surfaces continue to release heat that they absorbed during the day.

Question 15

Why is the urban heat island effect stronger in summer?

Answer 15

There is more solar radiation in summer, so urban areas absorb more heat.

Question 16

Why is the urban heat island effect stronger when there is an anticyclone?

Answer 16

• Anticyclones cause clear skies and low winds.
• No clouds mean more solar radiation reaches and heats the ground.
• Low winds mean warm air isn’t blown away.

Question 17

What are the four main causes of the urban heat island effect?

Answer 17

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

Question 18

How does absorption of heat by urban surfaces cause the UHI effect?

Answer 18

• Concrete, brick, tarmac surfaces absorb and store heat from the sun during the day.
• Heat is slowly released as long wave radiation.

Question 19

How does air pollution cause the UHI effect?

Answer 19

• Air pollution from cars and factories increases cloud cover over the city, creating a ‘pollution dome’.
• Traps outgoing heat radiation and reflects it back.

Question 20

How does heat from human activity cause the UHI effect?

Answer 20

Cars, factories, offices, central heating, air conditioning units and people all release heat.

Question 21

How does less evaporation cause the UHI effect?

Answer 21

• Rain water is quickly removed by drainage systems
• Little surface water to evaporate

Question 22

What is the canyon effect?

Answer 22

When wind hits the face of a building and is deflected.

Question 23

What are the two main causes of intense rainfall and thunderstorms in urban areas:

Answer 23

• Convectional uplift
• Condensation nuclei

Question 24

How does convectional uplift increase the precipitation and thunderstorms in urban areas?

Answer 24

• UHI effect means air in urban areas in warm and moist, holding a lot of water.
• The warm, moist air rises (convectional uplift) and cools, causing the water vapour to condense and cause rain

Question 25

How does condensation nuclei increase the precipitation and thunderstorms in urban areas?

Answer 25

- Urban areas generate huge amounts of dust and pollution particles in the air (condensation nuclei) - Condensation nuclei trigger water molecules to condense around them - Encourages clouds to form.