1.5 Urban climate

Question 1

What are the 3 main features of an Urban climate

Answer 1

1. Urban heat island effect
2. Increased extreme weather events
3. Reduced air quality

Question 2

What is the Urban heat island effect

Answer 2

The idea that urban areas experience higher temperatures than rural areas, most prominently on summer nights (London is 10 degrees warmer)

Question 3

What causes the urban heat island effect

Answer 3

1. Low albedo surfaces
2. Increased air pollution (high populations)
3. Lack of plants and evapotranspiration

Question 4

Give some economic, social and environmental reasons why the urban heat island effect is an issue

Answer 4

1. Increased strain on energy and water supply
2. The “walkie talkie” was melting cars
3. Uncomfortable side effects like heatstroke
4. Prolong growing season (allergies)
5. Prolonged animal survival causes overpopulation and potential for harmful algae blooms to grow
6. Increased risk of extreme weather

Question 5

What are some ways we can reduce the urban heat island effect

Answer 5

Cool surfaces - reflect 80% of suns energy

Green roofs - reduce temps by 4 degrees (reduce surface runoff, and act as insulators)

Urban greening (plant trees)

Question 6

What are the 4 types of extreme weather that urban areas face and why

Answer 6

Wind and low pressure

Higher levels cloud and rainfall

Thunderstorms

Fog (higher because inner cities have more air particles, it increases with industrialisation) and SMOG

Question 7

Who do urban areas have higher levels of storms

Answer 7

Storms are low pressure weather systems, which form under hot, humid conditions, therefore the urban heat island encourages their formation

Question 8

Why do urban areas have more wind (naturally)

Answer 8

Urban areas can be split into the Urban canopy and Urban boundary.

As warm air rises over the Urban boundary, it draws in heat and air from other areas, creating an area of low pressure, causing more wind

Question 9

Why do urban areas have more wind (architecturally)

Answer 9

Wind speeds are generally lower in urban areas, however some buildings may change this

1. Buildings expert a powerful frictional drag on the air around them, creating turbulence and wind
2. Urban canyons (streets flanked by buildings) increase the Venturi effect, as wind is forced into narrow spaces
3. Wind pressure gradients are set up on the windward (high pressure) and leeward (low pressure) side. Wind moves from high pressure to low pressure zones, causing a steep pressure gradient (hence strong winds)

Question 10

Give an example of somewhere where wind has been changed by buildings

Answer 10

The Burj Khalifa (830m tall) is built orientated to prevailing wind and has softened edges to prevent vortices

Question 11

Why do urban areas have higher levels of Cloud coverage and rainfall

Answer 11

Urban areas have higher levels of pollution and therefore more/larger hygroscopic nuclei, which encourages cloud formation

Increased rainfall is caused by this the increased pollution, cloud coverage and urban heat island effect

Question 12

Why do urban areas have higher amounts of thunderstorms

Answer 12

Storms are low pressure weather systems, which form under hot and humid conditions, provided by the urban heat island effect and pattern of wind movement

Question 13

Why is air quality worse in urban areas

Answer 13

Because of the combustion of fossil fuels

Question 14

Give 4 examples of urban pollutants

Answer 14

CO - colourless odourless gas caused by fossil fuels. Affects transport of oxygen around blood (nausea)

NO2 - Most dangerous, cause brown hazes above cities, inflames the lining of lungs (asthma)(acid rain)(death)

PM - Fine grade materials like smoke and dust in air that settles in airways and causes breathing problems

CO2

Question 15

What are some things caused by urban air pollution

Answer 15

1. Health problems and sickeness
2. Death
3. Smog

Question 16

What is smog and what causes it

Answer 16

Photochemical smog is a mixture of pollutants that forms when NO2 and VOC’s react to sunlight and create a brown haze above cities

Question 17

What is an inversion layer

Answer 17

When warm air acts as a lid and traps the cold polluted air underneath it, forcing it back down, causing a smog to built up

Question 18

Give an example of an incident related to an inversion layer with context

Answer 18

The London Smog 1952, lasted for 4 days caused by an anti-cyclone + inversion layer

12,000 people died
100,000 have lifelong respiratory issues
People could only see 1-yard infront

Question 19

Give 3 examples of pollution reduction policies

Answer 19

Clean air acts

Vehicle control - £15 a day London congestion charge

Zoning of industry - build high chimneys, don’t locate in city centre etc.

Question 20

Give some context for the UK clean air act

Answer 20

The acts were established in 1956 to introduce smoke-free zones across the UK, to reduce air pollution

Each UK authority has to assess pollution in their area, and if it falls below, it becomes a designated AQMA

50% of UK households now live in smoke free zones