Urban Climate

Question 1

How does vegetation affect temperature?

Answer 1

• in areas with dense vegetation, the air is cooler
• in areas with sparse vegetation, the air is warmer

Question 2

What is an urban heat island?

Answer 2

A metropolitan area which is significantly warmer than the surrounding rural areas.

• London can be 6 degrees warmer than the surrounding countryside

Question 3

What factors affect the urban heat island?

Answer 3

• Albedo effect - darker surfaces absorb heat and lighter surfaces reflect heat. Many urban surfaces are dark eg. tarmac, roofs, so heat is absorbed
• Structure - the complex three-dimensional structure of urban areas means that they are less ventilated, heat can get trapped within streets
• Sources of heat - vehicles, air conditioning, transport all release extra heat into urban environments
• Building materials - materials like concrete absorb and store heat
• Vegetation - keeps an area cool by transpiration, moves heat energy from the surface into the atmosphere, less vegetation in urban areas
• Water - surface water keeps an area cool, evaporation from surface water moves heat from the ground into the atmosphere, more lakes/ponds/rivers in rural areas. Rainfall in urban areas is often channelled underground into drains or sewers

Question 4

Why is there increased precipitation in urban areas?

Answer 4

• Urban areas in the UK increase precipitation by 10-20%
• UHI causes convection currents - warm air rises and condenses - cumulus clouds form and rain
• low pressure environments created by rising air forced to rise over the tall urban canopy
• city pollution - increases cloud formation, pollutants act as hygroscopic nuclei which assist in raindrop formation
• water vapour - large amounts of water vapour produced from industry and power stations

Question 5

why do urban areas experience more fog than rural areas?

Answer 5

• 100% more fog in winter in urban areas than rural areas
• lower wind speeds - fogs are not easily dispersed
• pollution - more hygroscopic nuclei for water droplets to form, prevents suns rays from penetrating ground so fog is not dispersed
• warmer air - needs more cooling to reach dew point

Question 6

why do urban areas experience more thunderstorms than rural areas?

Answer 6

• Thunderstorms form in hot humid air and are characterised by heavy precipitation, thunder and lightning.
• UHI - warm air holds more moisture, more rainfall, convectional rainfall
• Water vapour and condensation nuclei from industry and vehicles creates intense precipitation and thunderstorms
• The extreme temperatures cause a rapid expansion of air which develops a shock wave, creating the thunder sound
• buildings - tall buildings increase speed of rising air, increased electrical charge due to rapid rising air and friction leading to lightning

Question 7

how does the urban layout lead to high velocity winds?

Answer 7

Towards the city centre, buildings get taller and streets get narrower. Winds are squeezed into increasingly restricted streets producing the Venturi effect. Low pressure behind buildings and high pressure in front of buildings and wind is sucked from high to low pressure ‘Venturi effect’

Question 8

how are winds affected by a single building?

Answer 8

can disrupt air flow leading to Eddie currents - air is sucked around building from high to low pressure

Question 9

Why is there smog in urban areas and what is the problem with smog?

Answer 9

Increased smog due to factories and consumerism

• leads to respiratory illnesses
• visibility on roads decreases

Question 10

What is a temperature inversion?

Answer 10

Normally, temperature decreases with altitude. When temp is inverted, cold air sinks to the bottom of the valley (usually in high pressure areas), so air condenses and forms fog. This traps cool, moist air under warm air, which traps pollution

Question 10

example of smog in London

Answer 10

‘pea souper’ 1952
A thick smog in London which led to the death of 12,000

Question 11

What are the global patterns of air pollution?

Answer 11

Low levels of air pollution in America - less manufacturing

Asia/NEE’s most polluted - manufacturing industry

Nigeria - high pollution due to oil industry

Eastern Europe - due to prevailing wind and pollution moving Eastwards

Question 12

What is advection fog?

Answer 12

Advection fog forms as warmer, moist air moves sideways over a cold ground. The air is cooled to saturation by the cold from the ground below cooling the air above.

Question 13

What are anticyclones?

Answer 13

An anticyclone is formed when a high-pressure region is surrounded by low pressure areas. This high pressure is formed because of lower temperatures compared to adjoining areas. So now the winds blow outward from the high pressure zone towards the low pressure area creating a high-pressure, cloudless area with radiation fog

Question 14

What is particulate air pollution?

Answer 14

caused by the release of particles and noxious gases. Emissions can occur naturally but are largely caused by combustion of fossil fuels

Question 15

What is photochemical smog?

Answer 15

Photochemical smog is a mixture of pollutants that are formed when nitrogen oxides and volatile organic compounds (VOCs) react to sunlight, creating a brown haze above cities.

Question 16

How is carbon monoxide produced?

Answer 16

road transport responsible for 90% emissions in the UK

Question 17

How is nitrogen dioxide produced?

Answer 17

road transport estimated for 50% emissions

Question 18

How is particulate matter produced?

Answer 18

power stations and vehicle exhausts eg. dust, ash, pollen

Question 19

How is sulpher dioxide produced?

Answer 19

coal and oil burning by industry eg. power stations

Question 20

What are the main impacts of air pollution?

Answer 20

• inflame lining of lungs and affect transport of oxygen around the body
• headaches, eye irritation, coughing
• acid rain causing weathering of buildings and damage to plants

Question 21

What strategies are used to reduce air pollution?

Answer 21

• bus/car pooling lanes
• greater provision for cyclists
• park and ride schemes
• banning cars from driving on certain days
• mass transit systems eg. metro link

Question 22

What strategies are used to reduce air pollution in London?

Answer 22

• congestion charge (2003) - a fee that vehicles must pay to enter a designated area in the city at specific days or times, £15 per day
• ULEZ - introduced April 2019 - vehicles entering a specific area must meet specific emission standards ( based on Euro emissions standards), ULEZ zone includes most of the city centre and was expanded in 2021 bounded by the A406 and the A205, £12.50 per day
• boris bikes

Question 23

How successful have air pollution reduction schemes in London been?

Answer 23

• 44% reduction in NO2 levels in central London since 2021
• revenue from congestion charge and ULEZ in 2020 exceeded £300 million

Question 24

Facts about air pollution in London?

Answer 24

• 7.9 million Londoners (95% of the population) live in areas exceeding the limit of damaging particulates (PM2.5) by 50%
• 37 out of 43 zones across the UK are in breach of pollution limits

Question 25

Why is London at higher risk of flooding?

Answer 25

• 15% London is on the floodplain of the Thames and 49 railway stations, 75 underground stations and 10 hospitals are at risk
• climate change means that sea levels are rising and low pressure storm events are more frequent
• more fluvial flooding from torrential rain, because London is between the high and low pressure belt causing heavy rainfall
• storm surges are more frequent as low pressure and high tide combined cause flooding

Question 26

Strategy for managing flood risk in London?

Answer 26

Thames estuary 2100 plan

• protects 1.3 million people and £275 billion worth of property
• overall cost - £16.2 billion
• includes Thames barrier and 8 other flood barriers, over 350km walls and embankments and 400 other structures eg. flood gates and pumps
• protect London, Essex and Kent from regular flooding

Question 27

Facts about dereliction in London?

Answer 27

• more than 22,000 commercial properties have been vacant for at least 6 months
• 6700 acres of land remains undeveloped, despite having planning permission
• 97% of new dwellings are built on previously developed land (brownfield sites)

Question 28

What are the advantages of using brownfield sites?

Answer 28

• cheaper land
• green space not used up, UHI, urban drainage, habitat loss
• high crime rates decrease
• decreased contaminated and dangerous land