Urban Climates
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- Created by: Evie :)
- Created on: 11-03-22 18:04
What is a microclimate?
The climate of a very small or restricted area
This usually differs from the climate of the surrounding area
This usually differs from the climate of the surrounding area
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what does Albedo mean?
The proportion of the incident light or radiation that is reflected back into the atmosphere by a surface
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What is particulate air pollution?
Air pollution caused by particles and gases mainly from the combustion of fossil fuels
(smoke out of cars)
(smoke out of cars)
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What is photochemical pollution
Exhaust fumes (NO2) reacting with sunlight forming airborne particles and ground level ozone- smog
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What is temperature inversion?
This is when the temp increases with height and traps pollution at lower layers of the atmosphere
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What is the urban heat island?
The zone around an urban area that is significantly warmer than its surrounding rural areas due to human activities
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What is the urban climate dome?
Urban areas create their own climates (microclimates) where weather can be different to the surrounding areas
This dome can extend upwards into the atmosphere up t 300m and can influence further microclimates --> downwind
This dome can extend upwards into the atmosphere up t 300m and can influence further microclimates --> downwind
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Urban effects on climate:
Temperature
Temperature
temps are higher in urban areas
0.5-0.8 degrees higher than nearby rural area- annual mean
0.5-0.8 degrees higher than nearby rural area- annual mean
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Precipitation
precipitation is higher in urban areas
annual quantity is 5-10% higher than in rural areas
annual quantity is 5-10% higher than in rural areas
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relative air humidity
lower in urban areas
annual mean is 6% lower than in rural areas
annual mean is 6% lower than in rural areas
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Visibility
Lower in urban areas
100% increase in amount of fog winter
30% in summer
100% increase in amount of fog winter
30% in summer
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Wind speeds
Lower in urban areas
annual wind speeds 20-30% lower
annual wind speeds 20-30% lower
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Radiation
lower in urban areas
Total UV at surface is 15-20% lower than in rural areas
Total UV at surface is 15-20% lower than in rural areas
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Pollution
Higher in urban areas
100% increase in dust particles compared to in rural areas
100% increase in dust particles compared to in rural areas
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Reasons for the Urban heat island effect:
Anthropogenic heat sources
(human activities)
Anthropogenic heat sources
(human activities)
Central heated buildings
Air con
vehicles
Peoples bodies generate heat
Air con
vehicles
Peoples bodies generate heat
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Air pollution
Caused by industry/ vehicles
This creates a pollution dome which allows in short wave radiation but stops a large amount of outgoing radiation
This creates a pollution dome which allows in short wave radiation but stops a large amount of outgoing radiation
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Drainage
In urban areas there is less surface water evaporating, as water falling is disposed of quickly through artificial drainage methods
normally water sits on surface and heat energy from sun would heat water and evaporate it, this energy remains in the urban
normally water sits on surface and heat energy from sun would heat water and evaporate it, this energy remains in the urban
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Lower albedo
surfaces in tne city tend to be less reflective (e.g, concrete, bricks, tarmac), which means they have a low albedo
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How to tackle the UHI
- urban greening
- energy efficiency
- building spacing
- insulating houses
- green roofs
- energy efficiency
- building spacing
- insulating houses
- green roofs
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..........
- light coloured roofs
building with glass to reflect heat down
- planting trees to take in co2
- cool surfaces
building with glass to reflect heat down
- planting trees to take in co2
- cool surfaces
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What are the health impacts of the urban heat island?
As temperatures rise during summer using transport systems can become very uncomfortable
Babies and elderly are most vulnerable
(passengers are advised to carry bottled water in London)
Babies and elderly are most vulnerable
(passengers are advised to carry bottled water in London)
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What are the environmental impacts of the UHI
- Higher temperatures means more water is being used by people drinking more or businesses/this can lead to water shortages and restrictions
- more air con is used, so more electric
- more air con is used, so more electric
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........
- There are higher evapotranspiration rates from plants
- tropical insects can thrive
- more pollution becomes trapped, leading to smog conditions
- tropical insects can thrive
- more pollution becomes trapped, leading to smog conditions
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Case study: Walkie talkie building/ melting cars
What is special about this building?
What is special about this building?
The concave shape of the building means a large amount of sunlight is reflected into a small area
The reflection effect lasts around 2 hours per day and it is present for 2-3 weeks due to the changing position of the sky
The reflection effect lasts around 2 hours per day and it is present for 2-3 weeks due to the changing position of the sky
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What has been done to combat the problem of the light reflection?
Netting was installed whislst a permanent solution of 'brisole soliel' (reduces heat gain in buildings) and aluminium fins was erected
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Urban climate
reasons for higher rainfall
reasons for higher rainfall
- Tall skyscrapers cause more orographic rain (more rain is created as buildings deflect moisture laden wind upward- air carrying moisture)
- UHI intense ground heating causes rapid evapotranspiration, resulting in cumulus cloud formation
- UHI intense ground heating causes rapid evapotranspiration, resulting in cumulus cloud formation
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reasons for lower humidity
there is less evaporation of water from the surface and higher temperatures and these both reduce relative humidity
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Why is there lower visibility
- Industrialisation/ air pollution
- Dust particles in cities act as condensation nuclei( tiny particles), encouraging fog formation at night under high pressure conditions
- Dust particles in cities act as condensation nuclei( tiny particles), encouraging fog formation at night under high pressure conditions
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Why is there more thunderstorms
They are associated with hot, humid air which is in cities and these are more likely in summer months
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Wind speeds in urban areas
How do city surfaces affect wind speeds
How do city surfaces affect wind speeds
The surfaces of cities are uneven due to varying heights of buildings, creating frictional drag which lowers overall wind speeds
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How does the UHI have an effect on wind speeds
On calm and clear nights the UHI creates low pressure compared to surrounding areas, resulting in localised winds
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How does the wind travel around single, tall buildings
It travels up and over
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How does wind travel around widely spaced buildings
They act as single buildings and it travels over
-->
-->
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How does wind travel around narrow spaced buildings
some wind travels over but the flows interfere
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How does wind travel around buildings spaced very close together
Wind skims over the top
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What is wind channelling
Wind redirected down long straight canyon like streets where there is less friction(urban canyon)
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What is the Venturi effect
The squeezing of wind into a narrower gap resulting in a pressure decrease and an increase in wind speed/ Wind cueing to get through a gap then speeding up when it gets through the gap
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Case study:
What is the issue with the building at Bridgewater Place in Leeds
What is the issue with the building at Bridgewater Place in Leeds
Strong wind causes dangerous walking conditions near the building/there is an issue of wind caused by down draft, as there are no other large buildings nearby(it's alone) Wind is channelled down the building and it is forced down
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Where is the wind formed here?
At the buildings foot, near the road
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How could strong winds have been prevented here?
- Building it at a 90 degree angle, so the curved side faces the wind
- Vertical wind turbines would help to reduce wind energy
- Vertical wind turbines would help to reduce wind energy
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What has been done to control the wind?
- Wind baffles were installed ( grass screens on the side of the path)
- wind deflectors placed above the road
- There is a canopy above the first floor of the entrance
- wind deflectors placed above the road
- There is a canopy above the first floor of the entrance
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Why is there carbon monoxide in cities and what are the impacts?
It is produced by the incomplete combustion of fuel (90% from road transport)
This affects the transport of oxygen around the body by blood
This affects the transport of oxygen around the body by blood
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What are the causes and effects of nitrogen dioxide in cities?
produced by fuel burning processes (industry and transportation)
This causes photochemical pollution (No2 reacting with sunlight)
No2 inflames the lining of the lungs and contributes to the weathering of buildings from acid rain
This causes photochemical pollution (No2 reacting with sunlight)
No2 inflames the lining of the lungs and contributes to the weathering of buildings from acid rain
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What are the causes and effects of particulate matter in cities?
They are produced from tiny particles from combustion
This can settle in lungs causing health problems
This can settle in lungs causing health problems
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What are the causes and effects of sulphur dioxide in cities?
Caused by burning materials which contain sulphur or fuels(oil or coal)
This causes people to cough and their airways can be narrowed
Causes acid rain
This causes people to cough and their airways can be narrowed
Causes acid rain
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Describe the urban temperature inversion
Warm air sits at the top, above the city
Cool moist air is trapped under the warm air
Air pollution lingers over the city
Dense cool air descends and settles on the valley floor
Cool moist air is trapped under the warm air
Air pollution lingers over the city
Dense cool air descends and settles on the valley floor
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How can air pollution levels be reduced in cities?
- fewer cars/public transport
-using electric cars
- planting trees
- using renewable energy/electricity
-Not over using air con
-using electric cars
- planting trees
- using renewable energy/electricity
-Not over using air con
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What is a congestion charge?
A way to discourage people from driving so there are less emissions and there is a charge to drive in the city centre
In London centre ULEZ (£15 per day, 7am-10pm)
This applies to cars running on fuel
In London centre ULEZ (£15 per day, 7am-10pm)
This applies to cars running on fuel
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What are the changes in Londons public transport?
Double decker buses are now hybrid (half electric, half fuel powered)/ single deckers are 0 emission
these reduce the quantities of pollution emitted into the atmosphere
these reduce the quantities of pollution emitted into the atmosphere
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Other cards in this set
Card 2
Front
what does Albedo mean?
Back
The proportion of the incident light or radiation that is reflected back into the atmosphere by a surface
Card 3
Front
What is particulate air pollution?
Back
Card 4
Front
What is photochemical pollution
Back
Card 5
Front
What is temperature inversion?
Back
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