1.5 Urban climate Flashcards
What are the 3 main features of an Urban climate
- Urban heat island effect
- Increased extreme weather events
- Reduced air quality
What is the Urban heat island effect
The idea that urban areas experience higher temperatures than rural areas, most prominently on summer nights (London is 10 degrees warmer)
What causes the urban heat island effect
- Low albedo surfaces
- Increased air pollution (high populations)
- Lack of plants and evapotranspiration
Give some economic, social and environmental reasons why the urban heat island effect is an issue
- Increased strain on energy and water supply
- The “walkie talkie” was melting cars
- Uncomfortable side effects like heatstroke
- Prolong growing season (allergies)
- Prolonged animal survival causes overpopulation and potential for harmful algae blooms to grow
- Increased risk of extreme weather
What are some ways we can reduce the urban heat island effect
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)
What are the 4 types of extreme weather that urban areas face and why
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
Who do urban areas have higher levels of storms
Storms are low pressure weather systems, which form under hot, humid conditions, therefore the urban heat island encourages their formation
Why do urban areas have more wind (naturally)
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
Why do urban areas have more wind (architecturally)
Wind speeds are generally lower in urban areas, however some buildings may change this
- Buildings expert a powerful frictional drag on the air around them, creating turbulence and wind
- Urban canyons (streets flanked by buildings) increase the Venturi effect, as wind is forced into narrow spaces
- 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)
Give an example of somewhere where wind has been changed by buildings
The Burj Khalifa (830m tall) is built orientated to prevailing wind and has softened edges to prevent vortices
Why do urban areas have higher levels of Cloud coverage and rainfall
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
Why do urban areas have higher amounts of thunderstorms
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
Why is air quality worse in urban areas
Because of the combustion of fossil fuels
Give 4 examples of urban pollutants
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
What are some things caused by urban air pollution
- Health problems and sickeness
- Death
- Smog
What is smog and what causes it
Photochemical smog is a mixture of pollutants that forms when NO2 and VOC’s react to sunlight and create a brown haze above cities
What is an inversion layer
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
Give an example of an incident related to an inversion layer with context
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
Give 3 examples of pollution reduction policies
Clean air acts
Vehicle control - £15 a day London congestion charge
Zoning of industry - build high chimneys, don’t locate in city centre etc.
Give some context for the UK clean air act
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
