Urban climate - section 4

what is weather

the state of the atmosphere at any particular moment in time (usually a few days to a week)

what is a microclimate

the distinctive climate of a small area

what is the problem with the walkie talkie building in london

• flares out at the top and causes the light to be reflected onto the street

• heat is concentrated

describe the urban heat island

• the temperature lowers as distance increases from the cbd

• highest temp in the cbd

describe how building material impacts the urban heat island

• concrete, bricks and tarmac absorb large quantities of heat in the day which is stored and slowly released at night

• highly reflective materials concentrate the heating effect in the surrounding streets by reflecting the energy downwards

what is an urban environment albedo

lower number= absorbing more heat

higher number= reflective

how do industries influence the urban heat island

• heat comes from industries, buildings and vehicles which all burn fuel

• air pollution from industries/vehicles creates a pollution dome which allows in short wave radiation but absorbs a large amount of outgoing radiation- also reflects it back to the surface

how does water influence the urban heat island

water falling onto surface is disposed of as quickly as possible

change the urban moisture and heat budget- reduced evapotranspiration- so more energy available to heat the atmosphere

how can the urban heat island change over time

• contrasts between urban and rural areas are greatest under calm, high pressure conditions

• heat islands develop better in winter

• urban-rural contrasts are more distinct at night

how does precipitation change with increased urbanisation

more condensation nuclei

more precipitation

more precipitation further down wind of the city

how does fog change with increased urbanisation

more fog

wind cant dissipate fog as easily

how do thunderstorms change with increased urbanisation

warmer conditions lead to more thunderstorms in cities

• urban areas enhance convection

• increased surface temperature provides more buoyancy

why is there increased convectional rainfall in urban areas

• urban heat island generates convection

• the presence of high- rise buildings and a mixture of building heights induces air turbulence- increased vertical motion

• water vapour from industrial sources and power stations act as hydroscopic nuclei and assist in raindrop formation

why is there higher precipitation in urban areas

• higher urban temperatures- encourages lower pressure over cities

• increased air pollution provides condensation nuclei

• generates convection- evapotranspiration due to high ground temperatures

• increased air turbulence- high rise buildings

• more water vapour from industrial sources and power station

describe how low pressure in urban areas leads to more precipitation

• surface winds are drawn from the surrounding rural areas

• air converges as it is forced over the high urban canopy

• This convergence leads to uplifting and cooling of air, resulting in condensation and increased precipitation.

how do pollutants in urban areas lead to more precipitation

• act as hydroscopic nuclei- assist with raindrop formation

• enhance the chance of lighting as the cloud droplets take on different electrical charges

what is the difference in downwind from urban to rural areas

urban areas have 20% greater downwind than rural areas

due to heating of surface and overlying air creating instability in the atmosphere- encourages air to rise

what causes fog

tiny water droplets suspended in the air

where does the thickest fog occur

in industrial areas where there are many pollution particles on which water droplets can grow

how are the types of fog classified

• according to the physical process which produces saturation or near-saturation of the air

when does radiation fog occur

in the winter- aided by clear skies and calm conditions

describe how radiation fog forms

• cooling of land overnight by thermal radiation cools the air close to the surface

• reduces the ability of the air to hold moisture- allowing condensation and fog to occur

• dissipate soon after sunrise as the ground warms and the air temperature rises, decreasing humidity. - exception to this is in high elevation areas where the sun has little influence in heating the surface

describe fog in cities

• increased along with industrialisation

• in 1700s London, there would have been 20 days of fog per year- in the 1800s it rose to 50 days per year

• particles act as condensation nuclei and encourage fog formation at night- under high-pressure weather conditions

describe the clear air acts of the 1950s

• resulted in a reduction in smoke production and particulate emissions

• decrease in the number of foggy days

describe fog in developing cities

fog increases as they continue to industrialise

e.g. New Delhi and Beijing suffer regular winter fogs

what is the impact of fog in cities

can cripple transportation networks and become hazardous to human health when they trap pollutants

what are thunderstorms

violent and heavy precipitation associated with thunder and lightning

how are thunderstorms formed

• convectional uplift under conditions of extreme instability

• cumulonimbus clouds develop up to the height of the tropopause where inversion produces stability

• updraught of air causes rapid cooling and condensation- leads to the formation of water droplets, hail and ice

• latent heat is released that further fuels the conventional uplift

• when the charge is high enough to overcome resistance in the cloud or atmosphere, discharge occurs to areas of negative charge from the cloud to the Earth

• lightning produces

• extreme temperatures generated cause a rapid expansion of the air which develops a shock wave- thunder

describe wind speed in urban areas

• increased friction- reduces the maximum wind speed

• can concentrate the wind- e.g. New York

describe how the Shard effects wind

wind can rush down building so it can be faster as the bottom of the building

canopy put in place to stop the rapid wind speed

describe wind direction in urban areas

• buildings direct wind upwards

• vortex of wind downwards

• strong wind currents above

• area between buildings has low pressure

• changes in pressure lead to strong currents

• venturi effect!

describe smog

a mixture of fog and smoke particles

common during industrial revolution

describe smog in 1952

responsible for more than 4,000 deaths

describe the temperature inversion in urban areas

a phenomenon where warm air traps cooler air at the surface, preventing pollution dispersal.

This can lead to increased smog and health issues.

describe LA’s problem with photochemical smog

high density of vehicles, frequency sunshine, topography that traps photooxidant gases at low levels

describe photochemical smog in Athens

located in a river basin so it is sheltered

why is photochemical smog a hazard during the anticyclonic conditions

one air has descended, it is relatively static owing to the the absense of wind

can persist for weeks during the summer

what is a primary pollutant

an air pollutant emitted direction from a source

what is a secondary pollutant

not directly emitted but forms when primary pollutants react in the atmosphere

describe carbon monoxide

colourless, odourless

poisonous to breath in

what are the sources of carbon monoxide

cigarette smoking

incomplete combustion of carbon containing fuels

what are the effects of carbon monoxide

reacts with haemoglobin in red blood cells

reduces the bloods ability to transport o2

impairs perception and thinking- leads to slow reflexes and headaches

describe nitrogen dioxide

• irritating gas

• gives photo chemical smog

• can be converted to nitric acid in the atmosphere

what are the sources of nitrogen dioxide

fossil fuels burning in motor vehicles

power and industrial plants

what are the effects of nitrogen dioxide

lung irritation and damage

HNO3 can damage trees, soils and aquatic life in lakes

corrodes metal and can damage fabrics

describe sulphur dioxide

• colourless, irritating

• forms from the combustion of sulphur contains fossil fuels such as coal and oil

what are the sources of sulphur dioxide

coal burning in power plants

industrial processes

what are the effects of sulphur dioxide

breathing problem- restriction of airways for people with asthma

reduces visibility- acid deposition can damage trees and aquatic life

can corrode metal and eat away stone of buildings

describe suspended particulate matter

particles and droplets that are small and light- remain suspended in the atmosphere

cause smoke, dust and haze

what are the sources of suspended particulate matter

burning coal in power and industrial plants

agriculture

construction

vehicles

what are the effects of suspended particulate matter

reduces visibility

damage to trees and aquatic life

corrodes metal

describe ozone

highly reactive and irritating

forms in the troposphere as a component of photochemical smog

what are the sources of ozone

chemical reactions with volatile organic compounds

emitted mostly by cars and industries

nitrogen oxides to form photochemical smog

what are the effects of ozone

breathing problems and irritation

reduces resistance to colds and pneumonia

damage to plants and trees

damages rubber and paints

what causes air pollution to vary

time of year

air pressure

what is photochemical smog

air pollution formed when sunlight reacts with pollutants

describe clean air acts

1956 london- smoke free zones

oxford- now- congestion charge and low emissions zones

describe zoning of industry

higher building chimneys to emit pollutants above the inversion layer

describe air pollution in Mexico city

• high altitude- less o2

• higher temps- in a valley resulting in stagnant air and trapped pollutants, leading to larger smog issues.

• 7000 tonnes of pollutants every day

give examples of solutions to the air pollution problem in mexico city

• petrol stations stopped selling leaded fuel- less polluting but cost of converting cars was high

• Bus rapid transit was expanded- less reliance on cars and useful for tourists- needs a lot of funding

• Ecoparq- metered parking programme- good for generating government income- valets who reserve parking spaces lost their jobs- informal work

are the solutions to air pollution in mexico city working

not the most polluted city anymore

still has a below average air quality

8% of the city’s annual budget is spent on the green plan (US $1 billion)

why did the birmingham jewellery quarter need resurgence

• reduced demand for goods during the blitz

• decline in the no. firms (8,000 in 1960s→ 600 by 1980s)

• multiple regeneration attempts

what was done to improve Birmingham’s jewellery quarter

• started in 2000s

• formed warehouses and factories converted into loft style apartments and townhouses- to attract new businesses and investment to the area

• canals cleaned up and turned into new public spaces- e.g. resturants and bars

what were the effects of Birmingham’s jewellery quarter regeneration

• increased rent prices

• improved safety

• changed economic demographic- more aimed at younger people

• traditional craft people are priced out

• loss of traditional character

why did Notting hill need gentrifying

• post ww2- housing crisis and slum conditions

• end of rent controls in 1957

• central location- led to a dead heart in london

• race riots- 1958- high tension

how was notting hill gentrified

• victorian homes were renovated into more expensive modern homes

• westway flyover was built- new wealthier residents began to buy and restore houses

• notting hill film- made the area more desirable- 1999

• high end retail replaced local businesses

what was the impact of notting hill gentrification

• displacement of long term residents- 46% decline in black british residents from 2001 to 2011

• demographic shift

• property value increased meaning locals were priced out

• Afro-caribbean culture was diluted- affected local culture

• antiques market- replaced chain stores

describe urban policies in Britain in 1979

• UDC’s- 13 developed

• UDC’s have wide ranging powers and resources aimed to lever investment from the private sector

• faster regeneration of inner city areas- created thousands of jobs from the buildings created

• social inequality as it mainly attracts private investment and many original local residents couldn’t afford the new builds

describe urban policies in britain in 1986

• inner city initiatives- ran by the inner city task forces and the city action teams

• aim was to improve the economic environment and stimulate work on developments- e.g. environmental and recreational

• stimulated economic growth which encouraged new business

• uneven development as regeneration was only in certain regions

describe urban policies in britain in 1991

• city challenge- funding by competitive bids

• emphasis on change from unelected boards- partnerships with private sector and local communities

• encourages partnership work and coordinated regeneration as it involved local authorities, private businesses and voluntary work

• social inequality due to equally deprived areas missing out if they didnt have a high bidding

describe urban policies in britain in 1999

• english partnerships- EPs

• aim to support high quality sustainable growth in England

• responsible for land acquisition and major development projects

• long term investments- developments occurred over many years

• emphasised private investment so it prioritised profitable investments rather than what the local area needs

describe urban policies in britain in 2009

• new homes bonus- promotes house building

• bonus used as an incentive to local authorities to accept housing growth- councils received double the council tax per home for 6 years

• encouraged housing development due to financial incentives

• linked to housing number and not local need so it could increase social inequality between council areas

describe urban greening as a strategy to manage the urban heat island

natural cooling effect- lowers temperatures in urban parks

act as carbon stores and reduces flooding

describe sky view factor as a strategy to manage the urban heat island

• relative openness between buildings and in open areas

• if streets are at a perpendicular angle to prevailing wind there is less ventilation

describe green roofs as a strategy to manage the urban heat island

• can reduce roof temps by 20-40 degrees on a sunny day

• reduces rainfall runoff and increases biodiversity

describe cool surfaces as a strategy to manage the urban heat island

• roofs built from materials with high solar reflectance or albedo

• stores less solar energy during the day- leads less heat to emit into the atmosphere

describe how the urban heat island is a matter of concern in terms of energy

strain on the supply of energy for air conditioning

describe how the urban heat island is a matter of concern in terms of health

• extreme heat can cause exacerbated health conditions- e.g. heat stroke, asthma and organ damage

• vulnerable groups are more affected

describe how the urban heat island is a matter of concern in terms of air pollution

chemical reactions that produce ozone layer and smog are accelerated by high heats

lower wind speeds keep pollution trapped in the city

describe how the urban heat island is a matter of concern in terms of water

increased consumption by residents and businesses

can lead to water usage restrictions

evapotranspiration rates increase so more take up by plants and trees

describe how the urban heat island is a matter of concern in terms of monuments

higher rate of deterioration due to increase temperature based chemical weathering