urban climate Flashcards
urban heat island effect?
urban heat island effect —> urban areas being warmer than surrounding rural areas
4 main causes of UHI effect?
ABSORPTION OF HEAT BY URBAN SURFACES:
- Surfaces in urban areas have low albedo and tend to be much less reflective so they absorb a lot of heat —> concrete, brick and tarmac surfaces absorb and store heat from the sun during the day —> this heat is slowly released as long wave radiation at night
- Rural areas tend to have more grass —> greater albedo —> temperatures lower
AIR POLLUTION: Air pollution from cars and factories increases cloud cover and creates a ‘pollution dome’ (layer of pollution over the city) —> both of these trap outgoing heat radiation and reflect it back to the surface
HEAT FROM HUMAN ACTIVITY:
- Cars, factories, offices, central heating, air conditioning units and people themselves all release heat
- People release heat so cities with large populations will be warmer —> positive feedback loop —> people will turn air conditioning on —> releases hot air into atmosphere —> temperatures rise
LESS EVAPOTRANSPIRATION: When it rains, water is quickly removed by drainage systems —> less evapotranspiration —> less cooling effect from water —> higher temperatures
Day and night:
- The UHI effect is stronger at night
- Urban daytime temperatures are on average 0.6 °C warmer than surrounding rural areas but at night time, temperatures in urban areas can be 3-4 °C warmer than rural areas —> rural areas cool down at night, but urban areas don’t cool as much because urban surfaces continue to release heat that they’ve absorbed during the day
Seasonally:
- UHIE is stronger in summer
- Average winter temperatures can be 2°C warmer, but average summer temperatures can be up to 5°C warmer in urban areas —> there’s more solar radiation in summer so urban areas absorb more heat
- UHIE is stronger when there’s an anticyclone —> anticyclones cause clear skies and low winds —> if there are no clouds, more solar radiation reaches and hits the ground —> low winds mean warm air isn’t blown away
how can the UHI effect be managed?
- increased vegetation —> plants absorb sunlight and reduce the amount of heat absorbed by buildings// trees also release moisture into the air through evapotranspiration —> cools the air down —> reduces need for air conditioning
- implementing cool roofs —> reflects more sunlight and absorbs less heat than standard roofs —> less heat transferred into buildings —> reduce need for air conditioning
- urban design —> e.g. using lighter coloured materials for buildings and roads and creating more open spaces
- energy efficient appliances —> less heat released by energy efficient appliances —> reduce overall heat production in urban areas
temperature peak, sink, plateau and cliffs?
temperature peak - the highest temperatures are found in industrial areas and in densely built up areas e.g. the CBD
temperature sink- pockets of cool air are found above parks and bodies of water (e.g. rivers or ponds)
temperature plateaus- areas within the city with the same land use generally have the same temperature
temperature cliffs- temperature can change rapidly when land use changes e.g. from inner city housing to CBD high rise buildings
wind in urban areas?
- If buildings are closely packed, the wind can skim over the top —> creates strong wind and turbulence around buildings
- Air is displaced upwards and around the sides of single buildings —> air is pushed down on the leeward side of the building —> a negative pressure is created that can be even more powerful than the positive pressure on the windward side
- Average wind speed is usually lower in cities than in rural areas —> tall buildings create friction that slows down the moving air
- There are areas where wind speed is 0 —> some areas are totally sheltered from wind by buildings
- Canyon effect —> you get powerful gusts of wind when wind is channelled down streets —> buildings on both sides of the street squeeze the wind
precipitation in urban areas?
what causes rain?
- other air masses —> warm air is less dense than cool air —> when they meet, the warm air is forced to rise —> air cools and condenses to form clouds —> frontal precipitation
- topography —> when warm air meets mountains, it is forced to rise —> air cools and condenses to form clouds —> orographic precipitation e.g. the pennines
- convection —> sun heats up the ground —> moist air rises —> air cools and condenses to form clouds —> convective precipitation
why is precipitation higher in urban areas?
- Precipitation is 5-15% greater in urban areas than in rural areas
- The rain is more intense and there are more thunderstorms in urban areas
- Urban heat island generates convection —> this heats up the ground —> moist air rises —> air cools and condenses to form clouds —> convective precipitation
- More pollution and dust in cities —> pollution and dust particles act as condensation nuclei and trigger water to condense around them —> clouds form —> rainfall
- The UHI effect means the air in urban areas is warm —> warm air can hold more water —> warm air rises —> as it rises, it cools —> the water vapour condenses to form clouds —> rainfall
fog in urban areas?
fog —> a thick cloud of tiny water droplets suspended in the atmosphere which restricts visibility
why do urban areas have more fog?
- Wind speeds are lower in urban areas so fogs are not so easily dispersed
- More pollution in urban areas —> acts as condensation nuclei for water droplets to form fog// presence of pollution prevents sun’s rays penetrating to the ground —> fog warms up instead —> fog not dispersed
why was there more fog in the past?
- industrialisation —> pollution from industrialisation —> pollution acts as condensation nuclei —> encourages fog formation
air pollution in urban areas?
- Particulates —> tiny pieces of solids and tiny droplets of liquids floating in the air
- More particulates are found in urban areas than in rural areas
- Pollution is bad as it creates fog and rain
Sources of particulates include:
- Vehicle exhausts - they produce very fine particulates —> about 80% of fine particulates in urban areas are from vehicle exhausts
- Burning of waste, cigarettes and fuel - this produces both fine and coarse particulates
- Construction, mining and quarrying - these activities produce coarse particulates
Issues caused by particulates?
- Particulates can cause health problems e.g. asthma and lung cancer —> coarser particulates are usually filtered out by the nose and throat so they can’t enter the body, but finer particulates (often called PM10) can enter the lungs
photochemical smog —> air pollution?
- Photochemical smog —> smog that is created by sunlight and dust/smoke particles reacting together to produce low level ozone which is very dangerous to health
- Photochemical smog is a problem in many cities e.g. LA —> It’s more common in places with hot and sunny climates because there’s more sunlight —> These locations often have a temperature inversion- when temperature in the atmosphere is warmer than below —> this means that all the pollution is trapped
- Urban areas experience twice as much CO2 and 7x more dust particles in their local atmosphere —> impacts health
ways to reduce air pollution?
congestion charging:
- People are charged if they use their vehicles in certain places at certain times —> reduces pollution by reducing road traffic
- In Central London congestion charging reduced traffic and emissions in the congestion zone by around 15% in its first year of operation ✅
- However, some people travel around the edge of zones to avoid being charged —> traffic increases in these areas —> so it just moves the problem to other areas ❌
pedestrianisation:
- Vehicles are restricted from entering certain places at certain times —> reduces pollution by reducing road traffic —> many cities have pedestrianised zones e.g. London ✅
- Pedestrianisation can lead to shops receiving fewer customers because people can only get to them on foot ❌
public transport improvements:
- Encouraging people to use public transport instead of their cars reduces pollution
- Improved bus services to make bus journeys cheaper, faster and more efficient e.g. many cities have introduced bus lanes so buses don’t get caught in traffic
- Park and ride schemes to make it easier to access public transport
- Trams and light railway services which run on lines, so they don’t get caught in road congestion e.g. The Metrolink in Manchester links the city centre to the suburbs —> the line to Bury and Altrincham has taken around 2.6 million cars off the roads
- Public transport improvements are often expensive e.g. construction of the Metrolink cost over £1 billion ❌
- New developments can cause problems e.g. park and ride schemes can shift traffic problems to rural areas —> park and ride scheme encourages commuters to drive to the edge of urban areas —> more traffic here ❌
other schemes reducing traffic:
- In Mexico City drivers are banned from using their cars one weekday per week, based on the last digit of their number plate e.g. number plates ending in 5 or 6 can’t be used on Mondays ✅ However, some richer households get around the system by buying two cars ❌
- Car sharing schemes encourage people making the same journey to share a car ✅ However, some people find car sharing inconvenient, or worry about sharing a car with a stranger ❌
larger scale ways to tackle air pollution:
legislation/laws:
- The UK Clean Air Acts of 1956 and 1968 reduced pollution by introducing smoke control areas where only smokeless fuels could be burned
- Introducing tall chimneys —> pollutants are dispersed higher in the atmosphere so they’re less harmful to people in the city
- The Road Vehicles Regulations reduce exhaust emissions by ensuring cars pass an emissions test in their MOT
- Throughout the UK, local authorities can issue fines to people who leave their engines running unnecessarily
alternative fuels:
- Petrol and diesel are replaced with cleaner fuels that pollute less e.g. biofuels are produced from plants ✅ However, growing the crops needed to make biofuels can reduce biodiversity e.g. biofuels need a lot of land to grow so it can lead to the clearing of other vegetation ❌
- Electric vehicles have lower emissions because they run off batteries, rather than conventional fuel ✅ Electric vehicles need recharge points and disposing the batteries can cause environmental problems ❌
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SUDS
Sustainable urban drainage systems (SUDS) —> using nature to manage water —> aims to minimise urban drainage issues e.g. decrease flooding, water pollution and drought in urban areas
Examples of SUDS?
- Water Butts- roof water collected in containers for use during dry seasons —> decrease drought// surface run off decreases —> less flooding/less pollutants entering river
- Bioswales (vegetated trenches around roads) —> infiltration increases —> surface run off decreases —> flood risk decreases/less pollutants entering river
- Permeable Pavements- pavements made out of permeable material or has small gaps in between to allow infiltration —> infiltration increases —> surface run off decreases —> flood risk decreases
- Green roofing- roofs and walls covered in vegetation —> infiltration and evapotranspiration increases —> less surface run off —> flood risk decreases/less pollutants entering river
The use of vegetation in many of these structures also provide new habitats for wildlife and increases biodiversity
river restoration in london
Problems in enfield?
One area that is restoring its rivers is Enfield, north London
- Urban surfaces are impermeable —> surface runoff increases and infiltration decreases —> increased frequency and intensity of floods —> Enfield has had regular floods e.g. in 2006, 2007 and 2008
- Rains more in urban areas —> more surface runoff from roads —> increased levels of pollutants such as oil and heavy metals in watercourses —> water pollution
Aims of restoration project in 2012?
- Reduce surface runoff from roads —> less pollutants entering river —> improved water quality
- Reduce flood risks and limit the impacts of flooding on habitats and residential areas
- Provide more habitats for wildlife and new recreational areas for residents
What was involved in the project?
- Vegetated trenches have been created around roads —> increased infiltration —> decrease surface run off —> decrease flood risk/less pollutants entering rivers
- Rain planters have been installed in schools (these collect rainwater) —> less surface run off —> decrease flood risk// also educates children e.g. impacts of littering
Who was involved in the project?
- Defra and Thames Water provided funding. In 2012, Defra granted £340 000 to the project to construct more SUDS
- Local residents - Volunteers were involved in litter picking and water quality monitoring
- Local schools - Students were involved in litter picking
Successes:
- Flood risk seems to be reduced e.g. high rainfall in December 2013 and January 2014 did not cause significant flooding in Enfield
- Biodiversity has increased e.g. number of dragonflies have increased
Failures:
- Pollution and litter is still an issue
river restoration in korea
Cheong Gye Cheon is a natural river flowing west to east through the centre of Seoul
As the city developed, the river carried wastewater from around 100,000 people —> the river was seen as a sanitation and flood risk and a highway was built over it during the 1970s
In 2003, a $281 million scheme was launched to restore the river —> highway concrete was dismantled to create a 5.8km green pedestrian corridor
Successes:
- Cheonggyecheon river has become a tourist attraction —> 18.1 million visitors by 2008 (economic)
- Removal of large numbers of cars and more pedestrianisation activity in the area —> 2.5 degrees reduction in average temperatures (environmental)
- Green pedestrian corridor —> biodiversity has increased (environmental)
- Before the restoration, residents were more than twice as likely to suffer from respiratory disease as those in other parts of the city (social)
- School children have access to a valuable educational resource (social)
Failures:
- Expensive
- The scheme gentrified the area —> more desirable place to live —> house prices increased —> forced 1000s of people to move away as they couldn’t afford increasing prices —> low income households tend to be less educated so they may neglect the environment —> pushes the problems of waste pollution to poorer places where funds may not be sufficient to effectively manage these problems
- 80,000 tonnes of waste was generated from the project —> waste is expensive and difficult to get rid of —> may be left in other areas —> moves the problem downstream from neighbouring urban areas
- Although waste generated was recycled e.g. 100% of scrap iron and steel was recycled —> not possible for LICs due to insufficient funding —> water management only achievable in HICs
urban waste
urban waste in different places?
HICs:
- HICs —> higher wealth —> more consumption —> more waste
- HICs are focused on recycling etc
- urbanisation rates: slow in HICs and population of some urban areas are falling due to counter urbanisation and low birth rates —> less consumption —> less waste
- have money to treat waste
NEEs:
- NEEs —> biggest growth of urban waste e.g. china has the fastest growth in urban waste
- urbanisation rates: urbanisation is happening fastest in NEEs —> growing population —> more consumption —> more waste
- industrialisation —> more waste
- have less money to treat waste
Facts about waste:
- The average person in the UK produces 517kg of household waste each year
- Waste is estimated to account for 5% of global greenhouse gas emission
- Globally, waste increases by about 7% each year
Impacts of increasing waste generation?
- Cost —> The cost of collecting and treating waste are high
- Collection —> Many city authorities are struggling to collect increasing quantities of urban waste. In 2012 the World Bank found that 30-60% of urban solid waste in LICs is uncollected
- Pollution —> impacts air/water quality —> impacts health —> diarrhoea and cholera
- Space —> Cities are running out of landfill space so rubbish is left in public places e.g. rivers —> contaminates water —> water pollution
London and Mumbai managing waste?
London:
- London produces enough waste every year to fill 1500 olympic sized pools
Managing waste?
- Reduce single use plastic water —> partnered with thames water to install a network of more than 100 drinking water fountains across london
- Helping businesses reduce food waste —> FoodSave have supported over 200 food organisations in London to prevent food waste
Mumbai:
- Increasing population in Mumbai produces more waste —> e.g. in the neighbourhood of Chembur, waste in open rubbish dumps are burnt —> air pollution —> impacts health —> 25% of deaths in Chembur between 2008 and 2010 were caused by respiratory problems
Managing waste?
- Clean up Mumbai campaign —> cleaning up streets and educating people about how to recycle + dispose waste to limit environmental damage
- Waste pickers —> sort though piles of waste and separate the different materials —> less rubbish ends up in landfills and more is recycled
Waste stream —> the complete flow of waste from its source through to final disposal
Sustainable waste management?
3Rs:
Reduce:
- Businesses —> encouraged to reduce the amount of packaging used
- Consumers —> plastic bag charge, buying products which do not use excessive packaging
Re-Use:
- Reusing jam jars, milk containers, soft drinks/water bottles
- The most successful example is ‘BagforLife’ (reusing plastic bags —> usually supermarkets replace and recycle them when they are broken)
Recycle:
- Recycling requires waste to be separated and categorised —> some people cannot be bothered
- Requires construction of new facilities to process waste —> construction leads to be more air pollution and more GHG/ construction can be expensive
ways to manage urban waste?
Unregulated - waste is dumped in places that aren’t official disposal sites
e.g. solid waste left on streets or untreated liquid waste entering water courses —> this can damage ecosystems e.g. animals can be harmed if they swallow or get tangled in plastic waste
Recycling - Converting waste into new products
Positives?
- Recycling reduces demand for raw materials —> resource extraction decreases —> environmental impact decreases
- Producing products from recycled products generally uses less energy than making them from scratch —> less greenhouse gases are emitted e.g. CO2
Negatives?
- Recycling requires waste to be separated and categorised —> some people cannot be bothered
- Requires construction of new facilities to process waste —> construction leads to be more air pollution and more GHG/ construction can be expensive
Recovery - Using waste for energy or direct reuse
Positives?
- reduces the amount of waste going to landfill
- waste that is burnt can be used to generate electricity (energy recovery) —> reduces use of fossil fuels
Negatives?
- burning waste can emit greenhouse gases/ release toxic chemicals into the air or water
Incineration - burning waste
- 7 licensed municipal incinerators in the UK
Positives?
- reduces the amount of waste going to landfill
- waste that is burnt can be used to generate electricity (energy recovery) —> reduces use of fossil fuels
Negatives?
- burning waste can emit greenhouse gases/ release toxic chemicals into the air or water
Burial - waste goes to landfill
Positives?
- Convenient and cheap
Negatives?
- Contamination of water supplies —> rainwater passes through waste and picks up harmful chemicals/pollutants
- Methane is released —> GHG
- Running out of space
Waste submergence - Dumping waste under water
- it’s illegal but still common in some areas
Negatives?
- Submerged waste can damage ecosystems e.g. animals can be harmed if they swallow or get tangled in plastic waste
Trade in waste - waste can be bought and sold by countries e.g. developed countries may pay developing countries to take their hazardous waste —> developing countries may not dispose of hazardous waste safely —> damage local environments e.g. water pollution
