Urban Microclimate Flashcards
What is the urban heat island effect?
Is when urban areas have higher temperatures than rural areas
What is albedo?
The reflectiveness of a surface. The lighter the colour, the more reflective of heat/light. The darker, the more absorbent
What is the thermal gradient?
The change in temperature from CBD out towards the suburbs and rural areas
Why do towns/cities have a lower albedo than rural areas?
As there is more concrete/roads which absorb the light rather than reflect it
Why do schools in the countryside have more snow days?
As there is more green spaces/grass which reflects any heat rather than absorbs it, making snow slower to melt
What are some negatives of urban heat island?
- health issues e.g. Asthema
- hard to sleep at night
- people might faint
- old people find it harder to regulate their body temperature
- weathering (walls crumble)
- have to turn up aircon in the car which uses up more fuel
- crops struggle/seasons get messed up
- wildfires
How can the urban heat island be reduced?
- plant trees
- rooftop gardens (plants/flowerbeds)
- paint roofs white
- have allotments
What problems does air pollution cause?
- headaches
- worsens asthma
- eye irritation
- acid rain
- low visibility
- respiratory issues
- contributes to global warming/enhances greenhouse effect
What is fog?
A thick cloud of tiny water droplets in the air near the ground
What is smog?
A mixture of fog and smoke from burning fossil fuels
What is photochemical?
When pollution comes from cars (rather than factories), the smog mixes with sunlight and creates other harmful chemicals
What happened in London,1952?
12,000 people died from the smog, directly or indirectly, from either road accidents (low visibility), or asthma attacks
LOS ANGELES: dense,cool air descends and settles on valley floor + air pollution lingers over city
A) Why does smog hand over LA and not just blow away?
B) why does the sunny weather in LA make the smog worse?
A) as its in a valley so the smog would have to rise up quite considerably to not lie over buildings
B) as hot air traps the cold air, and the sun causes worse chemical reactions (turns into photochemical smog)
Where did Ella live that caused air pollution to lead to her death?
- lived 25 metres away from the south circular road in south east London
Which gas triggered Ellas asthma?
Nitrogen dioxide (levels exceeded the world health organisation and European Union guidelines)
How did the air pollution gradually affect Ella?
- was taken to hospital after a coughing fit in 2010
- placed in a medically induced coma for three days
- summer 2012 she was classified as disabled (mother had to carry her everywhere)
- died in 2013 after an asthma attack
Why do poorer people suffer more than rich people when it comes to air quality?
- poorer people can’t afford to move to the cleaner areas e.g. the suburbs (which have more green land and less cars), they will instead live near main roads which expose them to high levels of toxic gases
Why might it be helpful in the future that Ella’s death was classed as “air pollution”
- the government will start to take it seriously and try and stop further issues with health caused by pollution
What was the scheme that was set up in London to reduce air pollution?
When was it set up?
- ULEZ (ultra low emission zones)
- April 8th 2019
What are the limits to cars (if they exceed tax needs to be paid)
Motorbikes - pre 2007
Petrol cars and vans - pre 2006
Diesel cars and vans - pre 2015
What are the benefits of the ULEZ scheme?
- TFL estimated that the initial scheme will lead to reduction in toxic emissions from road transport by around 45% in 2 years
What are some negatives of the scheme?
Some drivers have spoken about their anger “really unfair”, local businesses that cant afford new vehicles
What did the gov try to do in Mexico City?
Banned cars on a Saturday, hoping to reduce pollution. Restrictions were introduced with drivers prevented from using their cars on one day per week. This system was based on number plates e.g. licence ending in 5 couldn’t drive on a Monday
What effect is traffic having on people in Mexico City?
There is toxic blanket of dirty air over the city saw thousands of people hospitalised every year
When did the scheme in Mexico City start, and what was it called?
1989, “hoy no circula”
What were some of the reasons why the scheme didn’t work?
“ the thinking was that it was supposed to get people to take public transport but they didn’t, instead, on the days they couldn’t drive they got a family member to drive them instead, or took a taxi
What will Mexico city and other cities try to do in the future?
Other cities e.g. Madrid, Paris and Athens have promised to stop the use of all diesel powered cars and trucks from the middle of the next decade. Similarly, in many cities in emerging economies they are now putting driving restrictions similar to those in Mexico in place
What are people in LIC more vulnerable to?
Food shortages
What do people in HIC’s suffer from?
Air pollution as they usually have a denser populated area. Can lead to health issues e.g. asthma
When was the warmest day in the UK?
In July 2022
What is the link between how deprived an area is and its temperature?
Data suggests people in deprived areas are more than twice as likely to live in places which are significantly hotter than neighbouring places. This is because the houses are more cramped together, and surfaces are darker (more concrete)
How is the temperature effecting Jorda’s health and life?
- the heat is very challenging
- she is frequently hospitalised with asthma attacks that leave her gasping for breath, and her symptoms are made worse by hot weather
- had to give up her job as a hair stylist
Explain heat hazard scores?
The higher the heat hazard score, the more likely it is that your area will experience high temperatures during hot weather, compared with other areas in your neighbourhood.
- a score of 1 means the postcode was in the lowest 40% of area
- a score of 5 means that the postcode was in the highest 1%
How can we fight the urban heat island effect?
- plant more trees
- green roofs and green walls can reduce the amount of heat absorbed by buildings
- use less glass
- make buildings with lighter coloured material
What are some key features of the London congestion charge scheme (2003)?
15 pounds per day
Raises money for council
Locals get a discount
Delivery vehicles to businesses have to pay
Applies in day time in ‘peak’ busy times
Electric cars discount
999 vehicles don’t pay
What are some positives to the congestion charge scheme?
- reduces pollution and encourages people to walk or take public transport
- fair to all vehicles (not excluding certain types of car depending on how old they are - like the ULEZ scheme)
- emergency service vehicles don’t need to pay which is respectful
- 90% discount for locals meaning they wont be forced to move house as the cost is too high
- reduced traffic volumes and the speed of traffic in central London, leading to reduction in air pollution e.g. NOX
What are negatives of the London congestion charge scheme?
- delivery vehicles has to pay to deliver in some areas which means they may loose out on business if people don’t want to pay extra charge
- disrupts the CBD
What is an urban wind canyon?
When there are narrow streets that have tall buildings either side, so it concentrates the wind
What is the Venturi effect?
A violent gust of wind formed in a narrow gap. The air rushes in to a low pressure area, creating a vortex (swirling wind) on the ‘Lee side’ (sheltered side) of the building
Why are wind speeds more steady in rural areas?
Because in rural areas there is nothing blocking the winds path or redirecting it
What could town planers do to reduce the concentrated wind?
Put trees in between buildings or varying building heights/space between them
How is lightening created?
Urban areas have a high density of power stations, factories and vehicles. The buildings radiate heat and give out pollution. The hot air and pollution particles rise during the day. The air cools, condense around the nuclei in clouds by afternoon and evening. The rapid rise in warm air then the rapid fall of cool air create friction. Lightening/thunder happen
Why do urban areas have more precipitation?
- fewer trees in the city than in the countryside, so less evaporation and water vapour in the air
- water vapour in the air meets tiny dust particles, the vapour turns into a liquid. This is condensation and makes rain
- cities have lots of dust particles in the air, due to high numbers of factories, cars and other pollutants
What is cloud condensation nuclei?
Particles in air that help make clouds
What is dew point?
When water vapour reaches a certain temperature and it condenses into rain
What is interception?
When rain drops lands on leaves
What is an impermeable surface?
When the ground water does not allow water to soak in e.g. tarmac/concrete
What is surface run off?
When water flows over land and does not soak in
What is infiltrated?
When water soaks down in to the layers of soil and rock
Why does the flood risk increase in urban areas?
- less evaporation occurs because there is less soil/greenery
- less infiltration (only 5% gets deeply infiltrated in central urban areas)
- impermeable surfaces
In the water cycle, what are the 4 stages?
Input e.g. precipitation on land, ice, snow
Output e.g. evaporation from ocean
Flows e.g. subsurface flows, groundwater flow, surface outflow
Stores e.g. ocean, lake, groundwater
What are the factors that cause flooding?
Precipitation
Impermeable surfaces e.g. tarmac
Agriculture (ploughed fields creates a route for water to run down in)
Deforestation
Steep hills
Poor drainage
Saturated soil
What is hard engineering in terms of drainage?
Ways to manage water drainage by building structures to control the flow of water. They can be costly and require maintenance
What is soft engineering in terms of drainage?
Ways to manage water drainage by adapting to the natural processes. They tend to be more affordable and sustainable in the long term
What are some examples of soft engineering? (Water)
- afforestation (planting trees to establish woodland or a forest). Trees increase interception and reduce through flow and surface runoff because they take up water to grow
- floodplain zoning (restricts different land uses to certain locations on the floodplain). Natural floodplains act as a natural soak away, reducing surface runoff into the channel
- river bank conservation (planting trees and bushes)
What are some examples of hard engineering? (Water)
- river straightening (cutting through meanders to create a straight channel)
- river channelisation (lining straightened channels with concrete)
- diversion splitways (flood relief channels)
What are SUDS?
(Sustainable development systems) - use natural processes to reduce flooding, and provide something for the community that improves the look of that area. They sometimes mix hard and soft engineering
What has building SUDS done to the impact of rainfall?
Flooding has decreased a lot, flash flooding has become more gradual, so build us isnt so fast
What are rain gardens? + and -
Small depressions in the ground that can act as infiltration points for water, usually running from roofs and gutters. Outside peoples homes. Gutters are often redirected to flow into rain gardens
+ small, don’t require a lot of land
+ attractive features that help improve look of environment
- not suitable for areas with steep slopes
- small, their impact is stopping flooding can be minimal
What are Swales? + and -
Swales are shallow, broad and vegetated channels designed to store and convey runoff and remove pollutants. They can be designed to promote infiltration where soil and groundwater conditions allow
+ easy to incorporate into the environment
+ easy to maintain at a low cost
- cause blockages in underground pipe work
What are permeable surfaces? + and -
Allows water to infiltrate across the entire surface by having lots of small holes on the surface. Suitable for pedestrian and vehicular traffic, and allowing rainwater to infiltrate through the surface and into underlying layers
+ can be used in high density housing developments
+ do not spoil the look of areas
- reduces effects of water pollution
- cant be used where people drive more than 30 mph
What are bioretention areas? + and -
Shallow landscaped depressions which have vegetation and filtration to remove pollution and reduce runoff downstream
+ plants removing urban air pollutants
+ easily built in new or old housing areas
- can get clogged up with weeds or litter
What is a “sponge city”
Designed to absorb rainwater to mitigate flooding by using green spaces like parks and wetlands and blue spaces like ponds and rivers to lower the amount of excess rainwater entering the sewerage system. The idea is that this prevents the need to remove water with large scale infrastructure such as sewage pipes
Is London a “sponge city”?
It’s difficult to quantify. London has an array of green spaces and there are an estimated 8.4 billion trees in the capital which help its sponginess, but its also heavily urbanised with tarmac and concrete
What is the argument against SUDS?
- require money to build
- take up valuable space for parking
- rely on regular maintenance, which will mean local doing the necessary work
- London is heavily built up so creating new green spaces is not easy, and retrofitting will sometimes prove unpopular
