CUE Bk4 - Urban Climate Flashcards
What happens to these elements of the climate in an urban area compared to rural areas?
1. Temp
2. Precipitation
3. Relative humidity
4. Visibility
5. Wind speed
6. Radiation (sun)
7. Pollution
- Warmer
- Incr
- Decr
- Incr
- Decr
- Lower
- Incr (1,000%)
What are the 2 zones within an urban canopy?
- below roof level
- urban boundary layer > nature of urban surface
UHIE
1. What does it stand for
2. Reasons for such a large difference in figures
3. What is the name of the effect linked to dark surfaces
4. What is the name for when different parts of the city are at different temps
- Urban heat island effect
- more heating on
- building materials retain heat
- lower wind speeds
- dark coloured surfaces
- pollution
- more enclosed areas
- vehicles
- heat sources
- Albedo effect
- Isotherms
Issues linked to high summer temps
- incr evapotranspiration + rainfall
- more energy having to be produced for air conditioning
- incr unreliable weather
- incr crop failure
- drought
- wildfires
- heat exhaustion/heat stroke
- melting ice
- loss of industry (farming)
- health issues > skin conditions, respiratory issues
- midday peak and lack of night cooling
- incr pests and disease > new food sources
- changing tourism habits
- water shortages + water quality issues
- surge in energy demand
- tropical diseases
UHIE is the product of a number of factors (8)
- anthropogenic heat sources
- multiple reflections > incoming radiation from tall buildings
- surfaces have a lower albedo
- efficient drainage > decr availability for evaporation
- lower amounts of vegetation > transpiration
- dome of particulate and NO2 pollution > allows shortwave radiation
- incr cloud cover
- incr roughness > decr wind speed
When is the largest contrast in the UHIE
+ what does diurnal mean
- calm high pressure
- temperature inversion
- most distinct in winter
- most distinct at night
Diurnal > changes within the day
What are examples of micro hot spots and micro cold spots in cities?
Hot spots
- large car parks,shopping centres, industrial units
Cold spots
- parks, fields, water bodies
Methods of dealing with UHIE?
- incr surface reflectivity (incr albedo) white surfaces
- incr vegetation e.g. green roofs > incr evapotranspiration + reduce CO2, act as insulator, incr biodiversity, attractive, decr surface runoff
- urban greening > planting trees on east + west
- place air conditioning units in the shade
- cool cars > white
What is the reason for the high heat risk in London?
Excessive urban heat island effect
What is the urban heat island effect?
Large cities have higher temperatures than the surrounding areas because of a variety of human activity. Dark surfaces absorb heat during the day and mass heating causes warming.
When is the UHIE most likely to occur?
On a calm night during an anticyclone when there is less mixing of air. The high pressure leads to cloudless skies. By contrast rural areas tend to have lower temperatures.
What are the 3 changes to precipitation and fog due to it being in an urban area instead of rural?
- Incr in rainfall
- Reduced amounts and incidents of snowfall
- Lower relative humidity
In urban areas compared to rural areas, what is the percentage increase in precipitation?
10%
Why is there increased rainfall in urban areas?
- rainfall a result of low pressure
- albedo effect occurs due to more dark surfaces
- warmer surfaces warm up surrounding air
- rising air
- depressions and updrafts
- more intense thunderstorms
- major cities located at water sources so there is a source of moisture + availability for evaporation
What do dust particles act as when they combine with a water droplet magnet, which is linked to pollution?
Hydroscopic Nuclei
What is the reason for why relative humidity is lower overall in urban areas but not at night?
- fewer water bodies, vegetation + more efficient run off
- urban maintains humidity at night as in rural areas air cools rapidly + moisture decr due to dew fall
What is the reasoning (2 components) that cause fog to occur more regularly in urban areas?
- Decr relative humidity
- Pollution levels
List the facts and figures below about London
1. Number of days a year in early 1700s with smog
2. Number of days a year in late 1800s with smog
3. Incident that caused 12,000 deaths in 4 days
4. When clean air act was created
- 20
- 50
- The Great Smog of late November/early December 1952 > real ‘pea-souper’
- 1956
What does the NEE’s term ‘apocalypse’ mean?
Used to describe the high death toll which is created when fog traps pollutants to create toxic smog
In urban areas
1. Annual mean speeds are…
2. The frequency of claims can be…
- 20-30% lower
- 5-10% higher
What is the Venturi effect?
+ what is done to try and counteract this
- when the pressure in the gap between 2 buildings causes the wind to pickup speed and reach high velocities
- some buildings are put on stilts to avoid this but some wind flow is needed to remove pollution
- Buildings are in groups and their size and spacing can alter wind patterns
Examples of buildings that have been adapted to cope with winds in urban areas
- Burj Kalifa, Dubai
- over 828m
- tallest building in the world
- concern over vortexes pulling the building side to side
- softened edges to wind can go by
- sways 2m side to side
What effects do urban buildings have on wind?
Urban buildings produce a lot of friction, which slows down the wind and alters its direction. However, winds are channeled down long straight streets where there is less friction. These are called urban canyons.
Facts and figures relating to how urban air quality is poorer than rural areas.
X what changes in..
1. Carbon monoxide
2. Carbon dioxide
3. Nitrous oxide
4. Sulphur oxide
- General increase
- X2
- X10
- X200
