CUE - Urban Climate Flashcards
What is the urban climatic dome?
The urban area within which the climate and weather is different from that of the surrounding rural areas in terms of temperature, relative humidity, precipitation, visibility, air quality and wind speed.
Urban weather has less…
sunshine duration occurrence of frosts relative humidity in winter relative humidity in summer snowy days
Urban weather has more
total precipitation rainy days annual mean temp winter max temp cloud cover occurrence of fog condensation nuclei
What is the urban canopy?
The urban canopy is the layer of air closest to the surface in the cities, extending upwards to mean building height, where processes act in the spaces between buildings.
What is the urban boundary layer?
The layer above the urban canopy, that forms a dome of warmer air that extends downwind and, at height, as a plume into surrounding rural areas.
How do urban surfaces have different albedos than rural areas?
In urban areas there are more dark surfaces such as pavements and roofs, which have a very low albedo. In addition, there are many highly reflective buildings made from glass which have very high albedos but reflect the heat back onto the ground and into the city.
4 reasons why temperatures fluctuate in urban areas
season
weather conditions
sun intensity
ground cover
4 causes of the urban heat island
albedo - building materials have low albedo so absorb heat in day and release at night, large windows concentrate heating effect into surrounding streets by reflecting energy downwards
air pollution - industries and vehicles, increases cloud cover and creates pollution dome
urban moisture and heat budget - water falling on surface disposed of asap, reducing evapotranspiration, more energy can heat atmosphere
industry and people - industries, buildings vehicles burn fuel. air conditioning units release hot air to atmosphere. people generate heat
Issue with the urban heat island: as temperatures rise in the summer months…
Conditions in buildings and on city transport systems can become uncomfortable. Increases cases of heat stroke, asthma, organ damage and death. Babies and elderly are most likely to be affected.
Issue with the urban heat island: Hot and still anticyclonic weather conditions responsible for intensive urban heat island events…
Also produce higher air pollution levels.
Issue with the urban heat island: prolonged survival and high reproduction rates of…
Some animal and insect pests can be a problem. There is greater potential of algal blooms in water courses.
Issue with the urban heat island: earlier flowering times of…
plants and trees in cities and a prolonged growing season may cause discomfort for city residents due to a longer allergy season.
Issue with the urban heat island: increased water consumption…
by residents and businesses places extra strain on the water supply infrastructure and can lead to water use restrictions.
Issue with the urban heat island: excessive heat puts…
an increased strain on the supply of energy for cooling and air conditioning.
Issue with the urban heat island: climate change…
is expected to increase the intensity of the urban heat island effect in most urban areas.
Issue with the urban heat island: an increased risk of the deterioration…
of historical monuments and buildings through increased rates of temperature related chemical weathering.
Strategies to address the issues with the urban heat island: cool surfaces
roofs built from materials with high albedo absorb and store less solar energy during the day, so emit less heat at night.
Strategies to address the issues with the urban heat island: green roofs
reduce rooftop temperatures by up to 20-40 degrees. reduce rainwater runoff, act as insulators and increase urban biodiversity.
Strategies to address the issues with the urban heat island: urban greening
planting trees and vegetation provides shade and can have a natural cooling effect. they also act as carbon stores, can reduce urban flooding and filter pollutants from the air.
Strategies to address the issues with the urban heat island: sky view factor
the openness between buildings in an urban area. a restricted sky view reduces the escape of heat from street and building surfaces, contributing to heat within street canyons.
Strategies to address the issues with the urban heat island: cool cars
a lighter coloured car reflects more sunlight than a traditional dark car. this cools the inside of the car and reduced the need for air conditioning.
Causes of photochemical smog
2 main causes are vehicles and industry
- most likely in anticyclonic conditions: high pressure system, dry, little wind or cloud
- also when temperature inversions occur (cold air trapped under warm): e.g in LA (where there’s a basin)
- pollutants are trapped
- sunlight reacts with pollutants (e.g nitrogen oxides)
Where does carbon monoxide mainly come from?
road transport
What causes nitrogen dioxide?
road transport (50%)
Where do particulates mainly come from?
Power stations and vehicle exhausts
Source of sulphur dioxide
industry e.g power stations
Impact of carbon monoxide
affects the transport of oxygen around the body
breathing in low levels can result in: headaches, fatigue, nausea
Impact of nitrogen dioxide
can inflame the lining of the lung - worse for people who suffer from asthma
oxidation of this can also cause weathering of buildings
Impact of particulates
health problems for the airway and lungs
Impact of sulphur dioxide
coughing tightening of chest and narrowing of airways
can also produce haze, acid rain, damage to plants and buildings
