3.2.3.4 - Urban Climate Flashcards
What aspect of the climate can urban areas modify?
Windspeeds
Temperature
Clouds of precipitation.
Pollution.
In what ways can winds be modified by urban areas?
Lower speeds
Greater variability.
Large-scale convection.
Why are windspeeds generally lower in urban areas?
The roughness of the land surface, consisting of buildings, at a variety of heights, create greater surface friction
What is an urban canyon?
A street with tall buildings, either side, but a space in between
What is the Venturi effect?
The effective squeezing the airflow, increased as buildings, get taller towards the city centre
Where is the highest air pressure?
In the upper part of the building with air flowing down the front and over the top
How does convection occur over urban areas?
Convection and uplift over the area means that air pressure is lowered and air is drawn in from surrounding rural areas
What is the urban heat island?
Urban areas are an average 2° warmer than the surrounding rural areas
What is albedo?
the ability of a surface to reflect sunlight. Light-colored surfaces (high albedo) reflect more sunlight than dark-colored surfaces (low albedo).
What is Skyview factor?
The amount of sky you can see without your view being impeded by Toe buildings
What is specific heat capacity?
The amount of energy required to raise the temperature of 1 kg of the material by 1 kelvin
What is the intensity of an urban heat island?
The maximum difference between the temperature of the ruralarea and the peak urban temperature
How can weather conditions impact the intensity of the urban heat island?
High pressure systems with clear nights and sunny days increase the intensity
What are the five main factors causing having heat island?
Anthropogenic heat
Height in arrangement of buildings.
Nature of building materials.
Presence of water.
Pollutants.
What is sensible heat?
Heat energy, which can be felt, as opposed to latent heat, which must be measured
How does cloud cover differ in urban areas?
It is greater
Why is cloud cover greater in urban areas?
There is more condensation nuclei, so cloud formation is greater
Why are there more thunderstorms in cities?
Enhance convectional uplift from the heat island can lead to instability in thermals, creating more storms
How do precipitation levels differ in urban areas?
They are higher
What is the speed effects?
Wind is slowed by friction from the building, friction with obstacles
What is the downdraught effects?
Turbulence is created around the top of the building, downdraught falls at the front
What is downwind eddy?
The circular motion of wind behind the building and turbulence near the top of the building occurs as the wind is forced upwards
What comes photochemical pollution lead to?
Smog – consisting of ozone and peroxyacetyl nitrate (PAN)
When will London’s ‘Pea Soupers’?
December, 1952
How did the smog form in London?
Windless, cold climate, and an anti-cyclone (little wind, high-pressure, still air) nothing moved, and the particulates were trapped
What did the smog cause?
Pneumonia, TB, heart, failure, bronchitis
How many died in the London smog?
4000+
When was the clean air act introduced?
1956
What is urban greening?
Involves growing plants wherever possible in urban areas
What are the benefits of urban greening?
– Improved air cooling, making towns and cities more bearable.
– improving air quality by absorbing gases such as CO2.
– improve respiratory health.
What is zoning of industry?
The process of dividing lands into zones, and moving industry to the outskirts
What does zoning of industry lead to?
Less particular to being trapped over the city in the cool, moist air above
What are transport solutions?
Bus only lanes introduced to encourage the use of public transport in cities, congestion charges introduced
