9 - Urban Climate Flashcards
What is an urban heat island (UHI)?
Urban areas with higher air temperatures than the surrounding rural areas. Really clear in London!
What is the urban heat island effect (UHI effect)?
The phenomenon that urban areas are warmer than rural areas.
Where is the highest/peak temperature?
In industrial areas and in the most densely built up areas e.g the Central Business District (CBD)
What are temperature sinks?
Pockets of cool air above parks and bodies of water (e.g rivers or ponds)
What are temperature plateaus?
Areas in a city with the same land use generally have the same temperature.
What are temperature cliffs?
When temperature changes rapidly due to land use change e.g inner city housing to CBD high rise buildings!
What are the 4 main causes of the UHI effect?
The albedo effect - urban surfaces (concrete, brick and tarmac) absorb heat!
Air pollution - trap outgoing heat due to increase in cloud cover and a pollution dome.
Human activity - cars, factories, offices, central heating, air conditioning, and people themselves!
Less evapotranspiration - little surface water and plants so no evapotranspiration which means less heat energy is used up.
How does the UHI effect vary seasonally? Why?
It’s stronger in summer (in mid-latitude cities like London)
Average winter temps are 2 degrees warmer but average summer temps are 5 degrees warmer.
There’s more solar radiation in the summer, so urban areas absorb more heat then than they do in the winter.
How does the UHI effect vary diurnally (between the day and night)? Why?
It’s stronger at night.
Average day temps are 0.6 degrees warmer but average night temps are 3-4 degrees warmer.
Rural areas cool down at night but urban areas don’t because they continue to release the heat absorbed during the day.
What is an anticyclone and why is the UHI effect stronger during one?
Anticyclones cause clear skies and low winds.
If there are no clouds, more solar radiation reaches and is absorbed by urban surfaces.
Low winds mean warm air isn’t blown away.
Why is average wind speed usually lower in cities than in rural areas?
Tall buildings create friction that slows down moving air.
Some areas are totally sheltered so wind speed can be zero there.
How is turbulence caused around buildings?
Wind hits the face of the building and is deflected down, around the sides and over the top.
What are vortices and how are they created in urban areas?
Bodies of swirling air created when winds deflected from one building hits another building or the ground.
What is the canyon effect?
Wind is channelled down streets creating powerful gusts.
What are the implications of the canyon effect?
For building design and town planning, building position, the location of doorways and building size must be considered.
