The key features of a heat island, why it forms, the effects it causes and Atlanta as a case study
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1. Urban Microclimates Studying the impact of urban features on
climatic variables
2. Answers
Urban area- area of high density buildings with urban
associated services - i.e. motorways and major roads, high rise
buildings, large and densely packed population
Microclimate- localised and generalised climatic conditions
that have been altered by a physical feature
Climatic variables- temperature, humidity, precipitation, air
quality, wind direction and speed
3. How does an urban area influence climate
ACTIVITY - 10 minutes - work in small groups and devise an
explanation of how each of the below impact on
heat/temperature/humidity/wind/precipitation - one person from each
group to explain to the class
People, cars, buildings (type and size) and roads, vegetation,
size and quantity of water surfaces, drainage, higher density of
pollutants (atmospheric)
4. Definition of a heat island
An area closely allied with a high density of building in which
we find a microclimate generally consisting of higher heat, lower
wind speed, localised changes in precipitation and lower humidity
than surrounding areas
5. Climatic domes
Used to describe the DOME of air over a city - the upper levels
of the urban heat island
Contains more dust, more CO2, more pollutants, less water
Caused by - the man made surfaces which store and re-radiate
heat later in the day
Most extreme example - Atlanta
In general a year round difference of a minimum of 3 to 5
degrees is seen
6. Atlanta
Where is it?
Atlantas heat island is so intense it generates its own
convectional thunderstorms
1997 - daytime local air temp = 27
Ground surface in city = 49
2 till 4 am - air = 10 to 13 degree average
Ground temp = 24
7. Atlantas heat island
Landsat images pick up over 48 degrees in car parks, yet only
32 in tree islands within those car parks - evapoT reduces
temperature
How do we solve the problem??
In this false colour image of Atlanta, trees and other
vegetation appear red and buildings, streets and other urban land
covers appear white or blue-green to almost black in colour. The
lighter the colour the hotter the surface 8. How does Atlanta
create storms?
As heat is trapped in the city (less wind) and the city itself
emits heat, warm air rises
Warm air rises
Cumulo-nimbus form (result of convection in atm)
As clouds rise and cool they condense to form rain
Typical convectional thunderstorms (nb tropical rainforests) -
intense and short lived - not always in the afternoon
9. Why do heat islands matter?
The Georgia heat island costs residents $25 per year
More electricity is needed for air conditioning systems
The power company must create the ability to produce extra
power when needed on the few days a year - therefore it costs more
year round
Lack of vegetation - normally indicates presence of other
problems (increased pollution, runoff problems etc)
10. Solutions
Plant trees!
Installing highly reflective roofing
Using less asphalt for pavements - brighter surfaces reflect
heat
Air quality legislation (not as politically likely as the other
options)
11. Lesson Work
Page 73 in the TEXTBOOK please do questions 1 and 2
These will be taken in - what you have not finished in the
lesson please finish for homework
FULL QUESTIONS TO BE HANDED IN ON FRIDAY - REASONS FOR LATE
WORK MUST BE EMAILED TO ME BY WEDNESDAY