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