Climate: Urban Heat Islands


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The key features of a heat island, why it forms, the effects it causes and Atlanta as a case study

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Climate: Urban Heat Islands

  1. 1. Urban Microclimates Studying the impact of urban features on climatic variables
  2. 2. Answers <ul><li>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 </li></ul><ul><li>Microclimate - localised and generalised climatic conditions that have been altered by a physical feature </li></ul><ul><li>Climatic variables - temperature, humidity, precipitation, air quality, wind direction and speed </li></ul>
  3. 3. How does an urban area influence climate <ul><li>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 </li></ul><ul><li>People, cars, buildings (type and size) and roads, vegetation, size and quantity of water surfaces, drainage, higher density of pollutants (atmospheric) </li></ul>
  4. 4. Definition of a heat island <ul><li>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 </li></ul>
  5. 5. Climatic domes <ul><li>Used to describe the “DOME” of air over a city - the upper levels of the urban heat island </li></ul><ul><li>Contains more dust, more CO2, more pollutants, less water </li></ul><ul><li>Caused by - the man made surfaces which store and re-radiate heat later in the day </li></ul><ul><li>Most extreme example - Atlanta </li></ul><ul><li>In general a year round difference of a minimum of 3 to 5 degrees is seen </li></ul>
  6. 6. Atlanta <ul><li>Where is it? </li></ul><ul><li>Atlanta’s heat island is so intense it generates its own convectional thunderstorms </li></ul><ul><li>1997 - daytime local air temp = 27 </li></ul><ul><li>Ground surface in city = 49 </li></ul><ul><li>2 till 4 am - air = 10 to 13 degree average </li></ul><ul><li>Ground temp = 24 </li></ul>
  7. 7. Atlanta’s heat island <ul><li>Landsat images pick up over 48 degrees in car parks, yet only 32 in tree islands within those car parks - evapoT reduces temperature </li></ul><ul><li>How do we solve the problem?? </li></ul>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. 8. How does Atlanta create storms? <ul><li>As heat is trapped in the city (less wind) and the city itself emits heat, warm air rises </li></ul><ul><li>Warm air rises </li></ul><ul><li>Cumulo-nimbus form (result of convection in atm) </li></ul><ul><li>As clouds rise and cool they condense to form rain </li></ul><ul><li>Typical convectional thunderstorms (nb tropical rainforests) - intense and short lived - not always in the afternoon </li></ul>
  9. 9. Why do heat islands matter? <ul><li>The Georgia heat island costs residents $25 per year </li></ul><ul><li>More electricity is needed for air conditioning systems </li></ul><ul><li>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 </li></ul><ul><li>Lack of vegetation - normally indicates presence of other problems (increased pollution, runoff problems etc) </li></ul>
  10. 10. Solutions <ul><li>Plant trees! </li></ul><ul><li>Installing highly reflective roofing </li></ul><ul><li>Using less asphalt for pavements - brighter surfaces reflect heat </li></ul><ul><li>Air quality legislation (not as politically likely as the other options) </li></ul>
  11. 11. Lesson Work <ul><li>Page 73 in the TEXTBOOK please do questions 1 and 2 </li></ul><ul><li>These will be taken in - what you have not finished in the lesson please finish for homework </li></ul><ul><li>FULL QUESTIONS TO BE HANDED IN ON FRIDAY - REASONS FOR LATE WORK MUST BE EMAILED TO ME BY WEDNESDAY </li></ul>