Climatic Change in the Micro Scale

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Climatic Change in the Micro Scale

• How built up areas modify temperatures

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Recap on previous lesson

• Last lesson (8th Feb) we looked closely at the
  impact on humans of extreme weather
• In particular you shouldve done case studies on
• Strong winds (MEDC LEDC)
• Drought (Sahel)
• Heavy rain (Mozambique)
• You also answered a mini-essay-
• People in MEDCs do not escape climatic hazards,
  but people in LEDCs suffer more
• What was this all about?

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City Climates

• We have seen how, on the Macro scale (large
  scale) climate is affected by things such as
  Latitude, Altitude, Prevailing wind, the position
  of the ITCZ etc
• However, climate can also be different on the
  Micro scale.
• A good introduction to this concept is to think
  about the local area- Sedgley is often said to
  have its own Microclimate
• i.e. when the whole of the region is
  experiencing a certain type of weather, Sedgley
  is often different e.g. Colder, or Warmer than
  expected

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Why?

• During the summer of 1992, Spain hosted 3
  special events.
• Barcelona Olympics
• Expo 92
• The Moreton Family holiday

Daily temperatures in Nerja (nr Malaga) were on
average 37c (100f)
Daily temperatures at Expo 92 in Seville exceeded
105f on many days
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Evidence from the Met Office

• A microclimate is the distinctive climate of a
  small-scale area, such as a garden, park, valley
  or part of a city. The weather variables in a
  microclimate, such as temperature, rainfall, wind
  or humidity, may be both subtly different to the
  conditions prevailing over the area as a whole
  and to those that might be reasonably expected
  under certain types of pressure or cloud cover.
  Indeed, it is the amalgam of many, slightly
  different microclimates that actually makes up
  the climate for a town, city or wood.

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Different types of microclimate

• In the UK we find distinctive Microclimates in
  the following places-
• Upland- altitude affects temperatures due to the
  Environmental lapse rate. There are also the
  presence of Anabatic (warm day), and Katabatic
  (cool night) winds which blow up and down
  valleys. Places adjacent to Upland areas can
  suffer Föhn effects, giving a rain shadow.
• Coastal- Coastal areas have land breezes and sea
  breezes that are generally mild during the winter
  months and cool in the summer. Warm onshore
  breezes can also lead to localised fog

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Different types of microclimate

• Forest- Woodland areas can be cooler and less
  windy than surrounding grassland areas, with the
  trees acting as a windbreak and the incoming
  solar radiation being 'filtered' by the leaves
  and branches. However, these differences vary
  depending on the season, i.e. whether the trees
  are in leaf, and the type of vegetation, i.e.
  deciduous or evergreen.
• Urban- These are perhaps the most complex of all
  microclimates. With over 75 of the British
  population being classed as urban, it is no
  surprise that they are also the most heavily
  studied by students of geography and meteorology.

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Why do cities have such an effect on climate?

• City growth has totally altered the natural
  landscape
• Think about how many cities there are now in the
  world that hold over 1 million people
• And then think about how many have over 10
  million. Some have over 20 million people
• How many houses is that?
• How many roads?
• How much tarmac / asphalt?
• It is these reasons that some cities make there
  own climate

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City Climates

• The table below summarises some of the
  differences in various weather elements in urban
  areas compared with rural locations

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Urban heat islands
Marked differences in air temperature are some of
the most important contrasts between urban and
rural areas shown in the table on the previous
slide. Chandler (1965) found that, under clear
skies and light winds, temperatures in central
London during the spring reached a minimum of 11
C, whereas in the suburbs they dropped to 5 C.
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What causes heat islands ?

• The release (and reflection) of heat from
  industrial and domestic buildings.
• The absorption by concrete, brick and tarmac of
  heat during the day, and its release into the
  lower atmosphere at night.
• The reflection of solar radiation by glass
  buildings and windows. The central business
  districts of some urban areas can therefore have
  quite high albedo rates.
• The emission of hygroscopic pollutants from cars
  and heavy industry - these act as condensation
  nuclei, leading to the formation of cloud and
  smog, which can trap radiation. In some cases, a
  pollution dome can also build up.
• Recent research on London's heat island has shown
  that the pollution domes can also filter incoming
  solar radiation, thereby reducing the build up of
  heat during the day. At night, the dome may trap
  some of the heat from the day, so these domes
  might be reducing the sharp differences between
  urban and rural areas.
• The relative absence of water in urban areas
  means that less energy is used for
  evapotranspiration and more is available to heat
  the lower atmosphere.
• The absence of strong winds to both disperse the
  heat and bring in cooler air from rural and
  suburban areas. Indeed, urban heat islands are
  often most clearly defined on calm summer
  evenings, often under blocking anticyclones.

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Urban Heat Island in Chester
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Task-

• Read the information about Atlanta on Page 72
• Answer questions 1 and 2 from Page 73

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Summary so far

• Urban areas have slower wind speeds in general,
  due to the tall buildings
• Sometimes the opposite can happen, with wind
  channelling down streets
• Towns and cities have more clouds and rain
• Tall buildings encourage air uplift (they become
  very hot). Hence there are many thunderstorms in
  Larger urban areas
• Air quality is poor- many pollutants cause smog
• Heats islands are more apparent in Large Urban
  areas with a greater concentration of People,
  buildings and cars

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Atmospheric Pollution in Urban Areas
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• You have been asked to make a short 5 minute
  presentation on an urban air pollution case
  study.  The key questions that you will need to
  address are
• What are the air pollutants of most concern?
• What are the primary sources of these pollutants?
  
• Are there any factors about the city that make
  air pollution more of a problem (e.g. topography)
  
• What are some of the impacts of the air
  pollution?
• What strategies are being implemented to tackle
  air pollution in the city and who by?
• What do you think the future prospects are for
  air pollution in the city in the next 5 years and
  20 years?
• There is a fair bit there, so make sure you focus
  on the questions, make the presentation punchy
  and don't dwell on too much detail.

There are 3 case studies in the Textbook (London,
Los Angeles, Mexico City), but there is a wealth
of information online. You are going to work in
pairs
Next week you will present your case study to the
class- you will need to make notes on what the
other groups say- it will help in your exams
If you want to display anything on the projector,
note that the laptop has no floppy-disc drive.
Put your presentation on CD or memory stick. If
you want anything photocopied for the group, see
me in the week
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• You have just been given a page full of weblinks.
  This can also be found on-
• http//www.geography-help.co.uk/as_level_schedule_
  2004_05.htm