This note pack is a complete summary with diagrams. It summarises all the content for Topic 2 : Climate and Weather Introduction. Chapter 5 : Urban Climates in the Focus Geography Grade 12 Learner's Book.
Subtropical anticyclones and associated weather conditions Geography 12 IEB
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Urban Climates
Differences between Rural & Urban Climates
● Temperature, humidity & rainfall in city different from rural area
● City different microclimate to rural
● City warmer than rural
Reasons for temperature variations
● Cities - many artificial sources of heat
○ Eg. air conditioning, power stations, car engines, domestic & industrial heating
● Cities built artificial substances - absorb more heat than soil & grass
○ Eg. concrete, glass, bricks & tar
● Urban areas, water taken away in drains & not many plants
● Rural areas large amount heat used in evaporation from water sources & transpiration from
plants
● High-rise buildings large surface areas
○ Sun strikes side buildings in morning, heat absorbed
● Cities polluted air
○ Causes city cool down more slowly at night
○ Polluted area acts like blanket, trapping warm air close to city in evening
Humidity & Precipitation in Cities
Humidity of air describes how much water vapour there is in the air
Usually, the air is less humid in cities than air in rural areas
● Water in cities carried away by stormwater drains
● Fewer plants in urban areas - less water vapour being added to air through transpiration
● Water vapour in air condenses only if there are hygroscopic nuclei
○ Particles in air such as dust, salt & smoke
○ Attracts water vapour & provide surface for water vapour to condense
○ Pollutions consists of smoke & dust
○ Pollution provides hygroscopic nuclei = increase amount of condensation
● Thunderstorms more frequent over cities - hotter air results stronger upward convection
currents
, Climate factor Rural Area Urban Area
Temperature Cooler - fewer artificial Warmer - lack vegetation cover &
surfaces & more more artificial levels
vegetation cover
More artificial heating
More dust - prevents heat from
escaping
Pollution Less pollution & dust More pollution & dust - industrial
particles activities, combustion processes &
traffic
Cloud Coverage Fewer clouds More clouds - more dust & pollutant
particles in atmosphere
Particles = hygroscopic nuclei /
condensation nuclei
Precipitation Less rain & hail, may get More rain & hail - more hygroscopic
more snow nuclei
Relative humidity Higher relative humidity Lower relative humidity - lack
due to water retention in vegetation & natural levels
soil & vegetation
Warmer air hold more moisture, lack
of evaporation due to little
vegetation & many artificial surfaces
Wind Speed Higher Less - buildings serve as
windbreaks
Fog Visibility Less fog = better visibility More fog & poorer visibility due to
more condensation nuclei in
atmosphere
Fog problem in winter when
inversion causes pollutants to form
near the surface of the earth
Thunderstorms Less often More frequently across urban areas
Warmer air causes stronger,
upward convection & therefore
more
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