urban climates

• Urban areas create their own climate and weather, called microclimate (define)

  the small scale variations in temperature, precipitation, humidity, wind speed and evaporation that occurs in a particular environment
• Urban Heat Island effect statistics

  the annual mean air temperature of a city with one million or more people can be 1-3*C warmer than its surroundings. Temperatures will fluctuate dependent on season, weather conditions, sun intensity and ground cover.
• reasons for cities being warmer than rural areas

  • building materials such as concrete and brick have much lower albedo, absorbing large quantities of heat during day
  • air pollution from industries and vehicles increases cloud cover and creates a pollution dome, which absorbs a large amount of outgoing radiation and reflects this back to the surface
  • heat coming from the fuel burnt in industries, buildings and vehicles
• strategies for managing urban heat island

  • green roofs- can reduce rooftop temps by 20-40*C on a sunny day, acting as insulators
  • urban greening - provides shade and can have a natural cooling effect
• reasons for convention rainfall tending to be heavier and more frequent in urban areas

  • UHI generates convection - heated ground surfaces = rapid evapotranspiration = results in cumulus cloud
  • city pollution can increase cloud formation and rainfall
  • large amounts of water vapour produced from industrial sources and power stations
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