Notes Created By Chanelle. B
Urban Climates
Microclimate of a city:
- Temperatures, humidity and rainfall are different
Temperatures
Cities are warmer because:
- artificial materials (concrete/bricks) ---> absorb more heat
- artificial sources of heat (air conditions/ power stations/ car engines/ people)
- water is taken away in drains/ fewer plants
- High buildings have larger surface areas ---> absorbs heat
- Polluted air ---> slower cooling at night
Humidity
- Humidity of air describes amount of water vapour in air
- Cities are less humid ---> water is carried away by drains/ fewer plants
Rainfall
- Greater over cities
- Includes mist/ fog/ clouds/ dew/ frost/ rain/ snow
- Water vapour only condenses if hygroscopic nuclei exists
- Pollution promotes condensation
- Hotter air creates upward convection currents ---> thunderstorms
Hygroscopic nuclei:
Particles in air (e.g. smoke, salt, dust) that attract water vapour and provide a surface
for water vapour to condense
Urban heat islands:
- Central part of city is warmer than suburban/rural areas
- Hot air rises above centre
- Cool air moves in from rural areas ---> replaces hot air
- Heat island is dome shaped cushion of warm air ---> dominant air pressure over
region is anticyclonic ---> subsiding warm air ---> polluted air cant rise high into
atmosphere
- Heat islands are smaller at night
- City cools, hot air rising is weak, surfaces lose heat quicky
1
Urban Climates
Microclimate of a city:
- Temperatures, humidity and rainfall are different
Temperatures
Cities are warmer because:
- artificial materials (concrete/bricks) ---> absorb more heat
- artificial sources of heat (air conditions/ power stations/ car engines/ people)
- water is taken away in drains/ fewer plants
- High buildings have larger surface areas ---> absorbs heat
- Polluted air ---> slower cooling at night
Humidity
- Humidity of air describes amount of water vapour in air
- Cities are less humid ---> water is carried away by drains/ fewer plants
Rainfall
- Greater over cities
- Includes mist/ fog/ clouds/ dew/ frost/ rain/ snow
- Water vapour only condenses if hygroscopic nuclei exists
- Pollution promotes condensation
- Hotter air creates upward convection currents ---> thunderstorms
Hygroscopic nuclei:
Particles in air (e.g. smoke, salt, dust) that attract water vapour and provide a surface
for water vapour to condense
Urban heat islands:
- Central part of city is warmer than suburban/rural areas
- Hot air rises above centre
- Cool air moves in from rural areas ---> replaces hot air
- Heat island is dome shaped cushion of warm air ---> dominant air pressure over
region is anticyclonic ---> subsiding warm air ---> polluted air cant rise high into
atmosphere
- Heat islands are smaller at night
- City cools, hot air rising is weak, surfaces lose heat quicky
1
