Urban Microclimates (AQA A Level Geography)

Cities create their own microclimate domes and have unique:

• Temperature ranges

• Wind patterns

• Clouds and precipitation rates

• Pollution

Urban microclimates vary according to urban areas’ size, shape and location

There are a number of causes, some of which are:

• Changes to land surface; concrete, brick and tarmac

• Cities have fewer trees than surrounding rural areas. Trees shade the ground, preventing heat from the Sun being absorbed 

• Dark rooftops and dark pavement absorb more solar radiation 

• Tall buildings reflect and absorb sunlight  

• Cars engines and factory exhaust produce heat

• Fewer plants in urban settings mean that less evapo-transpiration occurs, a process that cools the air

• Poor building insulation means release of heat at night

Within these microclimate domes, there are two levels:

• Urban canopy - processes act in the spaces between buildings below roof level

• Urban boundary - processes acting above roof level and extends downwind as a plume into the surrounding rural areas

Patterns of precipitation and air quality are extended to immediate areas via the prevailing winds

Urban climates show the following characteristics:

• 2-3 weeks fewer frosts

• Pollution levels are higher

• Fog and photochemical smog is likely

• 5-15% more precipitation 

• Lower relative humidity

• 5-10% more cloud

• Increased thunderstorms

• Lower wind speeds, with exception of tunnelling effect

• Pressure gradients

• Greater diurnal temperature range - higher max and min temperatures as compared to rural areas