Contemporary Urban Environments 5

The phenomenon of urban areas being warmer than rural areas is called the urban heat island effect.

Urban areas with higher air temperatures than the surrounding rural areas are called urban heat islands (UHIs). For example, London has a clearly defined UHI.

The highest temperatures are found in industrial areas and in the most densely built up areas, e.g. the CBD.

There are pockets of cool air above parks and bodies of water. These are called temperature 'sinks'.

Areas within the city with the same land use generally have the same temperature. These are called temperature 'plateaus'.

Temperature can change rapidly when land use changes. Rapid changes are referred to as temperature 'cliffs'.

There are four main causes of the UHI effect:

1. Absorption of heat by urban surfaces: concrete, brick and tarmac surfaces absorb and store heat from the sun during the day. They slowly release the heat as long wave radiaton - this is most noticeable at night, when it warms the air.

2. Air pollution: air pollution from cars and factories increases cloud cover over the city. It also creates a 'pollution dome' - a layer of pollution over the city. Both these things trap outgoing heat radiation and reflect it back to the surface

3. Heat from human activity: cars, factories, offices, central heating, air conditioning units and people themselves all release heat.

4. Less evapotranspiration: when it rains the water's quickly removed by drainage systems, so there's little surface water to evaporate. Also, there isn't much…