Luke Howard first demonstrated London’s heat island in 1818. He compared temperature readings from 1806 at Somerset House (off the Strand) with readings from various sites in open country beyond the city. Since then, many studies have documented the fact that temperatures in cities tend to be higher than in surrounding rural areas. This is most evident at night, especially when it is cloud-free and calm. Urban heat islands have been demonstrated all over the world, from Singapore to Fairbanks, Alaska.
The urban heat island results from changes in the energy balance, partly because of the replacement of vegetation by concrete, brick and tarmac, and partly because the urban surface morphology is more complex than rural surfaces. To understand the urban heat island for any settlement, it is necessary to analyse the changing energy balance of the city compared to its surrounding area. Usually, the comparison is made for both day and night in order to show how differences in the daytime heat balance generate significant contrasts in temperature at night.
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