URBAN MICROCLIMATES - THE HEAT ISLAND EFFECT
During the late 19th century, it was suggested that towns and cities had their own climatic features
which were distinctively different from those found in surrounding rural areas. For example, London
at the turn of the century had many "pea-soup" fogs during the winter months, whilst some people
suggested that rain in the Lancashire milltowns was triggered by pollution from the factories.
Studies undertaken after the Second World War have confirmed these suggestions, and in 1965, T.J.
Chandler undertook a number of surveys across London to analyse in more detail these subtle
differences in temperature. He found that temperatures in Central London during mid-May were
up to 6 degrees higher than in the rural suburbs, and also that these differences were most
noticeable under calm, still conditions. Similar work in the U.S.A. has also noted similar
temperatures differences between rural and urban areas, and these surveys have led to the
notion of an urban heat island.
Click here to see the results of Chandler`s survey and London`s
"heat island".
A number of factors contribute to this heat island effect:
Darker surfaces absorb heat during the day and conduct it back into the atmosphere.
Multistorey buildings and tower blocks reflect light from glass windows, and conduct heat into
the lower atmosphere from heating systems and air conditioning units.
Less heat is lost through evapo-transpiration compared with the countryside.
Heat is produced by human activity e.g. industry.
Click here for information on other changes to the microclimate caused
by urban areas.
Written by Dr.A.K.Hignell - Head of Geography at Wells Cathedral School.