eTheses Repository - University of Birmingham

Chapter 1: Introduction
Urban areas are one of the most obvious examples of human modification of the Earth’s surface.
Despite covering only 1.2% of the Earth’s surface (Lamptey et al. 2005; Shepherd 2005), it is
estimated that in 2003 about 48% of the World’s population resided in urban settlements (UN
2004). By 2030 it is expected that 61% of the World’s population will be living in urban areas
(UN 2004). Urbanisation is an extreme example of human land use modification, since it
radically alters the physical properties of the Earth’s surface and may also affect the thermal,
radiative and aerodynamic character of the surface (Oke 1987). Since such a high proportion of
the World’s population reside in urban areas it is important to understand the processes
determining urban climates, and how both past and future urbanisation patterns might affect
climate at the local and regional scale.
Urban areas have well documented effects on the environment, such as changes to the local
winds and turbulence (Roth 2000), changes in cloud cover and precipitation (Changnon 1992)
and the urban heat island phenomenon, i.e. the increased temperature of the urban surface
compared to its rural surroundings (Oke 1981). All these effects result from mechanical and
thermal modifications induced by the urban surface. The most important modifications to the
surface energy balance in urban areas consist in the moisture availability controlling the
partitioning into sensible and latent heat fluxes, the street geometry and surface radiative
properties affecting the radiation balance and the thermal properties of the building materials
causing the heat storage in the city to be significantly larger than in surrounding areas (Oke
1982).
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