eTheses Repository - University of Birmingham

(Peterson 1969; Changnon 1992; Collier 2006). These changes are often comparable to those
projected by future global and regional climate change (Baker et al. 2002). Despite covering only
1.2% of the Earth’s surface (Shepherd 2005), the UN estimated that in 2003 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). It is therefore important to
understand how these increasing urbanisation patterns might be affecting local and regional
climate, both from the point of view of human wellbeing (Jin et al. 2005), their support systems
(Baker et al. 2002), and the effect on long term temperature records. In particular controversy
exists over the influence of urban warming on large scale surface-air temperature trends (Kalnay
et al. 2003) and there are indications that some long term stations might have been affected by
urbanisation (Karl et al. 1988; Philandras et al. 1999).
Estimating the urban effect and the UHI in particular is far from easy. As seen in Section 2.1.3
urban effects manifest themselves at different scales. Obtaining representative measurements at
the city scale is not easy. One possibility is to compare data from an urban station with that from
a rural one in the surrounding area (Karaca et al. 1995; Tayanc et al. 1997; Figueroa et al. 1998;
Brazdil et al. 1999; Philandras et al. 1999; Baker et al. 2002; Jauregui 2005). However it is also
necessary to account for the effects of topography and other natural features, and to be certain
that the rural station is not influenced by the urban area (for example if it is downwind of the
city). Another possibility is to analyse the urban effect through historical analysis of the
temperature time series of stations that are considered urban due to city growth (Jones et al.
1990; Yague et al. 1996; Philandras et al. 1999), however for most areas a comprehensive set of
pre-urban measurements is not available for comparison and it is necessary to stratify station-by-
station differences before and after urbanisation according to weather type (Lowry 1998). Other
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