eTheses Repository - University of Birmingham

characterised by appropriate values of the roughness length, albedo, evaporation, heat capacity
and thermal conductivity. It was found that the hypothetical urbanisation scenarios (increase in
densely urbanised area of 12.5% and 37.5%) did not cause a significant modification of the local
winds over the Greater Zagreb area. In the urbanised areas and their vicinity reductions in the
average wind speed were found, but no significant change in wind direction was documented.
Mölders and Olsen (2004) performed simulations to investigate the impact of urban growth (the
town area is enlarged by 20%) on precipitation for a high latitude city, but as in previous studies
the city was represented by appropriate values of the albedo, emissivity, roughness length and
stomatal resistance, and by a change in the empirical values used to calculate transpiration.
All the above literature examples consisted of short term simulations, generally 48-72 hours
long, for typical summertime conditions and investigated physical processes involved in the UHI
formation and related effects. This is the approach that will be followed in this PhD study as
well. A small number of other studies have conducted longer simulations, for example Lamptey
et al. (2005) performed 5 year simulations for the North-Eastern United States to examine the
presence of the urban areas on climate. However, the focus of Lamptey et al. was on the long
term climate and therefore the results were averaged monthly or seasonally in order to smooth
out differences in urban effects for different days, for example the increase in intensity of the
urban heat island for calm, clear nights. Also the large spatial resolution (36 km) adopted means
that different land use zones within cities were ignored, which might have influenced the results.
Lamptey et al. found an increase in near surface temperatures of more than 1 K over urban sites,
in both summer and winter, as a result of urbanisation, and a decrease in the diurnal temperature
range of 0.4 K due to the same cause.
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