eTheses Repository - University of Birmingham

the COMBINED series, for which the mean urban land cover fractions for the domains are
much smaller than in the RADIUS series. This confirms the results for the spatially
averaged temperature in suggesting that the urban land cover density is an important
determinant of the area which shows an increase in the night time potential temperature of
more than 1 K.
Analysing the model runs using the effective radius does have some limitations. Firstly, it
is not possible for example to compare an effective radius with the size of the urban area
for the DENSITY series, and secondly, defining a threshold of 1 K is not applicable for the
daytime results where the change is much smaller. The split between rural and urban grid
cells affected by the 1 K change is also neglected. Therefore a second measure, the REI, is
used to understand whether the regional effect of the urban area increases with the radial
growth and the increase in urban land cover fraction. This will lead to an understanding of
how much of the rural area surrounding the city is affected by the growth of the city.
The REI is calculated for each model run of the three series, for the domain averaged near
surface potential temperature at 04:00 and at 12:00. The results are presented in Table 6.8.
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