eTheses Repository - University of Birmingham

UHI intensity (K)
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0
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Control run (Meadows) Sand Mixed
Time
Heath Bushes Mixed forest Coniferous forest
Figure 4.21: Diurnal variation of the UHI intensity (K) as computed by the simulations representing
different examples of rural land cover surrounding the urban area for the second day of simulation.
The UHI is predominantly a night time phenomena, and in all simulations it is less intense
during the day time. The day time peak of 1.5-2.5 K occurs at roughly the same time for all
the simulations (13:00). It is observed that the UHI peaks at a maximum value, and at the
earliest time (04:30), for the simulation with a ‘Heath’ background, and is least for the
simulation with the ‘Sand’ background. The two forest simulations (ga7 and ga8) show
very similar behaviour as far as the diurnal cycle of the UHI is considered, which is not
surprising since their surface characteristics are very similar, and in some cases identical.
The ‘Heath’ land cover class is characterised by a very low thermal conductivity compared
to the other classes, which means it will have a smaller ability to conduct heat compared to
other classes. It also has a high saturation value for water content. For the city surroundings
in the different simulations, the potential temperature over the ‘Heath’ land cover class at
04:00 is almost 2 K lower than over the mixed land cover class, whereas during daytime it
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