eTheses Repository - University of Birmingham

A reason for the sharp increase in daytime temperatures could be the reduction in the water
availability within the urbanised grid cells, as the ‘Meadows’ land cover class is converted
to the much drier urban land cover fraction. With less moisture available to absorb the
daytime heat, the sensible heat fluxes will increase and consequently raise the daytime
temperature. Since the urban areas treated with BEP neglect latent heat fluxes (Martilli
2003), the reduction in ‘Meadows’ land cover fraction within the domain will cause the
urban area to become unrealistically dry because no vegetated surfaces are represented and
the lack of cooling through evaporation will raise daytime temperatures (Jonsson 2004). As
identified in the sensitivity tests in Chapter 4, changing the fraction of vegetation within an
urban area has the highest impact during daytime which explains the larger change in
daytime temperatures compared to night time temperatures.
DTR (K)
10.7
10.6
10.5
10.4
10.3
10.2
10.1
10
9.9
9.8
0.20 0.25 0.30 0.35 0.40 0.45 0.50
Mean urban land cover fraction
Figure 7.5: Mean DTR (K) as a function of the mean urban land cover fraction as computed by the
simulations in the EXPANSION series for the second day of simulation
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