eTheses Repository - University of Birmingham

compared to the RADIUS series for similar mean urban land cover fractions. The
simulations in the DENSITY series have a larger number of less densely urbanised grid
cells with an urban land cover fraction compared to the more compact urban area in the
RADIUS and COMBINED series. This result suggests that the existence of the extensive
suburban areas surrounding the city centre has important implications for determining
mean urban temperatures and for the management of cities and their development. For the
RADIUS series on the other hand the spatial expansion of the city from 25 km 2 to 1600
km 2 is the driving factor behind the change in the spatially average near surface potential
temperature, but this appears to have a smaller effect compared to the increase in urban
land cover fraction in the DENSITY series.
6.3.2 Effect of urban growth on the REI and effective radius
It is observed that all the model runs demonstrate an increase in the average value for the
near surface potential temperature when compared with the model simulation with rural
land use (NOURB). It is however interesting to analyse the area at night time which is
affected by a change in the near surface potential temperature greater than a threshold value
of 1 K, and to relate this to the area occupied by the city for each domain. After detailed
analysis of the horizontal slices at 10 m for each model run, a minimum change of 1 K was
considered because all the simulations showed an area affected by this change at 04:00. An
effective radius (Reff) is calculated for the RADIUS and the COMBINED series of runs
using:
Reff = A(x)
/ π
(Equation 6.5)
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