eTheses Repository - University of Birmingham

The REI showed that for all the variables considered there is an effect which extends
beyond the area directly classified as urban, and that this extent is much greater during
night time than during daytime, when urban effects due to the release of daytime heat
stored within the building materials are large.
It is hard to simulate the precise evolution of the urban area, since detailed and
comprehensive maps showing the change of urban land cover with time are not readily
available in a format which can be assimilated by the METRAS+BEP model. An attempt
has therefore made to understand the key determinants of the change in near surface
temperature and wind speed by using the mesoscale model as a numerical laboratory, rather
than a forecast tool (as suggested in Tjernstorm et al. 2000). The land cover in the scenario
domains was constructed from the current London land cover, and assumptions based on
the literature and possible forms of urban development.
The results of the scenarios show a higher mean potential temperature for both daytime and
night time, and a lower wind speed, for an urban area of the current size of London but with
increased vegetation fraction (DENSITY series), when compared to a smaller urban area
but with higher urban land cover densities (RADIUS series). The change in the ratio of the
effective radius and the urban radius shows only a very small variation as the city size
increases. These results show that the extensive urban growth, and in particular the
reduction in vegetation within the London urban area, has affected near surface
temperature, wind speed and the UHI. The extent of these changes largely coincides with
the area of increasing urbanisation, although the REI also shows that the effect is present in
the rural areas surrounding the city. The dangers of removing green cover in urban areas
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