eTheses Repository - University of Birmingham

scheme, and therefore it was necessary to implement one into a mesoscale model. The urban
canopy scheme BEP, developed by Martilli et al. (2002) was chosen, since it has the advantage
of being a validated multi-layer canopy scheme which incorporates the influence of surface
morphology and spreads the influence of the urban surface in the vertical.
METRAS (Schlünzen 1988) is a mesoscale model which has been used to study the effects of the
urban surface on air quality. Although this model has been used to simulate the dominant effects
of the urban surface, it has a simple parameterisation of the urban surface based on the roughness
length approach. The urban surface is simulated in the same way as other land use types by using
appropriate values of surface parameters such as the albedo, roughness length. This method
neglects many of the urban canopy layer and boundary layer effects which are parameterised by
more sophisticated multi-layer urban canopy schemes. The implementation of the BEP urban
canopy scheme into METRAS provides a tool to address important research questions on the
effect of urban land use changes at the regional scale.
In order to investigate the problem of thermal modifications due to urbanisation it was also
necessary to select a study area to model. London was chosen for this study, since it is a major
world urban centre, which has grown considerably in time, and for which key environmental,
social and economic impacts associated with climate change have been identified (LCCP 2002).
There is very limited numerical modelling work on the London area and the possible effects of
the urban structure on climate.
This work is important because it explores whether the climate in the London region has been
influenced by the urban structure, as well as ascertaining which properties of the city which are
most important in terms of modifying climate. By running the model with different land use
5