eTheses Repository - University of Birmingham

More recent efforts to parameterise urban effects on the thermodynamic and momentum fields
are reviewed in Craig et al. (2002), Masson (2006) and Martilli (2007). The nature of the
parameterisation used should depend on the aim of the simulation and the CPU power available.
Recent efforts have focused on the dynamic or the thermodynamic properties of the urban
surface (Masson 2006). The dynamics of the urban surface can be parameterised by a change in
roughness length based on the characteristics of the urban area (e.g. Bottema 1997), or by
introducing a drag term (e.g. Uno et al. 1989; Brown 2000; Ca et al. 2002; Martilli et al. 2002;
Dupont et al. 2004) to the momentum and turbulent kinetic energy (TKE) equations in order to
represent the drag induced by the presence of buildings (this approach is derived from that used
for vegetation canopies).
The thermodynamic effects of the surface can be parameterised by modifying the urban surface
energy balance in a number of ways, aimed at either finding a relationship between heat storage
and net radiation, or solving the physics of the problem (Martilli 2007). A simple approach is
based on the semi-empirical objective hysteresis model (OHM), an empirical formulation for
heat storage, of Grimmond et al. (1991) together with the LUMPS scheme (Grimmond et al.
2002) to estimate the turbulent fluxes. However this approach is limited by the availability of
field data. Another simple approach to represent one of the urban effects consists in incorporating
an anthropogenic heat term (Fan et al. 2005), although the success of this will also be dependent
on the availability of extensive data on energy consumption and traffic. More sophisticated
physical approaches consist in parameterising the shadowing and trapping of radiation in the
canyon (Masson 2000) as well as the advanced SM2-U approach of Dupont et al. (2004) which
uses a modified soil module which computes the heat fluxes and surface temperatures following
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