eTheses Repository - University of Birmingham

appropriate value for these parameters to use in future work on the city of London is not
easy, and there is little available literature to assist in the choice.
Potential temperature [K]
Figure 4.16: Potential temperature (K) along the line y=0, z=10 m, as computed by the three
simulations with the internal temperatures behind urban walls and roofs (‘twini’ and ‘trini’) both set to
293 K (black line), 295 K (green) and 297 K (yellow) at 04:00 for the second day of simulation.
4.3.3 Sensitivity to the surface albedo
The sensitivity of the model to the albedo values of the urban surfaces was investigated.
The albedo of a surface is defined as its hemispherically and wavelength integrated
reflectivity (Taha 1997).
The difference in albedo between rural and urban surfaces is one of the factors which can
affect the surface energy balance in urban areas. The albedo for the urban area is typically
lower than that of the rural surroundings, and therefore less radiation is reflected back from
the urban area, which can lead to a higher heat content, thus contributing to the UHI
phenomenon (Oke 1987; Taha 1997; Atkinson 2003). A decrease in the UHI intensity is
111