FUMAPEX Experience of Model Urbanisation - Meteorological and Air Quality Models for Urban Areas - page 63

3. ECN module: Based on the detailed urban area soil and sublayer SM2-U model
(Dupont and Mestayer, 2004; Dupont et al., 2004). First it was first tested with
the large eddy simulation SUBMESO research model and then considered for
incorporation into the DMI-HIRLAM NWP model.
4. Combined module: This includes all non-overlapping mechanisms from the
SM2-U and BEP models. It was used in MM5 (Dupont et al., 2004) and applied
to Paris by CORIA.

8.3 Results and Recommendations

8.3.1 Experience of Model Urbanisation

The range of improvement made by the FUMAPEX participants is summarized in
Table 8.1. Many of the parameterisations were evaluated using data sets collected as
part of the BUBBLE and ESCOMPTE projects. Implementation of the urban mod-
ules significantly improved the forecasted meteorological fields for urban areas. The
first module, the cheapest way to “urbanise”, can be easily implemented into oper-
ational NWP models as well as into Regional Climate Models. The second mod-
ule, although more expensive ( 5-10% computational time increase), provides the

possibility to consider the energy budget fluxes inside the urban canopy. However,
this approach is sensitive to the vertical resolution of NWP models and is not very
effective if the first model level is greater than 30 m. Therefore, an increase in the
vertical resolution of current NWP models is required. The third module is con-
siderably more expensive computationally than the first two. It provides the pos-
sibility to accurately study the urban soil and canopy energy exchange including
the water budget. Consequently, the second and third modules are recommended
for use in advanced urban-scale NWP and meso-meteorological research models.
This will be demonstrated for NWP models in a forthcoming paper. The third mod-
ule may be very useful for implementation into research submeso-scale or micro-
meteorological models (e.g., SUBMESO) for large eddy simulation or assessment
(non-prognostic) studies. The first and second modules can be also used as urban
interfaces or post-processors of NWP data for UAQ models.
Simulation results with these urban modules show that the radiation budget does
not differ significantly for urban compared to rural surfaces, as the increased loss of
a net longwave radiation is partly compensated by a gain in net shortwave radiation
due to a lower albedo. The turbulent fluxes of sensible and latent heat, as well as
their ratio, are variable and dependent in particular, on the amount of rainfall during
the preceding period. The storage heat flux is usually significantly higher in urban
areas compared to densely vegetated surfaces. This cannot be explained entirely by
a higher thermal inertia, as this quantity is only slightly higher for urban than rural
environments. Other factors of importance are the reduced moisture availability and
the extremely low roughness length for heat fluxes. The anthropogenic heat flux, a
typical urban energy flux, is absent in rural or natural areas.

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