Environmental Engineering Reference
In-Depth Information
•
And, in terms of observational studies, are we measuring the correct variables at
the appropriate spatial and temporal scales to evaluate models?
Here we outline a methodology to undertake a comprehensive and controlled
evaluation of a range of urban surface energy balance schemes using a staged
methodology and carefully released evaluation data. The overall aim of the project is
to gain insight into the strengths and weaknesses of different classes of urban mod-
els, with particular focus on the level of complexity (physical understanding, data
requirements, spatial detail and temporal resolution) relevant for different applica-
tions. The purpose of this initial paper is two-fold: first, to describe the character-
istics of the urban models to be compared; and second, to outline the methodology
to be used in the overall study. Structured model evaluations such as this have
inherent value in identifying deficiencies in a community's modelling capabilities
(see for example, the outcomes of PILPS, Henderson-Sellers et al., 1993) and in
supporting the design of field experiments to collect key data for model runs and
evaluations.
11.2 Urban Surface Energy Balance Models
A wide range of approaches have been adopted to represent the surface energy
balance in urban areas. Here we present a broad list of urban surface energy
balance models (Table 11.1) for which each is given a code or acronym used
hereafter to describe it. Where multiple versions of the models exist, they are
differentiated.
11.2.1 Model Outputs
To be included in this comparison, a model must be able to predict the surface
energy balance fluxes representative of the local (or neighbourhood) scale. Many
of the models are also capable of calculating additional terms, typically air and sur-
face temperatures and wind speed, and providing more detailed flux information, for
example by facet, and these are recorded in Table 11.2. Notable differences between
models relate to whether the canyon is assumed to have an orientation and thus, sun-
lit or shaded walls at appropriate times of the day (e.g. CLMU, CAT, SUNBEEM),
or if the model is without orientation so that only one 'wall' is resolved and con-
sidered representative of the integrated urban domain (e.g. TEB). In the latter case,
there are three distinct built facets: wall, roof, and road. Obviously, the issue of sun-
lit or shaded facets also relates to roads (the floor of the canyon). The most detailed
models can calculate the spatial variability along facets (e.g. TUF3D). As an aside, it
should be noted that there are other models (e.g. CFD models) that simulate within-
canyon variations in more detail, although such micro-scale variations are not the
focus of this work.
Search WWH ::
Custom Search