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of such model output with urban-based observations show this approach to be
too simplistic and many of the features of urban climate are not captured.
Increasingly, more complex models are being developed, which incorporate
the morphology and complexity of surface materials in urban environments
and their results are showing significant promise. For example, the Town
Energy Balance (TEB) model of Masson ( 2000 ) treats the surface as an urban
canyon without orientation. With such models, incorporated into a meso-
scale model it is possible to have areas with different height to width
characteristics across a city. It is possible to begin to incorporate the spatial
variability of urban morphology within and between cities. At smaller scales,
three-dimensional dispersion models now take into account the flow pro-
cesses with the RSL (Figure 7.4 ), and three-dimensional energy balance
models capture the variability of sky view factor within urban canyons.
With more powerful computers, models at all scales will capture more
completely the fundamental exchange processes generating urban climates
with greater spatial resolution, accounting more fully for the geometry and
diversity of construction materials of cities, providing better simulations of
urban climates as a result.
7.3.6 Concluding comments
In many instances urban climate effects are similar to, and maybe even
greater than, those changes predicted from global climate models (GCM).
However, there is no one urban effect; cities are diverse as are their settings.
Great care must be taken in observing urban climates, with particular atten-
tion to the scale of interest and the scale of the observations, and in general-
izing results to other locations. Greater insight into urban climates is being
gained by studies that measure and model the fundamental surface-
atmosphere exchanges of energy, matter, and momentum in these settings.
Given that cities worldwide are reaching an unprecedented size, in terms of
their number, area, and population, the magnitude and extent of urban effects
are increasing, with profound implications for energy consumption and
human health and well-being. Most growth in urban populations, approxi-
mately 90%, is occurring in countries of the developing world, where growth
rates, notably in Africa and Asia, are approximately 4% per year. In Europe
and North America, the issues associated with urbanization are different. On
these continents, the greatest urban growth took place a century ago; by 1995
more than 70% of the population was living in urban areas (World Resources
1996 ) (this proportion exceeds 90% in certain countries, for example,
Australia). Much of the population shift now underway involves movement
away from concentrated urban areas to extensive, sprawling metropolitan
regions, or to small- and intermediate-size cities. This is especially manifest
 
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