ancient cities

Urban Climate
Figure 1 Scales of Urban Climate Showing the Urban Boundary Layer and Urban Canopy Layer and Some of the
Processes and Effects of Urban Climate
Source: Adapted from Oke, T. R. 1997. “Urban Environments.” Pp. 303–27 in Surface Climates of Canada, edited by W. G.
Bailey, T. R. Oke, and W. R. Rouse. Montreal, QC, Canada: Queen’s University Press.
height shows significant variability between day
and night and under different weather conditions.
Under daytime, fair weather conditions it may be
1 to 2 kilometers above the city; at night it may be
a few hundred meters. (See Figure 1.)
Physical Basis for Urban Climates
Urbanization significantly changes the characteristics
of the land surface and the atmosphere. These
changes affect how energy and mass are exchanged
between the surface and the atmosphere and lead
to the creation of urban climates.
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Urban Surface. The urban surface characteristics,
including its geometric configuration; how well it
absorbs sunlight, emits radiative energy, and stores
heat; and the presence and amount of moisture are
important determinants of urban climates and help
explain how urban climates differ from the climates
of other natural systems.
Surface Geometry. Urban surfaces have complex
three-dimensional configurations and are said to
be “rough.” Rough urban surfaces exert more drag
on winds, resulting in a slowing of air flow over
urban areas and increased amounts of turbulence