ancient cities

848 Urban Climate
Urban archaeology is practiced around the
world. Many of the world’s great cities sponsor
excavations, provide interpretations of them to
the public, and even open excavations to the public.
Well-known urban archaeological excavations
are currently under way in Saint Augustine,
Florida; Sacramento, California; Rome, Italy; and
Buenos Aires, Argentina.
Mark P. Leone, Matthew D. Cochran, and
Stephanie N. Duensing
Further Readings
Cantwell, Anne-Marie and Diana diZerega Wall. 2001.
Unearthing Gotham: The Archaeology of New York
City. New Haven, CT: Yale University Press.
Garrioch, David and Mark Peel. 2006. “Introduction:
The Social History of Urban Neighborhoods.” Journal
of Urban History 32(5):663–76.
Gillette, Howard, Jr. 1990. “Rethinking American Urban
History: New Directions for the Posturban Era.”
Social Science History 14(2):203–28.
Harvey, David. 1989. The Urban Experience. Baltimore:
Johns Hopkins University Press.
Mayne, Alan and Tim Murray, eds. 2001. The
Archaeology of Urban Landscapes: Explorations in
Slumland. Cambridge, UK: Cambridge University Press.
Mrozowski, Stephen A. 1987. “Exploring New England’s
Evolving Urban Landscape.” Pp. 1–10 in Living in
Cities: Current Research in Urban Archaeology, edited
by E. Staski. Special Publication of the Society for
Historical Archaeology.
Rothchild, Nan. 1990. New York City Neighborhoods:
The 18th Century. San Diego, CA: Academic Press.
Symonds, James. 2004. “Historical Archaeology and the
Recent Urban Past.” International Journal of Heritage
Studies 10(1):31–48.
Upton, Dell. 1992. “The City as Material Culture.”
Pp. 51–74 in The Art and Mystery of Historical
Archaeology, edited by A. Yentsch and M. Beaudry.
Boca Raton, FL: CRC Press.
Yamin, Rebecca. 2007. “Review Essay: The Tangible
Past: Historical Archaeology in Cities.” Journal of
Urban History 33:633–44.
Ur b a n cl i m a t e
Urban climates are climates modified by the presence
of urbanized areas. Urban climates include
modifications to all the main elements that comprise
our weather and climate: temperature, radiation,
wind flow, humidity, atmospheric composition,
clouds, and precipitation. These changes come
about because urbanization creates significant
modifications to the land surface and these modifications
affect how energy and mass are exchanged
between the surface and the atmosphere. Urban
climates now affect nearly half of the world’s
population. Most residents of developed nations
live in cities while less-developed nations have
experienced recent rapid rates of urbanization and
the emergence of megacities.
Urban climates represent an unintentional or
inadvertent change to climates. Urban climates are
superposed on both the background climate of a
location as well as any regional climate effects due
to the landscape such as a coastal or valley location
of a city. Modified urban climates influence
the energy and water use in cities, have health
implications for urban inhabitants, affect biological
activity, and modify the weather downwind of
cities. Whereas most impacts of urban climates are
confined largely to urban areas themselves, some
aspects of urban climate can affect the environment
downwind of cities, influencing the atmosphere
and climates on scales much larger than the
city itself, thus providing a link between global
environmental change and urbanization.
Scales of Urban Climates
Urban climates refer to climates over surfaces as
small as a few square meters (micro-scale variability
between, e.g., a front garden and a paved driveway),
up to several tens of kilometers that encompass
an entire metropolitan area. An important scale
distinction for urban climate is that of the urban
canopy layer and the urban boundary layer. The
urban canopy layer refers to the layer of air
extending from the surface up to approximately
the mean height of the canopy elements—the
buildings, trees, and other objects that make up the
surface of the city. The surface of the city has a
distinct three-dimensional form to it, which plays
an important role in determining the nature of
urban climates. The urban boundary layer lies
above the urban canopy layer and extends upward
in the atmosphere to where the influence of the
surface is no longer felt on a daily basis. This