Geoscience Reference
In-Depth Information
Table 7.5 General summary of the impacts of cities on the local and
regional climate, based on Arnfield ( 2003 ) and the discussion in this chapter
Air urban heat island strength
Reduced by increasing wind speed
Reduced by increasing cloud cover
Greatest during anticyclonic conditions
Best developed in summer
Greatest at night
Increases with increasing urban population, size, building density
UHI does not always exist
UCI can occur during the day and in parks
Rates of heating and cooling in the city are generally lower than the
countryside
Cumulative impacts of urban canyons are important
UHI enhances convection and cloud formation
Urban effects on other parameters
Wind speed is reduced through friction and turbulence
Light winds may be increased though canyon channeling
Coriolis force is reduced, causing changes in wind direction
Urban canyons change the wind direction through channeling
Urban canyon vortices are important to energy exchanges and
cross-canyon flow
Sensible heat and storage heat dominate the energy balance in canyons
Evaporation is minimal, runoff is maximized on urban surfaces
Actual humidity is lower, especially in afternoon/evening
Added particulate matter enhances cloud formation
Extra convection and turbulence enhance downwind precipitation
STADTKLIMA, a German-based urban climate website, provides a very
useful bibliography on urban climate, www.urbanclimate.net.
UNEP, United Nations Environment Programme, summarizes the state of
the world's cities and provides web links to urban projects, www.unep.org/
themes/urban.
7.12 References
Arnfield, A., 2000. Micro- and mesoclimatology. Progress in Physical Geography, 24, 261-271.
2003. Two decades of urban climate research: a review of turbulence exchanges of energy
and water and the urban heat island. International Journal of Climatology, 23, 1-16.
Arnfield, A. and Mills, G., 1994a. An analysis of circulation characteristics and energy budget
of a dry, asymmetric, east-west urban canyon: I. Circulation characteristics. International
Journal of Climatology, 14, 119-134.
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