Urban impacts on climate - The Global Climate System: Patterns, Processes, and Teleconnections - page 215

Table 7.1 Flowchart showing the range of spatial scales in an urban
environment that contribute to urban climate. Each unit interacts to contribute
to a range of processes that create alterations to urban climate, some of which
are listed in the right-hand column (based on Arnfield 2003 )

Urban unit (smallest to
largest size)

Interacting processes (occur between
each unit level)

Roof and walls
# Shortwave solar energy interception

Buildings, paved areas, green
space

Longwave radiation release
Artificial heat release

# Increased urban temperatures

Urban canyons Increased roughness

# Reduced wind speed

City blocks Altered wind direction

# Urban circulation development

Neighborhoods Convective cloud enhancement

# Increased downwind precipitation

Land use zones Excess water runoff

# Reduced evaporation/transpiration

Urban area

major source of anthropogenic greenhouse gas emissions, and create or con-
tribute to aerosol plumes that can transport many thousands of kilometers down
wind (Oke 1997 ). Critical, however, to urban impacts on climate is the impor-
tance of urban unit scale and spatial variability (see Table 7.1 ).

7.2 Highlights in the history of urban climate research
Research and analysis of cities and their impacts on the atmosphere are not new
(see www.urbanclimate.net for a useful historical bibliography). Air quality,
rather than climate itself, was defined as a problem first. John Evelyn in 1661, in
his pamphlet Fumifigum, describes the sulfur and smoke from the city of
London. He identified air pollution as a major health problem, a fact not formally
recognized by the medical profession until 300 years later! The first known
urban climate study was published in 1833 by Luke Howard, an alchemist who
also provided the first description of cloud types. Using methodologies and
equipment the quality of which would not be acceptable today, Howard estab-
lished differences in climate between London and the surrounding countryside.
In 1925, the first circulation pattern associated with an urban center was identi-
fied in Munich.