FIGURE 2
Projected climate in Illinois in
2030 and 2090 using Canadian
and Hadley model projections
(Adams and Gleick, 2000)
Limitations of this method arise when there are only short-
climate changes in other areas.  Paved surfaces and building
term records for a period of increased temperature.
materials absorb, rather than reflect, the sun’s heat, causing
Drought conditions and higher temperature periods rarely
the temperature in the city core to rise.  These core areas
last long enough to cause widespread changes in ground
are often one to 10 degrees Fahrenheit (.56 to 5.6 Celsius)
water levels and flow patterns.  When this occurs, historical
warmer than surrounding suburbs (Goddard Space Flight
analogues may be used in conjunction with physically
Center 2002).  The additional heat rises, causing changes in
based scenarios like General Circulation Models, to predict
air circulation and often forming rain clouds.  This phe-
climate changes.
nomenon has been documented in several large cities,
such as Atlanta, where rainstorms were often produced
Climate Transposition
downwind of the city.
Climate Transpositions or Spatial Analogues work on the
Although small in nature, urban heat islands can be used in
principal that one may be able to predict future climate
conjunction with other climate predicting methods to
scenarios by looking at a similar climate in a warmer region
estimate changes in the hydrologic cycle, such as the
nearby.  Ideally, analogous locations will have similar
amount and timing of precipitation.
topography, ecozones and land use however, this is rarely
the case.  For example, the climate of Toronto, Ontario has
In the past century there has been an increase in average
been predicted to resemble the climate of southern Ohio in
annual temperature of 0.6 degrees Celsius.  The 1990s
the future (Government of Canada and U.S. EPA, 1995).
were the warmest decade in the past 100 years, with seven
However, Toronto is under the direct influence of the Great
of the ten warmest years occurring within this decade.
Lakes, whereas southern Ohio experiences a lesser
However, the Great Lakes themselves have a significant
moderating effect, being farther away from the Great Lakes.
influence over the climate; the large bodies of water are
The effect of Lake Ontario on Toronto’s climate cannot be
able to moderate temperature and influence wind and
accurately estimated, unless General Circulation Models or
precipitation patterns on a regional scale.  For this reason,
Regional Climate Models also are used.
the impacts of rising concentrations of CO2 and other
greenhouse gases on the climate patterns of the Great
Predictions from the Hadley and Canadian models have
Lakes region are not so easily predicted.  Moreover, without
transposed the climate of Illinois, shown in Figure 2.  The
being able to predict changes to temperature and precipita-
Canadian model predicts a more continental climate, much
tion patterns, influences on ground water levels and
like the central U.S.  The Hadley model shows a contrasting
recharge are unknown.
prediction, with Illinois having a more maritime climate
similar to Massachusetts.  Despite the differences in spatial
transposition, it can be assumed that the climate of Illinois
4.3.5
The Effect on Ground Water
is going to get warmer, but we cannot tell if there will be
more or less summer precipitation.
Changes in temperature and precipitation resulting from
climate change and variability will cause an alteration to the
hydrologic cycle.  The proposed increases in temperature
4.3.4
Urban Heat Islands
will likely cause an increase in evaporation, decrease in
runoff, and reduction in stream flow, all leading to a
Changes in climate have been observed within cities due to
reduction in ground water recharge.  The frequency of
the Urban Heat Island Effect and may be used to predict
extreme weather events, such as thunderstorms, tornadoes
98