Geoscience Reference
In-Depth Information
Figure 2.15 shows the result obtained after modeling: temp_Aug = f(dist-town),
where August temperatures (temp_Aug) are estimated by analyzing the distance
to town, which can be represented by the following equation: temp_Aug = 203 +
(-0.014dist-town).
Figure 2.15 confirms what was expected: temperature is maximum (>20°C) in
areas that are recognized by CLC as being dense developed towns, and then
decreases the further towards the area's periphery where temperature reaches its
minimum value of <18°C. In other words, temperature is at its lowest in areas that
are furthest away from a town center or in areas that are located between two large
towns.
Nevertheless, there is one main problem with this map: the variable “distance to
town” is first considered as explanatory during the analysis phase. During the
modeling phase, however, this independent variable then becomes the cause of the
variations in temperature that exist. For example, from the map we find that there
are rather small urban areas such as Château-Thierry, which has an exacerbated
influence on its surrounding area as far as temperature is concerned.
The quadratic function equation changes this trend slightly; it reduces the
influence that a town center can have on temperature. The more we expect large
cities to have their own distinct heat islands, the more surprising it would be for
small villages to have the same influence on temperature. The validity of the
relationship that exists between these two variables needs to be confirmed to be used
as a reliable model.
In order to make this point more understandable we have reproduced correlation
calculations for only a select number of the largest cities in France.
Figure 2.16.
Temperature variation for February and August in the Paris region. Variation
temperature is calculated in relation to the variable “distance from the town center”
Paris, for example, is made up of 122.5 km
2
dense buildings (which is
represented by CLC code 1). The polygon's barycenter is located near the “Ile de la
Cité”, which is at the heart of Paris. Fifty-six climatological stations within a
distance of 50 km from the barycenter were chosen for the study. The correlation
between the temperature average for February and August (the dependent
variables), and the distance of the stations to the center of Paris (the independent
