Trends of the daily maximum temperatures in relation with the climatic change and the urbanization in the Athens basin

It is well known that the studies that associate the climatic changes with the greenhouse
effect, as a sequence of uninterruptedly ongoing figures in the concentration mainly of carbon
dioxide, have been focused on the trends of the mean temperature. On the other hand the
variability and the trends of the extreme temperature values have not been considered
sufficiently. We notice that the variability of the maximum and minimum temperature values
and generally of the extreme weather has direct economic and societal implications.
The interest in this paper is focused on the study of the trends of the daily and the monthly
maximum temperature during the warm months July and August for the time period from 1955
to 2000 in the wide Athens area and specifically measurements of the Nea Philadelphia and
Helliniko meteorological stations. Nea Philadelphia represents an immiscibly urban area
station, while Helliniko a coastal suburban area one. The specific sites were selected for the
comparative study of the temperature maximum trends in a time period which covers the
population growth in the area of Athens.
For the whole time period, the differences of the daily maximum temperature from the
corresponding 10-days period mean maximum temperatures per month were calculated for
each site. Then, the days with positive difference per month and per year as well as the
trends of the time-series for each station were recorded along with the statistical significance
of the regression slope’s value using the Student t-test distribution.
Furthermore, in order to identify the “warmest decade” in the time-series, a study of the daily
maximum temperature trend for the months July and August was performed for each decade
followed by a test for the statistical significance of the slope coefficient.
It is known that the presumable differences of the temperature time-series depend on the
influence of the urbanization, the modification of the natural suburban environment and / or on
the stations’ displacement. Based on these facts, we present more in this paper the
conclusions of a comparative study of the results regarding each station analytically as well
as the interpretation of the results concerning all the stations as an ensemble.