Analysis of Mediterranean Climate Data: Measured and Modelled
129
with the individual SLP time series.
11. For the pressure observations which make up the MPI, it is only in summer that
the sign of the correlation between the SAls and the SLP observations is always
opposed, with Gibraltar having a negative correlation and Lod Airport a positive
sign. In this season, and for all four SAl regions, the correlation with the MPI
is always higher than it is with the individual SLP time series.
iii. In winter, spring and autumn, there is a negative relationship between all the
SAls and the pressure at both Lod Airport and Gibraltar. The only exception is
for the western Mediterranean in spring. The highest correlations are with
Gibraltar, with the exception of the eastern Mediterranean.
We conclude from this analysis that the MPI is only a true oscillation, having a
real relationship with rainfall amounts over the Mediterranean region, in the
summer months.
Finally, we correlated the NAO and the MPI values to establish whether the MPI
is an independent entity from the NAO. The results for the four seasons are as
follows:
Winter
Spring
Summer
Autumn
0.72
0.37
-0.13
0.30
The correlation in winter is significant at the 99% level, and the spring and
autumn results are significant at the 95% level. This result suggests that in summer
(but only in this season) the MPI is a phenomenon truly independent of the NAO.
4 Understanding What May Happen in Future
Information is available from a whole range of climate models, both coarseresolution General Circulation Models and, increasingly, finer-resolution Regional
Climate Models. As an example for the Mediterranean, Table 3 shows the predicted
composite changes, based on four recent climate model simulations. Between both
decades the greatest change in temperature occurs in summer and the smallest
change is in spring. For precipitation, the greatest change occurs in spring and the
smallest in winter. In the latter season, between 2030-1990 there is a decrease and
between 2090-1990 there is an increase.
5 Understanding the Relationship Between Present and
Future Climates
It is important to understand the relationships between present-day observational
data and the future as predicted by climate models. This allows us to address such
129
with the individual SLP time series.
11. For the pressure observations which make up the MPI, it is only in summer that
the sign of the correlation between the SAls and the SLP observations is always
opposed, with Gibraltar having a negative correlation and Lod Airport a positive
sign. In this season, and for all four SAl regions, the correlation with the MPI
is always higher than it is with the individual SLP time series.
iii. In winter, spring and autumn, there is a negative relationship between all the
SAls and the pressure at both Lod Airport and Gibraltar. The only exception is
for the western Mediterranean in spring. The highest correlations are with
Gibraltar, with the exception of the eastern Mediterranean.
We conclude from this analysis that the MPI is only a true oscillation, having a
real relationship with rainfall amounts over the Mediterranean region, in the
summer months.
Finally, we correlated the NAO and the MPI values to establish whether the MPI
is an independent entity from the NAO. The results for the four seasons are as
follows:
Winter
Spring
Summer
Autumn
0.72
0.37
-0.13
0.30
The correlation in winter is significant at the 99% level, and the spring and
autumn results are significant at the 95% level. This result suggests that in summer
(but only in this season) the MPI is a phenomenon truly independent of the NAO.
4 Understanding What May Happen in Future
Information is available from a whole range of climate models, both coarseresolution General Circulation Models and, increasingly, finer-resolution Regional
Climate Models. As an example for the Mediterranean, Table 3 shows the predicted
composite changes, based on four recent climate model simulations. Between both
decades the greatest change in temperature occurs in summer and the smallest
change is in spring. For precipitation, the greatest change occurs in spring and the
smallest in winter. In the latter season, between 2030-1990 there is a decrease and
between 2090-1990 there is an increase.
5 Understanding the Relationship Between Present and
Future Climates
It is important to understand the relationships between present-day observational
data and the future as predicted by climate models. This allows us to address such