Climate, Climate Variability and Impacts in the Mediterranean Area: An Overview
69
is even higher than for temperature. Sometimes such trends are deduced by linear
trend analysis extended over hundred and more years and the trend is mainly
determined by the higher precipitation in the early 20 th century while presently such
trends are not significant. Fig. 16 shows such an example taken from do 6 and Roxo
(2001). The red line shows the impressive trend if the whole period from 1931 -
1997 is taken into account. Considering the large interannual variability the trend
from 1952 - 1997 (green line) is very small and cannot be regarded as significant
and if the years 1931 - 1951 are looked at the trend is very large and positive.
Another example can be found in Lopez-Bermudez et al. (1999), where the 120
years negative rainfall trend of Murcia, Spain, is solely determined by high
precipitation around 1890, while, if started in 1910, the trend would have a positive
sign. These examples clearly indicate that linear regression is a dangerous tool to
identify climate change, it depends very much on the interval chosen. The data for
the last two years are not yet released for analysis and it is very likely that because
of the high precipitation rates at least in some areas the trend of the annual
precipitation of the last years may even be reversed. It needs an effort to merge these
data sets and evaluate them under a superordinate point of view and with
commensurable methods to obtain a consistent picture of climatological synergies
in the Mediterranean area.
Climate change may manifest itself more in an increase of the amplitude and
frequency of extreme events than in a smooth development of climate parameters.
Research must concentrate on the causes of these extreme events and their impact
on the annual totals. In this respect a distinction has to be made to what degree these
extreme events are determined by large scale respectively regional processes. The
flow of raw data to the analysts furthermore has to be accelerated to keep pace with
the development of the global greenhouse effect.
7.2 To What Degree Are the Processes Understood Which Drive
Climate Variability?
Through the atmosphere the Mediterranean basin is coupled to the North Atlantic
Ocean and its oscillations (NAO), the Indian monsoon, the Sahara, the Hadley
circulation and the polar front ofthe general circulation as schematically shown in
Fig. 17. Substantial progress has been achieved by regional investigations about
many details of the physical-biological system from groundwater respectively deep
sea to the free troposphere. SV AT models have been constructed which simulate
empirical results with great precision if initialized with correct data. Mesoscale
models are capable to describe quite well regional circulation systems of both the
atmosphere and the sea. The fact that notwithstanding these achievements present
days climate models are not capable to provide reliable answers for Mediterranean
regions is due to the lack of resolution and the accuracy of process descriptions in
these large scale models to account for the complex topography of the Mediterranean
basin, the internal variability of the Mediterranean Sea, the extraordinary manifold
ofland ecosystems, and the small scale processes like variability of the piezometric
69
is even higher than for temperature. Sometimes such trends are deduced by linear
trend analysis extended over hundred and more years and the trend is mainly
determined by the higher precipitation in the early 20 th century while presently such
trends are not significant. Fig. 16 shows such an example taken from do 6 and Roxo
(2001). The red line shows the impressive trend if the whole period from 1931 -
1997 is taken into account. Considering the large interannual variability the trend
from 1952 - 1997 (green line) is very small and cannot be regarded as significant
and if the years 1931 - 1951 are looked at the trend is very large and positive.
Another example can be found in Lopez-Bermudez et al. (1999), where the 120
years negative rainfall trend of Murcia, Spain, is solely determined by high
precipitation around 1890, while, if started in 1910, the trend would have a positive
sign. These examples clearly indicate that linear regression is a dangerous tool to
identify climate change, it depends very much on the interval chosen. The data for
the last two years are not yet released for analysis and it is very likely that because
of the high precipitation rates at least in some areas the trend of the annual
precipitation of the last years may even be reversed. It needs an effort to merge these
data sets and evaluate them under a superordinate point of view and with
commensurable methods to obtain a consistent picture of climatological synergies
in the Mediterranean area.
Climate change may manifest itself more in an increase of the amplitude and
frequency of extreme events than in a smooth development of climate parameters.
Research must concentrate on the causes of these extreme events and their impact
on the annual totals. In this respect a distinction has to be made to what degree these
extreme events are determined by large scale respectively regional processes. The
flow of raw data to the analysts furthermore has to be accelerated to keep pace with
the development of the global greenhouse effect.
7.2 To What Degree Are the Processes Understood Which Drive
Climate Variability?
Through the atmosphere the Mediterranean basin is coupled to the North Atlantic
Ocean and its oscillations (NAO), the Indian monsoon, the Sahara, the Hadley
circulation and the polar front ofthe general circulation as schematically shown in
Fig. 17. Substantial progress has been achieved by regional investigations about
many details of the physical-biological system from groundwater respectively deep
sea to the free troposphere. SV AT models have been constructed which simulate
empirical results with great precision if initialized with correct data. Mesoscale
models are capable to describe quite well regional circulation systems of both the
atmosphere and the sea. The fact that notwithstanding these achievements present
days climate models are not capable to provide reliable answers for Mediterranean
regions is due to the lack of resolution and the accuracy of process descriptions in
these large scale models to account for the complex topography of the Mediterranean
basin, the internal variability of the Mediterranean Sea, the extraordinary manifold
ofland ecosystems, and the small scale processes like variability of the piezometric