noticeably in opposition to episodes of heavy precipitation which showed change
patterns. This general temporal tendency contained discernible regular time cycles
between wetter and drier periods.
In the western Mediterranean and the Balkans, the available recorded data shows
major moist cycles during the periods of 1900–1920, 1930–1956, and 1968–1980
with interim dry periods (Maheras 1987; Maheras and Kolyva-Machera 1990).
The forecasts from 22 models for Southern Europe and the Mediterranean
region, for the period 2050–2100, point to a significant decrease in rainfall, ranging
from 30 to 50%, while for countries of Northern Europe the previsions are opposite
for a rise between 30 and 50% (scenario A1B, from the AR4 Report). For most of
the Iberian Peninsula, there is a trend toward more rainy days excepting southeast
Spain where the reverse is expected with high rainfall amounts.
In all this context, the established consensus from climate projections is for
decreased precipitations from 4 to 27% in Southern Europe and Mediterranean
regions, whereas in Northern Europe it will increase between 0 and 16%. An
increase in drought periods associated with land degradation, along with a high
number of days with temperatures higher than 30 °C, is also expected (Giannakopoulos et al. 2005).
If the numerical models are broadly correct about precipitation changes in
response to increases in greenhouse gases, the droughts over the western
Mediterranean Basin could be symptomatic of growing human influence on
regional climate. Wetter conditions in the east might reflect the stronger influence of
aerosols in this area (Karas 2006). Giannakopoulos et al. (2009) cite Portugal as the
Mediterranean-influenced country where the modeling results of precipitation
profiles, under different emission scenarios, differ greatly, mainly due to intra- and
inter-annual rainfall variability. Apart from this source of variability, the remaining
differences in precipitation profiles are not statistically significant.
The characterization trends of precipitation in the Mediterranean Basin, should
consider the complexity of physical processes underlying precipitation. The use of
high-resolution updated models at smaller scales should be considered to take into
account the specificities of the Mediterranean Sea with uneven and rugged coastlines and smaller seas. Hence, the regional trends in the Mediterranean Basin
typically distort the scale of changes in precipitation at the local level. For example,
in much of North-Western Africa, Spain, Italy, and Greece for the period 1975–
1994, average precipitation was lower by 17% than during the preceding 20 years.
This contrasts with the conditions elsewhere in northern Africa and the eastern
basin, where average rainfall was higher over the same period (Karas 2006).
In any case, a long-term model for the Mediterranean region suggests that from
2050 onwards, precipitation will decrease markedly as the relative influence of
greenhouse gases grows (Karas 2006). However, some models are found to
underestimate year-to-year variability, with problems in reproducing the observed
trends when Spain and Greece are compared. This means that different underlying
physical processes are at stake, and further investigation on downscaled processes is
required.
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8 Fundamentals of Global Carbon Budgets and Climate Change
patterns. This general temporal tendency contained discernible regular time cycles
between wetter and drier periods.
In the western Mediterranean and the Balkans, the available recorded data shows
major moist cycles during the periods of 1900–1920, 1930–1956, and 1968–1980
with interim dry periods (Maheras 1987; Maheras and Kolyva-Machera 1990).
The forecasts from 22 models for Southern Europe and the Mediterranean
region, for the period 2050–2100, point to a significant decrease in rainfall, ranging
from 30 to 50%, while for countries of Northern Europe the previsions are opposite
for a rise between 30 and 50% (scenario A1B, from the AR4 Report). For most of
the Iberian Peninsula, there is a trend toward more rainy days excepting southeast
Spain where the reverse is expected with high rainfall amounts.
In all this context, the established consensus from climate projections is for
decreased precipitations from 4 to 27% in Southern Europe and Mediterranean
regions, whereas in Northern Europe it will increase between 0 and 16%. An
increase in drought periods associated with land degradation, along with a high
number of days with temperatures higher than 30 °C, is also expected (Giannakopoulos et al. 2005).
If the numerical models are broadly correct about precipitation changes in
response to increases in greenhouse gases, the droughts over the western
Mediterranean Basin could be symptomatic of growing human influence on
regional climate. Wetter conditions in the east might reflect the stronger influence of
aerosols in this area (Karas 2006). Giannakopoulos et al. (2009) cite Portugal as the
Mediterranean-influenced country where the modeling results of precipitation
profiles, under different emission scenarios, differ greatly, mainly due to intra- and
inter-annual rainfall variability. Apart from this source of variability, the remaining
differences in precipitation profiles are not statistically significant.
The characterization trends of precipitation in the Mediterranean Basin, should
consider the complexity of physical processes underlying precipitation. The use of
high-resolution updated models at smaller scales should be considered to take into
account the specificities of the Mediterranean Sea with uneven and rugged coastlines and smaller seas. Hence, the regional trends in the Mediterranean Basin
typically distort the scale of changes in precipitation at the local level. For example,
in much of North-Western Africa, Spain, Italy, and Greece for the period 1975–
1994, average precipitation was lower by 17% than during the preceding 20 years.
This contrasts with the conditions elsewhere in northern Africa and the eastern
basin, where average rainfall was higher over the same period (Karas 2006).
In any case, a long-term model for the Mediterranean region suggests that from
2050 onwards, precipitation will decrease markedly as the relative influence of
greenhouse gases grows (Karas 2006). However, some models are found to
underestimate year-to-year variability, with problems in reproducing the observed
trends when Spain and Greece are compared. This means that different underlying
physical processes are at stake, and further investigation on downscaled processes is
required.
296
8 Fundamentals of Global Carbon Budgets and Climate Change