As the global climate changes, the frequency of extreme events in the
Mediterranean region will change both in relation to the average climate as to
climate flutuations. Warmer conditions over the Mediterranean region should lead
as to an increase of extremely high temperatures as to a decrease in extremely
low-temperature events. An increase in drought periods is related to the previously
mentioned high frequency of days during which the temperature exceeds 30 °C
(Giannakopoulos et al. 2005). In areas experiencing a general decrease in precipitation, droughts are likely to become more frequent.
Heatwaves, droughts, or floods are also likely to be more frequent and violent.
This tendency for the higher occurrence of extreme events has been noted since the
mid of the twentieth century, with decreases in global frequency of cold days and
nights and increases of warm days and nights (Hartmann et al. 2013). Likewise,
heatwave frequency has increased in large parts of Europe, Asia, and Australia
during this period. In the same way, it is likely that from about 1950 onwards, the
number of heavy precipitation events over land has increased in more regions than
it has decreased (AR5, Report).
Similarly, in areas experiencing a general decrease in precipitation, droughts are
likely to become more frequent, as the probability of dry days and the length of dry
spells increases. The converse is true for areas where precipitation increases. Precipitation events changed abruptly in 1996, with drying areas suddenly experiencing extreme wet conditions and vice versa (WMO 1997). It was also reported
that the probability of a dry spell lasting more than 30 days in summer in Southern
Europe would increase with the doubling of atmospheric carbon dioxide concentration, by a factor between two- and fivefold (Kattemberg et al. 1996). Extreme
precipitation events over most of the mid-latitude land masses and over wet tropical
regions will likely become also more intense and more frequent.
Alpert et al. (2002) identified a paradoxical increase in Mediterranean extreme
daily rainfall, in the period 1951–1995, despite a decrease in the total precipitation.
This so-called paradox reflects a presumable scenario of the existence of a substantial change in the rainfall distribution over the Mediterranean area wherein the
“increase of variance of the rainfall distribution overcomes the reduction of the
mean.”
The same author proposed 6 rainfall daily categories as powers of 2, from
(A) light: 0–4 mm/day; (B) light–moderate: 4–16 mm/day; (C1) moderate–heavy:
16–32 mm/day; (C2) heavy–torrential: 32–64 mm/day; (D1) 64–128 mm/day; and
(D2) Torrential: ! 128 mm/day up. This enables the evaluation of several rainfall
categories relative to rainfall totals and how these rainfall classes vary with time. An
alternative non-discrete approach would be the use of gamma distribution and the
analysis of changes in the shape and scale parameters (e.g., Groisman et al. 1999).
The rainfall trends were analyzed in 265 Mediterranean stations distributed across
the following countries: Spain (182 stations), Italy (42 stations), Cyprus (3), and
Israel (38). It was found that, for example, in Spain, the torrential category contribution toward the total annual rainfall increased significantly over the 45-year
period. On the other hand, the classes C1 and C2, contributing to about half of the
total rainfall, decreased significantly, dropping from about 49% in the early 1950s
298
8 Fundamentals of Global Carbon Budgets and Climate Change
Mediterranean region will change both in relation to the average climate as to
climate flutuations. Warmer conditions over the Mediterranean region should lead
as to an increase of extremely high temperatures as to a decrease in extremely
low-temperature events. An increase in drought periods is related to the previously
mentioned high frequency of days during which the temperature exceeds 30 °C
(Giannakopoulos et al. 2005). In areas experiencing a general decrease in precipitation, droughts are likely to become more frequent.
Heatwaves, droughts, or floods are also likely to be more frequent and violent.
This tendency for the higher occurrence of extreme events has been noted since the
mid of the twentieth century, with decreases in global frequency of cold days and
nights and increases of warm days and nights (Hartmann et al. 2013). Likewise,
heatwave frequency has increased in large parts of Europe, Asia, and Australia
during this period. In the same way, it is likely that from about 1950 onwards, the
number of heavy precipitation events over land has increased in more regions than
it has decreased (AR5, Report).
Similarly, in areas experiencing a general decrease in precipitation, droughts are
likely to become more frequent, as the probability of dry days and the length of dry
spells increases. The converse is true for areas where precipitation increases. Precipitation events changed abruptly in 1996, with drying areas suddenly experiencing extreme wet conditions and vice versa (WMO 1997). It was also reported
that the probability of a dry spell lasting more than 30 days in summer in Southern
Europe would increase with the doubling of atmospheric carbon dioxide concentration, by a factor between two- and fivefold (Kattemberg et al. 1996). Extreme
precipitation events over most of the mid-latitude land masses and over wet tropical
regions will likely become also more intense and more frequent.
Alpert et al. (2002) identified a paradoxical increase in Mediterranean extreme
daily rainfall, in the period 1951–1995, despite a decrease in the total precipitation.
This so-called paradox reflects a presumable scenario of the existence of a substantial change in the rainfall distribution over the Mediterranean area wherein the
“increase of variance of the rainfall distribution overcomes the reduction of the
mean.”
The same author proposed 6 rainfall daily categories as powers of 2, from
(A) light: 0–4 mm/day; (B) light–moderate: 4–16 mm/day; (C1) moderate–heavy:
16–32 mm/day; (C2) heavy–torrential: 32–64 mm/day; (D1) 64–128 mm/day; and
(D2) Torrential: ! 128 mm/day up. This enables the evaluation of several rainfall
categories relative to rainfall totals and how these rainfall classes vary with time. An
alternative non-discrete approach would be the use of gamma distribution and the
analysis of changes in the shape and scale parameters (e.g., Groisman et al. 1999).
The rainfall trends were analyzed in 265 Mediterranean stations distributed across
the following countries: Spain (182 stations), Italy (42 stations), Cyprus (3), and
Israel (38). It was found that, for example, in Spain, the torrential category contribution toward the total annual rainfall increased significantly over the 45-year
period. On the other hand, the classes C1 and C2, contributing to about half of the
total rainfall, decreased significantly, dropping from about 49% in the early 1950s
298
8 Fundamentals of Global Carbon Budgets and Climate Change