The Climate System

Abstract

The Mediterranean region has a highly distinctive climate due to its position between 30 and 45°N to the west of the Euro-Asian landmass. With respect to the global atmospheric system, it lies between subtropical high pressure systems to the south, and westerly wind belts to the north. In winter, as these systems move equatorward, the Mediterranean basin lies under the influence of, and is exposed to, the westerly wind belt, and the weather is wet and mild. In the summer, as shown in Figure 3.1, the Mediterranean lies under subtropical high pressure systems, and conditions are hot and dry, with an absolute drought that may persist for more than two or three months in drier regions. Climates such as this are relatively rare, and the Mediterranean shares its winter wet/summer dry conditions with locations as distant as central Chile, the southern tip of Cape Province in South Africa, southwest Australia in the Southern Hemisphere, and central California in the Northern Hemisphere. All have in common their mid-latitude position, between subtropical high pressure systems and westerly wind belts. They all lie on the westerly side of continents so that, in winter, when the westerly wind belts dominate over their locations, they are exposed to rain-bearing winds. In the Köppen classification (Köppen 1936), these climates are known as Mediterranean (Type Cs, which is subdivided in turn into maritime Csb and continental Csa). The influence of the Mediterranean Sea means that the Mediterranean-type climate of the region extends much further into the continental landmass than elsewhere, and is not restricted to a narrow ocean-facing strip. Nevertheless, within the Mediterranean region climate is modified by position and topographic influences can be important. The proximity of the western Mediterranean to the Atlantic Ocean gives its climate a maritime flavour, with higher rainfall and milder temperatures throughout the year. The eastern Mediterranean lies closer to the truly continental influences of central Europe and Asia. Its climate is drier, and temperatures are hotter in summer and colder in winter than in the west. Annual rainfall is typically around 750 mm in Rome, but only around 400 mm in Athens.

Speleothem evidence for late Holocene climate variability and floods in Southern Greece

“…During NCPI(−) circulation tends to be stronger from the southwest favoring higher temperatures and wetter conditions (Kutiel and Benaroch, 2002;. Another important control on winter temperature variability is the Mediterranean Oscillation (MO), calculated from the differences in pressure between e.g., Cairo and Algiers (Feidas et al, 2004;Harding et al, 2009). During positive MO a southward flow of cool air over Greece can be facilitated in connection to enhanced frequency and persistence of low pressures over the central Mediterranean (Feidas et al, 2004).…”

Vegetation, fire, climate and human disturbance history in the southwestern Mediterranean area during the late Holocene

“…The summer is dry and hot, with the winter being humid and mild. More specifically, the climate of this region is strongly influenced by factors that control the North Atlantic Oscillation (NAO; Harding et al, 2009). Other important processes controlling climate in this area are the seasonal expansion northward of the Hadley Cell circulation (Roberts et al, 2011) due to heating of the North African landscape and the indirect effects of the African and Asian monsoons as expressed in regions to the south and southeast (Lionello et al, 2006).…”

A chronology of alluvial fan response to Late Quaternary sea level and climate change, Crete

“…The Mediterranean basin lies at the climatic boundary between arid North Africa and temperate mid-latitude Europe (Harding et al, 2009;Tzedakis, 2009;Rohling et al, 2015) and is, consequently, highly sensitive to environmental change. This sensitivity is well-expressed in the palaeo-record (Allen et al, 1999;Moreno et al, 2004).…”