The Mediterranean climate can be defined as a transition zone between temperate and dry tropical climates.
In summer, areas with Mediterranean climates show hot dry conditions like those that prevail in the neighboring subtropical deserts.
The Mediterranean climate is relatively recent, having appeared for the first time in the Pleistocene.
The duration of the hot dry period is of great importance in determining the nature of the landscape within the Mediterranean biome, as it is the most important environmental factor.
The Mediterranean climate includes a range of transitions, from those of wet climates to those found in the boundaries with desert climates: thus it extends from subhumid to semi-arid.
Many classifications have been proposed for Mediterranean subclimates, based on the use of different criteria for combining rainfall and temperature data to determine the dry period.
Classifications based on these values suggest the following subclimates: arid Mediterranean (20 < Q [less than or equal to] 30, precipitation 12-20 in/yr or 300-500 mm/yr), semi-arid Mediterranean (30 < Q [less than or equal to] 50, precipitation 20-27 in/yr or 500-700 mm/yr), subhumid Mediterranean (50 < Q [less than or equal to] 90, precipitation 27-39 in/yr or 700-1,000 mm/yr), and humid Mediterranean (Q>90, precipitation >39 in/yr or 1000 mm/yr).
If we use the mean temperature of the coldest month, we can make the following division: a hot Mediterranean climate (m [less than or equal to] 45[degrees]F or 7[degrees]C), where there are no frosts; temperate Mediterranean (37[degrees]F or 3[degrees]C < m [less than or equal to] 45[degrees]F or 7[degrees]C), where there are occasional frosts; cool Mediterranean (32[degrees]F or 0[degrees]C [less than or equal to] m < 37[degrees]F or 3[degrees]C), where there are frequent frosts; and lastly cold Mediterranean (m < 32[degrees]F or 0[degrees]C), with long periods of freezing weather.
Minimum values are used to define subclimates because of the great importance of cold as a factor in the Mediterranean climate.
The third section, dealing with human beings in the Mediterraneans, consists of four chapters.
This volume would not have been possible without the invaluable advice of Francesco di Castri, one of the leading experts on the Mediterraneans of the world, and who has done much to further their understanding.
This presentation is not intended to be a summary of the text it introduces, so it would be inappropriate to explain the characteristics and the geographical distribution of the Mediterranean areas.