Some define the mediterranean climate as where olive trees (Olea europaea) can successfully be grown and harvested — an ancient specimen at Le Pont du Gard in the south of France. Photo by Seán O'Hara

Characteristics of mediterranean climates

The world's five mediterranean-climate regions are bonded by the following set of characteristics1 that give them special distinction among the world's landscapes.

All regions are located between 32° and 41° north or south of the equator.

All regions are situated along the coast of oceans or the Mediterranean Sea; all, except large portions of the Mediterranean Basin, are on west coasts; strong, cold up-welling currents bathe the coastal regions with cool marine air and moderate winter temperatures, except for the Mediterranean Basin and South and Western Australia.

Annual rainfall is relatively low, with at least 65% falling in the winter half of the year.

Precipitation is primarily from rainfall, averaging 10.8in to 35.4in (.275m to .9m) yearly; though in some areas coastal fog and rare light snowfall contribute to the precipitation totals.

Sun intensity is high, especially in inland areas, due to clear, cloudless skies and low humidity; evapotranspiration rates can be twice as high inland, compared to those on the coast.

Summers are warm to hot, and winters are cool but mild, with one month averaging below 59° F (15° C); sub-freezing temperatures do not occur more than 3% of the total time.

Rugged mountains, frequently parallel to the coastline (except in Australia), influence and modify climatic patterns, forming distinct rain shadows and microclimates.

Native vegetation is dominated by arboreal and shrubby evergreen sclerophyllous plants adapted to climatic stresses of heat and aridity; a well-developed annual and herbaceous (often bulbous) flora is also common.

Native plants often experience a period of summer dormancy, induced by heat and lack of soil moisture, except in some cool, foggy coastal zones.

Frequent summer and autumn fires, brought on by months without rain, serve as a natural means of renewing vegetative growth and of maintaining the health and vitality of the native plant communities.

Soils are generally low in humus, neutral to alkaline in pH, low in biological activity, low in nitrogen and phosphorous, and slow in the decomposition of organic matter; the rugged topography generally leads to a mosaic of old and new soils, with extensive areas of deep alluvial soils (particularly in California), thin soils on slopes due to extensive erosion, and a general susceptibility to erosion, degradation, and desertification.