Most large, historic cities of the Mediterranean basin lie within Mediterranean climatic zones, including Algiers, Athens, Beirut, Izmir, Jerusalem, Marseille, Naples, Rome, Tunis, and Valencia. Major cities with Mediterranean climates outside of the Mediterranean basin include Adelaide, Cape Town, Casablanca, Dushanbe, Los Angeles, Lisbon, Perth, San Francisco, Santiago and Victoria.
Under Trewartha's modified K│ppen climate classification, the two major requirements for a Cs climate are revised. Under Trewartha's system, at least eight months must have average temperatures of 10 └C (50 └F) or higher (subtropical), and the average annual precipitation must not exceed 900 mm (35 in). Thus, under this system, many Csb zones in the K│ppen system become Do (temperate oceanic), and the rare Csc zones become Eo (subpolar oceanic), with only the classic dry-summer to warm winter, low annual rainfall locations included in the Mediterranean type climate.
During summer, regions of Mediterranean climate are strongly influenced by the subtropical ridge which keeps atmospheric conditions very dry with minimal cloud coverage. In some areas, such as coastal California, the cold current has a stabilizing effect on the surrounding air, further reducing the chances for rain, but often causing thick layers of marine fog that usually evaporates by mid-day. Similar to desert climates, in many Mediterranean climates there is a strong diurnal character to daily temperatures in the warm summer months due to strong heating during the day from sunlight and rapid cooling at night.
The Mediterranean forests, woodlands, and scrub biome is closely associated with Mediterranean climate zones, as are unique freshwater communities. Particularly distinctive of the climate are sclerophyll shrublands, called maquis in the Mediterranean Basin, chaparral in California, matorral in Chile, fynbos in South Africa, and mallee and kwongan shrublands in Australia. Aquatic communities in Mediterranean climate regions are adapted to a yearly cycle in which abiotic (environmental) controls of stream populations and community structure dominate during floods, biotic components (e.g. competition and predation) controls become increasingly important as the discharge declines, and environmental controls regain dominance as environmental conditions become very harsh (i.e. hot and dry); as a result, these communities are well suited to recover from droughts, floods, and fires. Aquatic organisms in these regions show distinct long-term patterns in structure and function, and are also highly sensitive to the effects of climate change.
Much native vegetation in Mediterranean climate area valleys have been cleared for agriculture. In places such as the Sacramento Valley and Oxnard Plain in California, draining marshes and estuaries combined with supplemental irrigation has led to a century of intensive agriculture. Much of the Overberg in the southern Cape of South Africa, once covered with renosterveld, has likewise been largely converted to agriculture, mainly wheat. In hillside and mountainous areas, away from urban sprawl, ecosystems and habitats of native vegetation are more sustained.