A Mediterranean climate is a climate characterised by hot, dry summers and mild to cool, relatively wet winters. In the Köppen climate classification it is generally represented by Csa or Csb, with Csa referring to hot summer Mediterranean conditions and Csb to warm summer conditions. The climate is named after the Mediterranean Basin, where the type is widespread, but it also occurs in several other regions on western sides of continents at approximately subtropical to warm temperate latitudes. Its defining seasonal contrast is the combination of summer drought and winter rainfall.
The Mediterranean seasonal cycle results largely from the movement of subtropical high pressure and the mid latitude westerlies. During summer, subtropical high pressure expands poleward and produces descending air that suppresses cloud formation and rainfall. During winter, the subtropical high pressure belt retreats, allowing the westerlies and mid latitude cyclones to reach Mediterranean climate regions. These storms bring much of the annual precipitation. This reversal creates the distinctive dry summer and wet winter pattern. The precise timing and strength of these systems vary geographically and from year to year.
Mediterranean climates are strongly influenced by their position on western continental margins and by nearby oceans. Coastal waters moderate temperature, while offshore currents can influence atmospheric stability and moisture. Mountains can create sharp contrasts between windward and leeward areas and can modify both rainfall and temperature. In California, for example, the Pacific Ocean and coastal mountain systems influence the climate, while central Chile is similarly affected by the Pacific and Andes. In southern Australia and South Africa, regional oceanic and atmospheric conditions produce analogous seasonal patterns.
Summers in Mediterranean climates are generally sunny, warm or hot and dry. Clear skies increase solar heating, while descending air suppresses convection and rainfall. Winters are wetter because frontal systems and cyclones become more frequent. Winter temperatures are moderated in coastal regions, although inland or elevated areas can experience frost and occasional snow. Annual rainfall can be moderate rather than extremely high, but the concentration of precipitation into winter means that plants experience severe seasonal water stress during summer.
Mediterranean vegetation is adapted to recurring summer drought, heat and fire. Common vegetation includes evergreen shrubs, sclerophyllous plants, drought tolerant trees, grasses and seasonal herbs. Leaves may be small, tough, waxy or otherwise adapted to reduce water loss. Fire is a major ecological process in many Mediterranean ecosystems, and numerous plants have adaptations allowing them to survive or regenerate after burning. Human land use has transformed much of the original vegetation through agriculture, grazing, urbanisation and forestry.
Agriculture is strongly influenced by the seasonal climate. Winter rainfall allows crops to grow during the cooler moist period, while summer irrigation may be required for water intensive crops. Grapes, olives, citrus fruits, wheat and various horticultural crops are important in Mediterranean climate regions, although the specific agricultural pattern differs by location. Reservoirs and groundwater are often important because rainfall is scarce during the main growing season for many crops. Drought, wildfire and water scarcity are major environmental constraints, particularly in densely populated coastal areas.
Mediterranean climates occur around the Mediterranean Sea and in regions including central Chile, coastal California, the Cape region of South Africa and parts of southern and southwestern Australia. These regions are geographically separated but share broadly comparable seasonal atmospheric conditions. They do not have identical climates because latitude, elevation, ocean currents, topography and continentality differ. The term Mediterranean climate therefore identifies a climatic pattern rather than implying that all such regions have identical temperatures, rainfall totals or ecosystems.
Mediterranean climate is easily distinguished from oceanic climate because oceanic climates generally receive precipitation throughout the year and lack the pronounced summer drought characteristic of Mediterranean conditions. It also differs from humid subtropical climates, which often have substantial warm season rainfall rather than a strongly dry summer. The defining feature is seasonal water availability rather than simply mild winters or hot summers. Mediterranean climates are particularly important in studies of drought, wildfire, water management, agriculture and ecosystem adaptation because their ecosystems have evolved under predictable but intense summer moisture stress.
