Mediterranean climate

Short description: Type of climate

A Mediterranean climate (/ˌmɛdɪtəˈreɪniən/ MED-ih-tə-RAY-nee-ən), also called a dry summer climate, described by Köppen and Trewartha as Cs, is a temperate climate type that occurs in the lower mid-latitudes (normally 30 to 45 north and south latitude). Such climates typically have dry summers and wet winters, with summer conditions being hot and winter conditions typically being mild. These weather conditions are typically experienced in the majority of Mediterranean-climate regions and countries, but remain highly dependent on proximity to the ocean, elevation, and geographical location.

The dry summer climate is found throughout the warmer middle latitudes, affecting almost exclusively the western portions of continents in relative proximity to the coast. The climate type's name is in reference to the coastal regions of the Mediterranean Sea, which mostly share this type of climate, but it can also be found in the Atlantic portions of Iberia and Northwest Africa, the Pacific portions of the United States and Chile, extreme west areas of Argentina, the southwest tip of South Africa, parts of Southwest and South Australia, and parts of Central Asia. They tend to be found in proximity (both poleward and near the coast) of desert and semi-arid climates, and equatorward of oceanic climates.

Mediterranean climate zones are typically located along the western coasts of landmasses, between roughly 30 and 45 degrees north or south of the equator. The main cause of Mediterranean, or dry summer, climate is the subtropical ridge, which extends towards the pole of the hemisphere in question during the summer and migrates towards the equator during the winter. This is due to the seasonal poleward-equatorward variations of temperatures.[1]

The resulting vegetation of Mediterranean climates are the garrigue or maquis in the European Mediterranean Basin, the chaparral in California, the fynbos in South Africa, the mallee in Australia, and the matorral in Chile. Areas with this climate are also where the so-called "Mediterranean trinity" of major agricultural crops have traditionally been successfully grown (wheat, grapes and olives). As a result, these regions are notable for their high-quality wines, grapeseed/olive oils, and bread products.[2]

## Contents

* 1 Köppen climate classification
* 2 Precipitation
* 3 Temperature
* 4 Mediterranean biome
* 5 References

## Köppen climate classification

Continental Portugal has a clear contrast between the cool to warm (Csb) and hot (Csa) summers. Map of mediterranean climate in europe, showing Csa (Csa) and Csb (Csb) compared.

Under the Köppen climate classification, "hot dry-summer" climates (classified as Csa) and "cool dry-summer" climates (classified as Csb) are often referred to as just "Mediterranean". Under the Köppen climate system, the first letter indicates the climate group (in this case temperate climates). Temperate climates or "C" zones average temperature above 0 °C (32 °F) (or −3 °C (27 °F)), but below 18 °C (64 °F), in their coolest months. The second letter indicates the precipitation pattern ("s" represents dry summers). Köppen has defined a dry summer month as a month with less than 30 mm (1.2 in) of precipitation and as a month within the high-sun months of April to September, in the case of the Northern Hemisphere and October to March, in the case of the Southern Hemisphere, and it also must contain exactly or less than one-third that of the wettest winter month. Some, however, use a 40 mm (1.6 in) level.[3][4] The third letter indicates the degree of summer heat: "a" represents an average temperature in the warmest month above 22 °C (72 °F), while "b" indicates the average temperature in the warmest month below 22 °C (72 °F). There is a "c" with 3 or less months' average temperature above 10 °C (50 °F), but this climate is rare and is very isolated.[3]

Under the Köppen classification, dry-summer climates (Csa, Csb) usually occur on the western sides of continents. Csb zones in the Köppen system include areas normally not associated with Mediterranean climates but with Oceanic climates, such as much of the Pacific Northwest, much of southern Chile, parts of west-central Argentina, parts of New Zealand, and parts of northwestern Spain (Galicia).[5] Additional highland areas in the subtropics also meet Cs requirements, though they, too, are not normally associated with Mediterranean climates. The same goes for a number of oceanic islands such as Madeira, the Juan Fernández Islands, the western part of the Canary Islands, and the eastern part of the Azores.[3]

Under Trewartha's modified Köppen 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), as well as satisfying Köppen's precipitation requirements.

## Precipitation

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“  | Chile has four months of winter, no more, and in them, except when there is a quarter moon, when it rains one or two days, all the other days have such a beautiful sunshine that it is not necessary to resort to fire. The summer is so temperate, with delicious airs, that man can go all day under the sun.  | ”

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— Pedro de Valdivia to Charles V, Holy Roman Emperor

Poleward extension and expansion of the subtropical anticyclone over the oceans bring subsiding air to the region in summer, with clear skies and high temperatures. When the anticyclone moves Equator-ward in winter, it is replaced by traveling, frontal cyclones with their attendant precipitation.[6]

During summer, regions of the 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 ocean 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 evaporate 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 solar heating during the day from sunlight and rapid cooling at night.

In winter, the subtropical ridge migrates towards the equator and leaves the area, making rainfall much more likely. As a result, areas with this climate receive almost all of their precipitation during their winter and spring seasons, and may go anywhere from four to six months during the summer and early fall without having any significant precipitation. In the lower latitudes, precipitation typically decreases during both the winter and summer months. Toward the polar latitudes, total moisture levels generally increase; for example, the Mediterranean climate in Southern Europe tends to experience more rainfall. Rainfall in Southern Europe is also more evenly distributed throughout the year, while in places such as Southern California, the summer is nearly or completely dry. In areas where steppe climates are found, the overall precipitation pattern may still resemble that of Mediterranean climates, though with drier conditions.

Irregularity of the rainfall, which can vary considerably from year to year, accentuates the droughts of the Mediterranean climate. Rain does not fall evenly, nor does the rain arrive at the same time or within the same intervals. In Gibraltar, for instance, rain starts falling nearly half a season earlier than at the Dead Sea. In Palestine no rain at all falls in summer but early rains may come in autumn.[7]

## Temperature

Aegean Sea of Ölüdeniz, Turkey

The majority of the regions with Mediterranean climates have relatively mild winters and very warm summers. However, winter and summer temperatures can vary greatly between different regions with a Mediterranean climate. For instance, in the case of winters, Funchal experiences mild to warm temperatures in the winter, with frost and snowfall almost unknown,[8] whereas Tashkent has cold winters with annual frosts and snowfall;[9] or, to consider summer, Seville experiences rather high temperatures in that season.[10] In contrast, San Francisco has cool summers with daily highs around 21 °C (70 °F)[11] due to the continuous upwelling of cold subsurface waters along the coast.

Because most regions with a Mediterranean climate are near large bodies of water, temperatures are generally moderate, with a comparatively small range of temperatures between the winter low and summer high unlike (the relatively rare) dry-summer humid continental climates (although the daily diurnal range of temperature during the summer is large due to dry and clear conditions, except along the immediate coastlines). Temperatures during winter only occasionally fall below the freezing point and snow is generally seldom seen. Summer temperatures can be cool to very hot, depending on the distance from a large body of water, elevation, and latitude, among other factors. Strong winds from inland desert regions can sometimes boost summer temperatures up, quickly increasing the risk of wildfires. Notable exceptions to the usual proximity from bodies of water, thus featuring extremely high summer temperatures and cooler winters, include south-eastern Turkey and northern Iraq (Urfa, Erbil), surrounded by hot deserts to the south and mountains to the north. Those places routinely experience summer daily means of over 30 °C (86 °F) and daily highs above 40 °C (104 °F), while receiving enough rainfall in winter not to fall into arid or semi-arid classifications.[12]

As in every climatologic domain, the highland locations of the Mediterranean domain can present cooler temperatures in the summer and winter than the lowland areas, temperatures which can sometimes prohibit the growth of typical cold-sensitive Mediterranean plants. Some Spanish authors opt to use the term 'continental Mediterranean climate' (Clima Mediterráneo Continentalizado) for some regions with lower temperatures in winter than the coastal areas,[13] but Köppen's Cs zones show no distinction as long as winter temperature means stay above freezing.

Additionally, the temperature and rainfall pattern for a Csa or even a Csb climate can exist as a microclimate in some high-elevation locations adjacent to a rare tropical As (tropical savanna climate with dry summers, typically in a rainshadow region, as in Hawaii). These have a favourable climate, with mild wet winters and fairly warm, dry summers.

## Mediterranean biome

The Ionian Sea, view from the island Lefkada, Greece Makarska Riviera in Dalmatia, Croatia The coastal Mediterranean region of Costa Brava, Catalonia, Spain

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 flood 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.[14] Aquatic organisms in these regions show distinct long-term patterns in their structure and function,[15] and are also highly sensitive to the recent effects of climate change.[1][2]

## References

1. ↑ 1.0 1.1 Lawrence, J.E.; K.B. Lunde; R.D. Mazor; L.A. Bêche; E.P. McElravy; V.H. Resh (2010). "Long-Term Macroinvertebrate Responses to Climate Change: Implications for Biological Assessment in Mediterranean-Climate Streams". Journal of the North American Benthological Society 29 (4): 1424–1440. doi:10.1899/09-178.1.
2. ↑ 2.0 2.1 Filipe, A.F.; J.E. Lawrence; N. Bonada (November 2013). "Vulnerability of Biota in Mediterranean Streams to Climate Change: A Synthesis of Ecological Responses and Conservation Challenges". Hydrobiologia 719: 331–351. doi:10.1007/s10750-012-1244-4.
3. ↑ 3.0 3.1 3.2 Kottek, Markus; Grieser, Jürgen; Beck, Christoph; Rudolf, Bruno; Rube, Franz (June 2006). "World Map of the Köppen-Geiger climate classification updated". Meteorologische Zeitschrift 15 (3): 259–263. doi:10.1127/0941-2948/2006/0130. Bibcode: 2006MetZe..15..259K. http://www.schweizerbart.de/resources/downloads/paper_free/55034.pdf. Retrieved 27 February 2011.
4. ↑ Peel, M. C.; Finlayson, B. L.; McMahon, T. A. (2007). "Updated world map of the Köppen-Geiger climate classification". Hydrology and Earth System Sciences 4 (2): 439–473. doi:10.5194/hessd-4-439-2007. http://www.hydrol-earth-syst-sci-discuss.net/4/439/2007/hessd-4-439-2007.pdf. Retrieved 27 February 2011.
5. ↑ Peel, M. C.; Finlayson, B. L.; McMahon, T. A. (2007). "Updated world map of the Köppen-Geiger climate classification". Hydrology and Earth System Sciences 11 (5): 1633–1644. doi:10.5194/hess-11-1633-2007. Bibcode: 2007HESS...11.1633P. http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.html. Retrieved 27 February 2011.
6. ↑ "Medittranean climate Definition, Region, Map, & Facts". Encyclopædia Britannica. https://www.britannica.com/science/Mediterranean-climate. Retrieved 2023-08-01.
7. ↑ Gildemeister, Heidi. "What is a medittranean climate?". Mediterranean Garden Society. https://www.mediterraneangardensociety.org/climate.html.
8. ↑ "World Weather Information Service – Funchal(monthly averages for the 30-year period 1961-1990)". WMO. https://worldweather.wmo.int/en/city.html?cityId=5.
9. ↑ "Климатические таблицы. Данные для Ташкента" (in Russian). Weather and Climate. http://www.pogodaiklimat.ru/climate.php?id=38457.
10. ↑ "Valores climatológicos normales. Sevilla Aeropuerto". AEMET. https://www.aemet.es/es/serviciosclimaticos/datosclimatologicos/valoresclimatologicos?l=5783&k=and.
11. ↑ "World Weather Information Service – San Francisco (monthly averages for the 30-year period 1981-2010)". WMO. https://worldweather.wmo.int/en/city.html?cityId=272.
12. ↑ "İllerimize Ait Genel İstatistik Verileri: Sanliurfa" (in Turkish). Meteoroloji Genel Müdürlüğü. https://www.mgm.gov.tr/veridegerlendirme/il-ve-ilceler-istatistik.aspx?k=A&m=SANLIURFA.
13. ↑ "España a Través de los Mapas". http://www.ign.es/espmap/graficos_clima_bach/Clima_Graf_05.htm.
14. ↑ Gasith, A. and V.H. Resh (1999). "Streams in Mediterranean Climate Regions: Abiotic Influences and Biotic Responses to Predictable Seasonal Events". Annu. Rev. Ecol. Syst. 30 (1): 51–81. doi:10.1146/annurev.ecolsys.30.1.51. Bibcode: 1999AnRES..30...51G.
15. ↑ Resh, V.H.; L.A. Bêche; J.E. Lawrence; R.D. Mazor; E.P. McElravy; A.H. Purcell; S.M. Carlson (2013). "Long-term Population and Community Patterns of Benthic Macroinvertebrates and Fishes in Northern California Mediterranean-climate Streams". Journal of the North American Benthological Society 719 (1): 93–118. doi:10.1007/s10750-012-1373-9. Bibcode: 2013HyBio.719...93R.

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