Mediterranean Climate (Warm Temperate Western Margin Climate)
- Mediterranean climate is found between the 30o- 45oN-S latitudes & gets its name from the climate found around the Mediterranean Sea.
- The basic cause of this type of climate is shifting of the wind belts with summers – warm to hot, and winters – cool but mild.
- These regions have also been called ‘winter-rain & summer dry’
- The Mediterranean biome is divided intofive floristic biome subtypes, according to the various floristic realms into which each fall –
|Mediterranean||Areas around Mediterranean sea|
|Californian||Around San Francisco|
|Chilean||Central Chile (South America)|
|Capensic||Cape Town, Africa|
|Australian||Southern & Western Australia|
- Though the area around Mediterranean Sea has the great extent of this type of agriculture, the best developed form of this peculiar type of climate is infact found in central Chile.
- 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.
Dry, warm summer with off shore trade winds
- The summer months have relatively higher temperature (~ 20* – 30* C), with highest temp. recorded are away from the coast & in more eastern continental Mediterranean.
- In summers, when the sun is overhead at the Tropic of Cancer, the belt of influence of westerlies is shifted a little polewards.
- Rain bearing winds, therefore, are not likely to reach Mediterranean lands.
- The prevailing trade winds are off shore; as all of the Mediterranean region lies on the western margin of the continents except large portions of the Mediterranean Basin; and all the regions are situated along the coast of oceans or the Mediterranean Sea, therefore the air is dry, heated & is of low relative humidity with practically no rains.
- Days are excessively warm in the interiors & prolonged droughts are common, with areas at coast getting relief from moderating effects of the seas.
Mild, Rainy winter with on shore Westerlies
- The Mediterranean lands receive most of their precipitation in winters (~65-70 %), when the westerlies shift equatorward, with average temp. in winters approx. 10 – 12*C
- In the northern hemisphere, the prevailing on shore westerlies brings much cyclonic rain from from the Atlantic to the countries bordering Mediterranean Sea.
- The mean annual rainfall is approx. 70 cm, which differs greatly from place to place, depending on the relief, continentality & passing of the cyclones.
- Mediterranean regions are often backed by mountains along the coasts which provide an effective barrier to oncoming westerlies.
- As a result, Portuguese coast is much wetter than eastern Spain & much heavier precipitation has been recorded in highlands of windward slopes facing the westerlies.
- The steep hills of the eastern Adriatic are the rainiest part of Europe.
- Rain comes in heavy showers but only on few days, with bright sunny periods between them; mostly from Sep – Feb, with peak at October.
- Though the downpour is infrequent, they are often very torrential & in mountainous regions, cause destructive floods.
Local Winds around Mediterranean Sea
- Many local winds, some hot, others cold are common around the Mediterranean Sea due to the varied topography of the region
- High Alps in the north, Sahara desert in south, Continental interiors in east & open Atlantic on west, give rise to great differences in temperature, pressure & precipitation
- The passing cyclones from the Atlantic, the anticyclones from the north & cold air masses from the continental interior are often interrupted by relief features, resulting in birth of local winds around the Mediterranean
- This is a hot, dry, dusty wind which originates in the Sahara desert
- Though it may occur at any time of the year, but most frequent in springs & lasts only for few days
- Sirocco blows outward from the desert interior to the cooler Mediterranean Sea
- It is usually associated with depressions from Atlantic passing from the coast to eastward inlands
- After crossing the Mediterranean Sea, Sirocco is slightly cooled by absorption of water vapour but still remains hot & dry with a temperature of over 40*C
- It withers crops & vegetation; and the damage is particularly serious when it comes at the times during which Vines & Olives are in blossom
- Sirocco is also known as blood rain due to the red dust it carries from Sahara Desert
- It is so prominent that it is known by different local names such as –
|Khamsin||Egypt & Malta|
- In Adriatic & Aegean Sea, this hot wind, better known as Gharbi, gathers much moisture, causing fog, dew & rains
Fohn Wind & Chinook Wind
- Both the Fohn & Chinook winds are local hot & dry winds experienced on the leeward side of the mountains when descending air become compresses with increased pressure.
- Fohn wind is experienced in the valleys of northern Alps, particularly in Switzerland in spring.
- Chinook winds are experienced on the eastern slopes of the Rockies in USA & Canada in winters.
- While descending, most of the moisture of the wind is lost & hence it becomes dry & hot, which may lead to rise in temperature of leeward side.
- In North America, it is called Chinook which means the snow eater, as it melts the snow & causes avalanches.
- It has blessings too, it enhances the growth of crops & fruits & thaws the snow covered pastures by raising temperature of the region quite quickly.
- In contrast to Sirocco, Mistral is a cold wind from the north, rushing down the Rhone valley (France) in violent gusts between 40 – 80 miles / hour.
- Velocity of Mistral is intensified by the funneling effect in the valley between Alps & Central Massif (France).
- In winters, when the Mistral is most frequent, the temperature of the wind may be below freezing point, though the sky may be clear & cloudless.
- Therefore, as a protective measure, many of the houses & orchards of Rhone valley & Riviera have thick rows of trees & hedges planted to shield them from Mistral.
- A similar type of cold north-easterly wind experienced along the Adriatic coast is called Bora
- Like the Mistral, it is caused by a difference in pressure between continental Europe & Mediterranean
- Usually occur in winter, when the atmospheric pressure over continental Europe is higher than that of Mediterranean
- This dry, icy wind is even more violent than the Mistral & speeds of over 100 mph have been recorded
- During strong Boras, ships may be blown aground & agricultural land ruined.
Natural vegetation of Mediterranean Region
- In a land with half the year dry, one cannot expect the natural vegetation to be luxuriant.
- In the Mediterranean area, the natural vegetation is xerophyte, or drought resistant
- Consists of cypress, cork oak, scrub evergreen, olive, and low bushes
- The native vegetation of Mediterranean climate lands must be adapted to survive long, hot summer droughts and prolonged wet periods in winter.
- Trees with small broad leaves are widely spread & never very tall
- The absence of shade is a distinct feature of Mediterranean lands.
- Soil is often reddish in colour, indicating high iron content.
- The low amounts of rain in this region result in little leaching of the soil, and the humus content is low from lack of leaf fall.
- Growth is slow in cooler & wetter season, even though more rain falls in winter; & long summer drought checks the growth
- Thus growth is almost restricted to autumn & spring, when the temperature is higher & moisture is just sufficient.
Mediterranean Evergreen Forests
- Open Woodlands with evergreen oaks, found only in climatically most favored regions with rainfall well over 70 cm viz. Spain & Portugal.
- In Australia, eucalyptus forests replace the evergreen oaks
- Trees are normally low, even stunted with massive trunks
- Have deeply fissured barks, small leathery leaves & wide spread root system in search of water
Evergreen Coniferous Trees
- Include various kinds of pines, cedars & cypresses with needle shaped leaves & tall, straight trunks.
- They appear more on cooler highlands & where droughts are less severe.
Bushes & Shrubs
- Perhaps the most dominant type of Mediterranean vegetation as summers are so dry & hot that in places, forests give place to short, evergreen shrubs & bushes, which are scattered in clamps & are often thorny.
- Are generally drought & heat resistant & have developed various strategies of growth & usage of available water during the dry period
- They are usually known by different names in different regions such as –
|Mallee and kwongan||Australia|
- Conditions in Mediterranean do not suit grass, as most of the rain comes in cool season when growth is slow.
- Slow growing vegetation, which cannot replenish their foliage readily, & without deep penetrating roots, is least suitable here.
- Even if grass do survive, they are wiry & bunchy and are not suitable for animal farming; Cattle rearing is thus unimportant in Mediterranean.
- Grass which is replaced by certain drought resistant varieties of shrubs & flowering herbs, can however support sheep or goats.
- As a result of above mentioned facts, animal fats are unimportant here & chief cooking oil is obtained from olives; Dairy products are net import items.
Agricultural developments in Mediterranean
- Mediterranean lands are famous for citrus fruits cultivation, Cereal growing & Wine making majorly.
- Mediterranean lands are also known as world’s orchard lands
- Wide varieties of citrus fruits such as oranges, lemons, limes, citrons & grapefruit are grown.
- The fruit trees have long roots to draw water from considerable depths during the long summer drought; in exceptionally dry areas, irrigation helps to relieve the lack of moisture.
- The thick leathery skin of citrus fruits prevents excessive transpiration & the long, sunny summer enables the fruits to be ripened & harvested.
- The Mediterranean lands account for 70 % of world’s export of citrus fruits.
- The olive tree is probably the most typical of all Mediterranean cultivated vegetation
- As Olive tree is so hard & long rooted that it can survive even on very poor limestone soils, with less than 25 cm of annual rainfall.
- Besides olives, many nut trees like chestnuts, walnuts, hazelnuts & almonds are grown, picked as fruits or for chocolate industry.
- Other important fruits are peaches, apricots, pears, plums, cherries & figs.
- Cereals are by far the most important cultivated crops in Mediterranean, with wheat as the leading food crop, used for bread making
- Barley is the next most important cereal
- Other food products like spaghetti, vermicelli & macaroni
- Farmers usually sow the seeds in autumn, so that they can grow & germinate steadily with coming winter rain; by springs there is still sufficient moisture for wheat to mature
- Other important food crops cultivated here are rice, vegetables especially beans, & flowers, for local market
- A little cotton & tobacco are also grown
- The mountain pastures, with cool climate, support a fur sheep, goats & sometimes cattle with widespread practice of Transhumance
- A specialty of the Mediterranean countries
- The regions bordering Mediterranean Sea account for 3/4th of the total world’s production of wine
- The long, sunny summer allow grapes to ripen with almost 85 % of grapes produced go into wine production