Short essay on Subtropical Dry-summer Climate (Cs) or Mediterranean Climate

The Mediterranean climate is characterized by a dry summer, a mild humid winter and abundant sunshine-about 90 percent of the possible sunshine in summer and 50 to 60 per cent even during the rainy winter season.

Because of these characteristics the Mediterranean climate is considered as resort climate of the world.

Location:

Mediterranean climates are found between 30° and 40° N and S latitudes on the western sides of the continents. These climates are found in five regions of the world: the borderlands of the Mediterranean Sea (north of the Mediterranean Sea from Portugal to Turkey and beyond in the Iranian Highlands; the southern borderland includes Morocco, northern Algeria, and Tunisia, and north of Bengasi in Libya): the central and southern California cost in the United States of America; central Chile; the Cape-town area of South Africa; and southern and southwestern coasts of Australia.

Mediterranean climate is limited to the above-mentioned small areas of the world. In fact, this type of enjoyable climate occupies only 1.7 percent of the earth’s land area.

The main characteristics of this climate are determined by the ocean winds. That is why Mediterranean climate is not found far inland.

However, the most extensive regions with this type of climate are found around the Mediterranean Sea where the marine influence penetrates between Africa and Europe. Besides, the Mediterranean Sea itself has a moderating effect on the inland climate.

In central Chile and California the oceanic influence is confined by coastal mountains. Areas on the leeward side of these mountains are dry because of the rain-shadow effect.

In case of Africa and Australia, Mediterranean climate occupies the southern and southwestern extremities instead of the west coast. This is only because these continents have limited extent in the Mediterranean latitudes.

The most important controlling factor that produces Mediterranean type of climate is its location between the latitudes of 30° and 40° and S.

During winter when the pressure and wind belts move towards the equator by a few degrees, the regions with Mediterranean type of climate come under the influence of the westerlies and the polar fronts which bring cyclonic storms and precipitation.

As summer approaches, the subtropical high-pressure belt migrates pole-ward, and the Mediterranean latitudes then experience the dry, subsiding and diverging air of the high-pressure system.

Thus, because of the seasonal migration of the wind belts towards north and south, the Mediterranean regions have a dry tropical climate during summer and humid climate of the middle latitudes during winter.

Temperature:

The average temperature of the coldest month in Mediterranean climate is usually between 4.4° and 10°C, and of the hottest month between 21°C and 27°C. The mean annual ranges are between 11⁰ and 17°C.

The mean annual ranges of temperature are less than those of the moist cool temperate climates and greater than those of the dry tropical climates. The annual range of temperature, however increases with distance from the sea: at San Francisco it is only 5.5°C, but at Sacramento 15°C, at Naples 16°C, but at Rome 18°C.

Stations that are located farther away from the oceanic influence record highest summer temperatures, whereas coastal locations have very low summer temperatures because of the presence of the cold ocean currents which parallel the western coasts in these latitudes.

But even at coastal locations where the cold currents are not so strong, the summer temperatures are usually higher. Because of warm winter, the annual range of temperature is nowhere very large.

However, the inland stations are characterized by hotter summers and cooler winters. On the contrary, the Mediterranean coastal climates show the moderating influence of the oceans, and are much cooler in summer and warmer in winter.

It may be noted that the annual range of temperature at Red Bluff, an inland station in California is 20°C, while at San Francisco located on the coast; it is only 7.2°C.

Around the coasts of the Mediterranean Sea, where cold currents are conspicuous by their absence, summer temperatures are much higher than those on oceanic coasts. It is because of this that average temperature for the month of July in Athens, Rome and Istanbul are usually more than 21°C.

In the Mediterranean climate, sub-tropical high pressure systems cause the summer temperatures to be higher. Because of clear weather, the average summer temperatures in lower- latitude and inland stations are more than 21° or even 27°C.

Day time maximum temperatures may reach 32° to 38°C. Day time maximum temperatures may reach 32° to 38°C.

Clear skies, almost vertical rays of the sun and the low relative humidity are the contributory factors in raising the temperatures like the dry climates, because of rapid loss of heat by nocturnal radiation the night temperatures record a considerable fall.

Thus, the diurnal range of temperature is considerably large, particularly in the drier Mediterranean climates. The daily range for Sacramento in the Great valley for the month of July was recorded 20.3°C.

Frost is usually rare in the Mediterranean climate. But there are occasional frosts which prove to be most injurious to crops sensitive to cold.

Since valleys and depressions which are filled with dense cold air are prone to have freezing or even subfreezing temperatures in winter, the sensitive crops like citrus are planted on hill slopes.

However, sometimes the Mediterranean cultivators have to incur huge losses due to occasional frosts. In fact, it is the rarity of frosts which tempts the farmers to grow many less hardy varieties of fruits and vegetables. Even one night’s frost proves fatal to such sensitive crops.

Precipitation:

The Mediterranean climate has rainy winter and dry summer. This climate receives moderate to scanty precipitation so that it is labelled as sub-humid. The average annual precipitation is usually between 35 cm and 75 cm. About 75 percent of the total precipitation is received during winter.

Since there is almost complete drought in summer, it is called the dry- summer subtropical climate. Because the Mediterranean climate is located between the dry climates found equator-ward and humid mesothermal climate pole-ward.

It is natural that the amount of precipitation goes on increasing from its equator-ward to pole-ward margins. Besides, there is also an increase in precipitation from the inland to coastal locations.

In the Northern Hemisphere, the Mediterranean climate receives most of its precipitation between December and March, while in the Southern Hemisphere the rainy season lasts from May to August.

During winter the Mediterranean regions are occupied by the west wind belt, so precipitation results mainly from the temperate cyclones moving with the westerlies.

In coastal regions backed by mountains, orographic precipitation is common. At times, this type of precipitation may cause floods and mud flows. Thunder-showers are uncommon in this type of climate.

In mountainous regions orographic lifting of moisture- laden air masses may produce thunderstorms. There is considerable variation of the total amount of precipitation from place to place on account of the site characteristics.

Since the Mediterranean climate gets most of its precipitation during the winter months, even moderate to scanty rainfall is more effective because of the lower temperature.

The rainy season in this type of climate is characterized by many days of fine and sunny weather. In the Mediterranean climate, snowfall is a rare phenomenon except in highland areas.

The mountains present in this climatic region have abundant snowfall during winter. The snowfall of the Mediterranean mountains is a valuable source of water for irrigation and hydroelectric power.

Natural vegetation:

Because of the extreme summer drought in larger parts of the Mediterranean climate, much of the natural vegetation is sclerophyllus (hard-leaved) and drought resistant.

Much of the natural vegetation consists of plants those posses’ moisture-conserving devices such as tough surfaces, shiny thick leaves that resist moisture loss, and deep roots to be able to suck up soil-moisture.

Where the precipitation amount is large enough such as in the moist depressions and the shady north sides of the hills, dense woodlands are found. They consist of pine, oak, cedar, madrone, walnut and chestnut trees.

Besides, where the drought is not so severe, deciduous oak may be found. Cork oak is also found in these woodlands, and it is considered to be a valuable asset to the wine industry of the Mediterranean climate. In Western Australia, there are vast stands of eucalyptus trees.

Low, scrubby bushes growing together in a thick tangle form the most characteristic natural vegetation of the Mediterranean climate.

In the California, these scrubs are called chaparrals which are often threatened by fire. Chaparral acts as a check against soil erosion during the periods of rains. This scrub is called maqui in France, mattoral in Chile and mallee in Australia.

In areas of lower rainfall and poor soil, there are low growing evergreens like rosemary, myrtle, laurel and arbutus with a few taller trees here and there.

During the rainy season there is the vegetative cover of lush green grasses which get parched up with the approach of the dry summer. With the approach of winter the grasses cover the hillsides giving them a green tinge.

Since most of the precipitation occurs during the low sun period when temperatures are lower, grass is uncommon in this type of climate.

That is why there is a dearth of cattle and abundance of goats in the Mediterranean climate. That is the reason why milk, butter and meat are not in plenty there. People naturally take more of beans, olive oil and fruit juice etc.

There is abundance of drought resistant fruits like olive or irrigated circus fruits. Long summer drought encourages fruit growing. Olive, figs and vine are the native fruits of the Mediterranean climates which are well adapted to drought conditions. However, peaches, oranges, lemons etc. are grown on irrigated lands.