Short essay on Tropical Wet-and-Dry Climate (Aw) or Savanna Climate

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Location:

The tropical savanna type of climate is typically located between 5° and 20° latitudes on either side of the equator. This type of climate occupies the transitional regions between the tropical rain-forest and the semi-arid steppe (BS) climates.

The savanna’s typical location places this climatic region in an intermediate position between the rain- producing intertropical convergence and the rain-suppressing subtropical high-pressure systems.

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Because of the seasonal shifting of the pressure and wind belts, the areas lying between 5° and 15° latitudes are under the influence of the ITC and doldrums during summer, while during winter there is preponderance of the trade winds and the subtropical anticyclones. That is why the savanna type of climate has rainy summer and dry winter.

The pole-ward boundary of this climatic region is formed by the polar limits of migration of the ITC, whereas its equator-ward limits are the equator-ward limits of the drought-producing subtropical anticyclones. Towards the eastern side of a continent it is bounded by the humid subtropical climate (China type) of the temperate zone.

The most extensive areas of savanna climate are found in Latin America (the Llanos of the Orinocco Valley including Colombia and Venezuela, the Guiana Highlands and the Campos of Brazil).

In Africa there are vast areas of savanna climate on either side of the tropical rainforest climatic region.

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South of the Congo Basin, the savanna climatic region is called the weld which extends almost from coast to coast including the southern part of Zaire, Angola, Zambia, Mozambique, Tanzania, Uganda, central Rhodesia and central and south-western Malagasy.

North of the Congo Basin savanna climate is found in the extensive Sudan area. Besides, central Nigeria, southern Kenya and Uganda, Central African Republic, Cameroon, Central Nigeria, Dahomey, Togo, Ghana, the Ivory Coast and eastern Guinea have savanna type of climate.

Other representative areas with this climate are found in the south and Southeast Asia and northern Australia.

Temperature:

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Since most of the representative areas with savanna or tropical wet-and-dry climate are located between latitudes 5°-10° and 15°-20°, the mid-day sun is never far from the overhead position and there is little difference in the length of days and nights in different parts of the year.

The temperatures are, therefore, constantly high, the annual average varying from 24°C to 27°C. In respect of temperature, there is very little difference between the savanna and the equatorial climates.

The annual range of temperature in the savanna is, however, greater than that in the equatorial regions. It is generally over 3° but not more than 8°. The increased distance from the equator is the main reason for slightly greater annual range of temperature.

Winters those are generally dry and cloudless record lower temperatures, whereas during the summer, just before the rainy season, higher temperatures are recorded.

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This is another reason which accounts for the relatively larger annual range of temperature in the savanna climate.

Precipitation:

Total annual average precipitation may vary from 100 to 150 cm. Much of the rain falls during summer. But the total annual rainfall is variable.

Because of the transitional location of this climate between the tropical wet or monsoon and the steppe climates, the precipitation varies greatly within this climatic region.

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The amount of rainfall on its pole-ward margins is much less than on the equator-ward margins. Generally the total amount of rains decreases towards the pole-ward margins situated very close to the BS climate.

The precipitation is characteristically seasonal in character:

The seasonal distribution of rainfall is, in fact, very complex. During winter, the savanna climate as a result of the migration of the wind belt comes under the influence of the subtropical high-pressure system so that this region is dry.

The pole-ward margins are invaded by the dry, dust-laden winds blowing out from the tropical hot deserts. These winds are called the harmattan south of the Sahara, and khamsin in Egypt. The climate becomes as dry as the B climate.

During summer, the savanna type climate experiences tropical rainforest type climate when the air becomes humid and numerous thunderstorms are produced giving heavy rainfall. Sudan, for example, receives convectional showers as well as heavy rainfall from the thunderstorms.

The rainfall which begins in March continues to increase in amount until July or August, when the ITC is located at the farthest point from the equator.

With the retreat of ITC towards the south during the low sun period, the amount of rainfall starts decreasing, so that by October or November this climatic belt is completely dry. The subsiding stable air masses of the subtropical high-pressure systems dominate.

Natural vegetation:

The tropical wet-and-dry climate is called savanna after its typical vegetation i.e. grasslands dotted with scattered trees and bushes that can survive the drought season. Mostly the trees are deciduous and lose their leaves during the dry season to prevent moisture loss through transpiration.

The trees have longer roots so that they can avail of the water in the soil during the dry season. Most of the trees in the savanna region are fire-resistant.

Near the equator-ward margins, there are higher grasses and the trees are taller and closely spaced. Towards the arid margins the grasses are shorter and the heights of the trees diminish and they are more and more scattered.

Animal life:

There is such a large variety of animals in the savanna region that the African savannas are called the zoological gardens for larger tropical mammals. These regions have animals like the elephant, giraffe, zebra, rhinoceros and antelope.

These animals are herbivores, i.e. plant eaters. Many varieties of carnivores, i.e. flesh eaters, are also found in the savanna grasslands.

They include the lions, leopards and tigers. Besides, wild dogs, jackals and wolves and hyena are also found. In the wetter regions nearer the equator, the birds, insects and climbing animals resemble those of the tropical rainforest climate.

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