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Cape of Good Hope, Cape Peninsula, Cape Town, South Africa

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Cape of Good Hope, Cape Peninsula, Cape Town, South Africa

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Cape of Good Hope, Cape Peninsula, Cape Town, South Africa

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Kipushi, Democratic Republic of the Congo

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Bokungu, Democratic Republic of the Congo

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Origin

Tropical rainforests represent the oldest major vegetation type still present on the terrestrial Earth. Like all vegetation, however, that of the rainforest continues to evolve and change, so modern tropical rainforests are not identical with rainforests of the geologic past.

Tropical rainforests grow mainly in three regions: the Malesian botanical subkingdom, which extends from Myanmar (Burma) to Fiji and includes the whole of Thailand, Malaysia, Indonesia, the Philippines, Papua New Guinea, the Solomon Islands, and Vanuatu and parts of Indochina and tropical Australia; tropical South and Central America, especially the Amazon basin; and West and Central Africa ( see biogeographic region). Smaller areas of tropical rainforest occur elsewhere in the tropics wherever climate is suitable. The principal areas of tropical deciduous forest (or monsoon forests) are in India, the Myanmar- Vietnam-southern coastal China region, and eastern Brazil, with smaller areas in South and Central America north of the Equator, the West Indies, southeastern Africa, and northern Australia.

The flowering plants ( angiosperms) first evolved and diversified during the Cretaceous Period about 100 million years ago, during which time global climatic conditions were warmer and wetter than those of the present. The vegetation types that evolved were the first tropical rainforests, which blanketed most of Earth's land surfaces at that time. Only later-during the middle of the Paleogene Period, about 40 million years ago-did cooler, drier climates develop, leading to the development across large areas of other vegetation types.

It is no surprise, therefore, to find the greatest diversity of flowering plants today in the tropical rainforests where they first evolved. Of particular interest is the fact that the majority of flowering plants displaying the most primitive characteristics are found in rainforests (especially tropical rainforests) in parts of the Southern Hemisphere, particularly South America, northern Australia and adjacent regions of Southeast Asia, and some larger South Pacific islands. Of the 13 angiosperm families generally recognized as the most primitive, all but two- Magnoliaceae and Winteraceae-are overwhelmingly tropical in their present distribution. Three families-Illiciaceae, Magnoliaceae, and Schisandraceae-are found predominantly in Northern Hemisphere rainforests. Five families-Amborellaceae, Austrobaileyaceae, Degeneriaceae, Eupomatiaceae, and Himantandraceae-are restricted to rainforests in the tropical Australasian region. Members of the Winteraceae are shared between this latter region and South America, those of the Lactoridaceae grow only on the southeast Pacific islands of Juan Fernández, members of the Canellaceae are shared between South America and Africa, and two families- Annonaceae and Myristicaceae-generally occur in tropical regions. This has led some authorities to suggest that the original cradle of angiosperm evolution might lie in Gondwanaland, a supercontinent of the Southern Hemisphere thought to have existed in the Mesozoic Era (252 to 66 million years ago) and consisted of Africa, South America, Australia, peninsular India, and Antarctica. An alternative explanation for this geographic pattern is that in the Southern Hemisphere, especially on islands, there are more refugia-i.e., isolated areas whose climates remained unaltered while those of the surrounding areas changed, enabling archaic life-forms to persist.

The first angiosperms are thought to have been massive, woody plants appropriate for a rainforest habitat. Most of the smaller, more delicate plants that are so widespread in the world today evolved later, ultimately from tropical rainforest ancestors. While it is possible that even earlier forms existed that await discovery, the oldest angiosperm fossils- leaves, wood, fruits, and flowers derived from trees-support the view that the earliest angiosperms were rainforest trees. Further evidence comes from the growth forms of the most primitive surviving angiosperms: all 13 of the most primitive angiosperm families consist of woody plants, most of which are large trees.

As the world climate cooled in the middle of the Cenozoic, it also became drier. This is because cooler temperatures led to a reduction in the rate of evaporation of water from, in particular, the surface of the oceans, which led in turn to less cloud formation and less precipitation. The entire hydrologic cycle slowed, and tropical rainforests-which depend on both warmth and consistently high rainfall-became increasingly restricted to equatorial latitudes. Within those regions rainforests were limited further to coastal and hilly areas where abundant rain still fell at all seasons. In the middle latitudes of both hemispheres, belts of atmospheric high pressure developed. Within these belts, especially in continental interiors, deserts formed ( see desert: Origin). In regions lying between the wet tropics and the deserts, climatic zones developed in which rainfall adequate for luxuriant plant growth was experienced for only a part of the year. In these areas new plant forms evolved from tropical rainforest ancestors to cope with seasonally dry weather, forming tropical deciduous forests. In the drier and more fire-prone places, savannas and tropical grasslands developed.

Retreat of the rainforests was particularly rapid during the period beginning 5,000,000 years ago leading up to and including the Pleistocene Ice Ages, or glacial intervals, that occurred between 2,600,000 and 11,700 years ago. Climates fluctuated throughout this time, forcing vegetation in all parts of the world to repeatedly migrate, by seed dispersal, to reach areas of suitable climate. Not all plants were able to do this equally well because some had less-effective means of seed dispersal than others. Many extinctions resulted. During the most extreme periods (the glacial maxima, when climates were at their coldest and, in most places, also driest), the range of tropical rainforests shrank to its smallest extent, becoming restricted to relatively small refugia. Alternating intervals of climatic amelioration led to repeated range expansion, most recently from the close of the last glacial period about 10,000 years ago. Today large areas of tropical rainforest, such as Amazonia, have developed as a result of this relatively recent expansion. Within them it is possible to recognize "hot spots" of plant and animal diversity that have been interpreted as glacial refugia.

Tropical rainforests today represent a treasure trove of biological heritage, and they also serve as sinks for more than 50 percent of all atmospheric carbon dioxide absorbed by plants annually. They not only retain many primitive plant and animal species but also are communities that exhibit unparalleled biodiversity and a great variety of ecological interactions. The tropical rainforest of Africa was the habitat in which the ancestors of humans evolved, and it is where the nearest surviving human relatives- chimpanzees and gorillas-live still. Tropical rainforests supplied a rich variety of food and other resources to indigenous peoples, who, for the most part, exploited this bounty without degrading the vegetation or reducing its range to any significant degree. However, in some regions a long history of forest burning by the inhabitants is thought to have caused extensive replacement of tropical rainforest and tropical deciduous forest with savanna.

Not until the past century, however, has widespread destruction of tropical forests occurred. Regrettably, tropical rainforests and tropical deciduous forests are now being destroyed at a rapid rate in order to provide resources such as timber and to create land that can be used for other purposes, such as cattle grazing ( see deforestation). Today tropical forests, more than any other ecosystem, are experiencing habitat alteration and species extinction on a greater scale and at a more rapid pace than at any other time in their history-at least since the major extinction event (the K-T extinction) at the end of the Cretaceous Period, some 66 million years ago ( see Sidebar: Status of the World's Tropical Forests).

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Tropical rainforest | Definition, Characteristics, Location, Climate, Animals, Plants, & Facts

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Tropical rainforest, luxuriant forest found in wet tropical uplands and lowlands near the Equator. Tropical rainforests are dominated by broad-leaved trees that form a dense upper canopy and contain a wide array of vegetation and other life. Worldwide, they make up one of Earth's largest biomes (major life zones).

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Congo Rainforest, Kinkenge, Democratic Republic of the Congo

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Congo Rainforest, Kinkenge, Democratic Republic of the Congo

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Congo Rainforest, Kinkenge, Democratic Republic of the Congo

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This article was most recently revised and updated by

Humid subtropical climate, major climate type of the Köppen classification characterized by relatively high temperatures and evenly distributed precipitation throughout the year. This climate type is found on the eastern sides of the continents between 20° and 35° N and S latitude. Although the climate is made up of two subtypes (Cfa and Cwa), the Cfa subtype predominates.

Köppen climate classification map M.C. Peel, B.L. Finlayson, and T.A. McMahon (2007), updated world map of the Köppen-Geiger climate classification, Hydrology and Earth System Sciences, 11, 1633-1644.

In summer, these regions are largely under the influence of moist, maritime airflow from the western side of the subtropical anticyclonic cells over low-latitude ocean waters. Temperatures are high; the warmest months generally average about 27 °C (81 °F), with mean daily maxima from 30 °C to 38 °C (86 °F to 100 °F) and warm, oppressive nights. Summers are usually somewhat wetter than winters, with much of the rainfall coming from convectional thunderstorm activity; tropical cyclones also enhance warm-season rainfall in some regions. The coldest month is usually quite mild (5-12 °C [41-54 °F]), although frosts are not uncommon, and winter precipitation is derived primarily from frontal cyclones along the polar front.

In North America, the spring and early summer seasons, when the front begins its northward return, are notorious for the outbreak of tornadoes associated with frontal thunderstorms along the zone of interaction between tropical and polar air. In eastern and southern Asia, the monsoon influence results in a modified humid subtropical climate (Cwa) that has a clearly defined dry winter when air diverges from the Siberian anticyclone, and the polar front and cyclone paths are deflected around the region. These areas generally lie on the poleward side of tropical monsoon (Am) and tropical wet-dry (Aw) climates and exhibit a somewhat larger annual temperature range than Cfa types. Winters are sunny and rather cool. Annual precipitation totals average about 100 cm (39 inches) but vary from 75 to over 200 cm (30 to 79 inches).

John P. Rafferty, Editor.

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Humid subtropical climate

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Humid subtropical climate, major climate type of the Köppen classification characterized by relatively high temperatures and evenly distributed precipitation throughout the year. This climate type is found on the eastern sides of the continents between 20° and 35° N and S latitude. Although the

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Elephant grass can grow to 15 feet tall in some areas with the tropical savanna climate.

The tropical savanna climate is also called the tropical wet and dry climate. It is the climate experienced in savanna or tropical grassland regions of the world. These places are located near the equator, and they lie between the Southern and the Northern Tropics. The climate dominates many parts of the African continent, the northern region of South America, and parts of Asia such as India. The tropical savanna climate has alternating dry and wet seasons, hence its name. It shares some similar characteristics with the tropical monsoon climate, but it receives less annual rainfall as compared to the tropical monsoon climate. In the Köppen classification, the climate is designated as Aw or As.

Characteristics of the Tropical Savanna Climate

Temperature

Tropical savanna climates are relatively hot since they lie within the tropical latitudes. Throughout the year, mean monthly temperatures soar above 64 °F (18 °C). The dry season in savanna grasslands is cooler than the wet season by a few degrees. During the wet season, temperatures are between 78 to 86 °F (25 - 30 °C). In the dry period of the year, the temperature ranges between 68 to 78 °F (20 - 25° C). Temperatures are higher during the day as compared to nights. The highest temperatures are experienced just before the rainy season, which is October in the southern hemisphere and April in the northern hemisphere.

Precipitation

Precipitation in the tropical savanna climate is mainly in the form of rainfall. On average, this climatic zone receives between 800 and 1,600 millimeters of rain annually. As one moves away from the equator, the mean annual rainfall decreases. During the driest month, precipitation is less than 60 mm. Savanna regions have two seasons, summer and winter. Rain falls mainly in summer. The rains fall from May to September in the northern hemisphere and from October to March in the southern hemisphere.

Winds

The prevailing winds in tropical grasslands are the Trade Winds. They are easterlies, blowing from east to west. These winds have an enormous impact on the rains in this climate zone. For example, rainfall in the savanna decreases from east to west. They are also the cause of the alternating dry and wet seasons. During summer, onshore winds bring rain and in winter, offshore winds keep the savanna region dry. The Trade Winds are strongest in summer.

Variations of the Tropical Savanna Climate

There are four varieties of this climate. The first type has two distinct seasons which last for relatively equal durations. Regions that experience this climate receive the most annual rainfall during the wet season with very little rain falling during the dry period of the year. In the second variation, the dry season is more pronounced and it lasts for seven months or more. The wet season is shorter, lasting for five months or less. This type of savanna climate has two extremes, one that receives just a bit more rainfall than a semi-arid climate, and another that has an extremely rainy wet season. The third type of tropical savanna climate has a short dry season which lasts for five months or less and seven months or more of rainfall. Lastly, there are tropical grassland areas that receive a significant amount of rainfall during the dry season and more rainfall during the wet season. This variation is a bit similar to the tropical monsoon climate but the amount of precipitation during either of the two seasons is less than that of tropical monsoons.

Flora and Fauna in Tropical Savanna Climate

Vegetation

The natural vegetation of savanna regions mainly consists of tall grass and short deciduous trees. Trees such as acacias shed their leaves during the dry period of the year to avoid excessive loss of water to the environment through transpiration. They also tend to have broad trunks which store water to help them survive periods of prolonged drought. On average, the grass grows to a length of between 3 and 6 feet. In true savanna areas, however, it attains a height of 6 to 12 feet, and it is also coarse. In some regions, the elephant grass species may grow to 15 feet tall. Tropical grasslands are moderately green during the rainy seasons but the grass turns yellow and eventually dies down during dry periods. As one moves from the tropical savanna climate into desert regions, the vegetation is dominated by dwarf acacias and scrubs.

Animals

Tropical grasslands are home to thousands of animal species. The African savanna has the greatest diversity of hoofed mammals including giraffes, deer, and hippos which inhabit marshy areas in the grasslands. The ecosystem of tropical savannas consists of two broad categories of animals, herbivores, and carnivores. Carnivorous animals include leopards, lions, tigers, jaguars, jackals, panthers, and hyenas. Herbivorous animals of the savanna comprise antelopes, elephants, rhinos, wildebeest, buffaloes, warthogs, and plains zebra. Antelopes are highly diversified and they include gazelles, impalas, elands, kudus, gerenuks, and oryxes. Kangaroos, rodents, reptile species, beetles, and many termite species also inhabit the tropical grassland areas. Besides wild animals, grassland regions are often inhabited by pastoralist communities who carry out cattle farming.

Distribution of the Tropical Savanna Climate

The African savanna is a belt covering the Sudan Region, East Africa, and the region of southern Africa lying north of the Southern Tropic. In Australia, the climate is prevalent in the northern part of the country stretching from Broome to Townsville. The South American savanna covers two distinct regions. They include the llanos or savannas, which lie north of the equator in the Orinoco valley, and the south central parts of Brazil. Some portions of Central America and parts of the southern region of North America such as Mexico and Florida also experience this climate. In India, the climate covers parts of Telangana, southern Maharashtra, and the northern areas of Karnataka.

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What Are The Characteristics Of A Tropical Savanna Type Of Climate?

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The tropical savanna climate is also called the tropical wet and dry climate. It is the climate experienced in savanna or tropical grassland regions of the world. These places are located near the equator, and they lie between the Southern and the Northern Tropics.

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Atlantic Ocean, Avenue Imam Assili, Asilah, Maroc

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Atlantic Ocean, Avenue Imam Assili, Asilah, Maroc

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Atlantic Ocean, Avenue Imam Assili, Asilah, Maroc

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Arid climates can be found on every continent. They range from hot and dry deserts that see almost no rain to semiarid scrub land where rain falls intermittently. Arid climates are not suitable for most life forms. Plants and animals that make their homes in arid climates have made special adaptations to the environment.

The defining characteristic of an arid climate is a lack of moisture. The soil is dry, the air is dry, and yearly precipitation is very low. A variety of factors combine to steer storms and moisture away from arid regions. In some arid climates, evaporation rates exceed precipitation, leading to a net moisture loss. In the hottest of arid climates, rain may evaporate before it can reach the ground. On the other hand, a torrential downpour may bring a short burst of life.

Arid climates such as the Sahara Desert can be hot all year round with no noticeable seasons. Or they can have hot summers and frigid winters, like the Gobi Desert in Tibet. The Gobi experiences winter temperatures well below freezing. Even the hottest deserts typically have cold nights, because there's little vegetation to retain the day's heat. A traveler exposed to a harsh, arid climate can suffer heatstroke during the day and hypothermia at night.

The leeward or downwind slopes of high mountains are often home to arid climates. When mountains receive the moisture from incoming storm systems, precipitation is abundant on the windward side, leaving the leeward slopes dry. The Gobi Desert in Tibet is a prime example of this phenomenon. The massive peaks of the Himalayas force moisture from the rising air. From the Gobi Plateau, you can see beautiful snow-capped peaks, but rarely does rain fall.

Most of the world's arid climates lie just north and south of the tropical rain forests of the equator. Mountain plateaus are another location where you might find an arid climate. The southwestern corner of the United States, for example, is quite dry and hot. While not technically desert, the continent of Antarctica qualifies as arid. Very little precipitation falls so far south, and all of the region's moisture is locked up in snow and ice.

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Arid climates can be found on every continent. They range from hot and dry deserts that see almost no rain to semiarid scrub land where rain falls intermittently. Arid climates are not suitable for most life forms. Plants and animals that make their homes in arid climates have made special adaptations to the ...

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In the semi-arid climate, summers last longer and are drier than other regions of the world save for deserts, which represent the driest places on Earth. Dew condensation at night -- along with species adaptation -- helps plants and animals thrive in semi-arid regions.

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This article was most recently revised and updated by

Mediterranean climate, major climate type of the Köppen classification characterized by hot, dry summers and cool, wet winters and located between about 30° and 45° latitude north and south of the Equator and on the western sides of the continents. In the Köppen-Geiger-Pohl system, it is divided into the Csa and Csb subtypes.

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. Annual temperature ranges are generally smaller than those found in marine west coast climates, since locations on the western sides of continents are not well positioned to receive the coldest polar air, which develops over land rather than over the ocean. Mediterranean climates also tend to be drier than humid subtropical ones, with precipitation totals ranging from 35 to 90 cm (14 to 35 inches); the lowest amounts occur in interior regions adjacent to the semiarid steppe climates.

Some coastal locations (such as southern California in the western United States) exhibit relatively cool summer conditions and frequent fogs where cold offshore currents prevail. Only in Europe, where the latitude for this climate type fortuitously corresponds to an ocean basin (that of the Mediterranean Sea, from which this climate derives its name), does this climate type extend eastward away from the coast for any significant distance.

letter symbol

1st

2nd

3rd

criterion

¹ In the formulas above, r is average annual precipitation total (mm), and t is average annual temperature (°C). All other temperatures are monthly means (°C), and all other precipitation amounts are mean monthly totals (mm).

² Any climate that satisfies the criteria for designation as a B type is classified as such, irrespective of its other characteristics.

³ The summer half of the year is defined as the months April-September for the Northern Hemisphere and October-March for the Southern Hemisphere.

⁴ Most modern climate schemes consider the role of altitude. The highland zone has been taken from G.T. Trewartha, An Introduction to Climate, 4th ed. (1968).

Data Sources: Adapted from Howard J. Critchfield, General Climatology, 4th ed. (1983), and M.C. Peel, B.L. Finlayson, and T.A. McMahon, "Updated World Map of the Köppen-Geiger Climate Classification," Hydrology and Earth System Sciences, 11:1633-44 (2007).

m

precipitation in driest month less than 60 mm but equal to or greater than 100 - (r/25) ¹

B ²

70% or more of annual precipitation falls in the summer half of the year and r less than 20t + 280, or 70% or more of annual precipitation falls in the winter half of the year and r less than 20t, or neither half of the year has 70% or more of annual precipitation and r less than 20t + 140 ³

H ⁴

temperature and precipitation characteristics highly dependent on traits of adjacent zones and overall elevation-highland climates may occur at any latitude

The Editors of Encyclopaedia Britannica Adam Augustyn.

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Mediterranean climate | Definition, Region, Map, & Facts

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Mediterranean climate, major climate type of the Köppen classification characterized by hot, dry summers and cool, wet winters and located between about 30° and 45° latitude north and south of the Equator and on the western sides of the continents. In the Köppen-Geiger-Pohl system, it is divided into the Csa and Csb subtypes.

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Nile River, Kornish Al Nile, Tahna Al Gabal, Minya, Egypt

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Nile River, Kornish Al Nile, Tahna Al Gabal, Minya, Egypt

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Nile River, Kornish Al Nile, Tahna Al Gabal, Minya, Egypt

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https://www.thousandwonders.net/Atlas+Mountains