The tropical climate is the characteristic atmospheric time of the intertropical strip, that is, the region between the tropics of Cancer and Capricorn. It is a warm climate where there are no frosts, since the temperature does not drop below 0 ºC.
However, this condition alters with altitude, since in the intertropical zone there are high mountains where the temperature drops extremely. Another characteristic is the low variation in inter-monthly temperature (annual thermal oscillation), less than the variation between day and night.
Rainfall is variable, from averages of 100 mm per year to 9,000 mm per year, although areas of high humidity predominate. This climate is located in the intertropical region, that is, between the Tropic of Cancer (north of the equator) and that of Capricorn (south of the equator).
The tropical climate covers extensive areas of America, Africa, Asia and Oceania with four subtypes (dry, wet-dry or savanna, humid or monsoon, and rainy or equatorial). Because it is warm and isothermal (temperatures not very variable throughout the year) with high humidity, it promotes great biodiversity.
Tropical rainforests, such as those of the Amazon and Congo, are found in tropical climate zones. These ecosystems are home to a large proportion of the planet’s plant and animal species as well as areas of India, Southeast Asia and Oceania.
Tropical climate characteristics
The tropical climate is characterized by warm temperatures (average annual temperatures above 18ºC). Although according to other authors, the average annual temperature must exceed 20 ºC or even 26 ºC to be considered a tropical climate.
Temperatures above 0 ºC
In this climate there are no temperatures of 0 ºC, therefore there are no frosts and its high temperatures are due to the incidence of solar radiation throughout the year. However, frost or snow can occur in tropical areas, since in these regions there are high mountains.
Variations with altitude
In the mountain ranges, temperatures drop due to the altitude, generating climates similar to temperate and even cold. Although they are not properly temperate or cold climates, since daytime solar radiation is high throughout the year.
Thus, in the high parts of the tropical Andes night frosts and snowfalls occur. The same occurs in the high mountains of tropical Africa such as Kilimanjaro which reaches 5,891.5 m.
In these areas, temperatures rise considerably during the day due to high solar radiation. In this sense, the botanist Vareschi has described the climate of the tropical moor as “an eternal summer in the day and winter at night.”
Duration of day and night
Due to its location in the middle of the planet, the intertropical region presents a balanced duration of the day with the night. In general terms, 12 hours of light and 12 hours of darkness are received throughout the year.
This occurs because the sun’s rays fall vertically on the area ( zenith sun ), which in turn conditions the regularity of temperature variations.
Annual and daily thermal oscillation
The variation of the average temperature throughout the year is low (2 to 5 ºC) and is referred to as an isothermal climate (of the same temperature). Therefore, there are not four periods or climatic seasons, but alternations of dry and rainy seasons, with variable sequences and durations.
In general, closer to the equator, the rainy season is longer and closer to the tropics (Cancer to the north and Capricorn to the south), the dry period increases. Furthermore, the temperature oscillation between day and night becomes greater (10 to 15 ºC) than the inter-monthly oscillation.
In the tropical climate, water precipitates in liquid form, except in the high mountains. However, the amount and frequency of rainfall varies greatly from one place to another in the tropical region.
In areas close to the equator, rainfall reaches about 9,000 mm on average per year, while in other remote areas it only rains 100 mm on average. The latter occurs in arid and semi-arid tropical zones, which are located far from the equator.
Consequently, the relative humidity (water vapor contained in the air) is also variable. Thus, there are areas such as tropical rain forests and high mountain cloud forests, where the relative humidity reaches 80% or more.
Atmospheric pressure and winds
Due to the high temperatures, especially around the equator, the air masses expand and rise, generating areas of low pressure. The free space left by the rising air masses in the middle of the planet makes lower temperature air flow there.
These masses come from the northern and southern latitudes of the tropical zone, in such a way that regular winds are generated. These are the trade winds that come from the northeast in the northern hemisphere and from the southeast in the southern hemisphere.
This confluence of permanent winds from both hemispheres forms updrafts that generate rain clouds. This gives rise to the Intertropical Convergence Zone, which oscillates from north to south depending on the annual incidence of solar rays.
The drastic differences in warming between water and land generated by high tropical temperatures produce another wind phenomenon called the monsoon. This is because as the land warms faster than the water, the air moves from the sea to the continental interior.
These air masses, in turn, carry moisture from the sea, generating precipitation on the continent. Then when the earth cools the process is reversed and there are dry wind flows towards the sea.
The tropical climate develops in the planetary strip between the tropic of Cancer (northern hemisphere) and the tropic of Capricorn (southern hemisphere). This strip then goes from latitude 23º 26 ′ 14 ″ north (Tropic of Cancer) and 23º 26 ′ 17 ″ south latitude (Tropic of Capricorn).
A strip of 204,000 km is formed known as the intertropical zone, through whose center the equatorial line passes. This line or terrestrial equator divides the planet into two hemispheres, the north and the south.
The intertropical zone encompasses large regions of Central America, South America, Africa, Asia, and Oceania. In America it goes from the south of Mexico and the Caribbean area, to the north of Chile, Argentina, Paraguay and part of the south of Brazil.
In Africa, it includes the entire strip of sub-Saharan Africa to central Namibia and Botswana, northern South Africa, part of southern Mozambique and the island of Madagascar. While in Asia it goes from central India to all of Southeast Asia, including the extreme south of China.
Lastly, Oceania includes New Guinea and the rest of Melanesia, northern Australia, Micronesia, and part of Polynesia.
Subtypes of tropical climate
There are various systems for classifying tropical climate subtypes, generally based on the dynamics of rainfall. Thus, for example, Köppen considers a tropical climate to be any humid and rainy area with an average monthly temperature always above 18ºC.
In his system there are three subtypes of tropical climate: very humid (Af jungle), humid (A.M monsoon) and wet-dry (Aw / As sabanero). For Köppen, the dry climate is not part of the tropical climate, considering it a different climate type with two subtypes: semi-arid and arid.
For its part, in the Holdridge system, the tropical climate corresponds to average temperatures never below 24 ºC. This system is not limited to a climatic classification, but defines life zones on the planet.
For this, it takes into account temperature, precipitation and evapotranspiration and defines for the tropical region humidity provinces, which are 8 and range from super-arid to super-humid.
Integrating and simplifying these proposals, the subtypes are defined below: dry, humid-dry or savanna, humid and very humid or rainy.
In this subtype, mean annual temperatures range from 24 to 30 ºC and rainfall is less than 300 mm on an annual average. There is a marked and prolonged dry season, while the rainy season is short.
In the intertropical zone, a dry climate is found in various areas of Mexico, northern South America and northeast Brazil (Caatinga). In Africa, it is located in the strip called the sahel, between the Sahara desert and the savannah.
Wet-dry or savanna
It is a transitional climate between the dry and the monsoon subtype, presenting two seasons of similar duration (dry and rainy) and is typical of the savannas of Africa and tropical America. The average annual temperature is between 20 and 28 ºC, with rains between 800 and 1,800 mm per year.
Humid or monsoon
It is characterized by having two seasons, with the rainy season of great intensity and annual average maximum temperatures between 26 and 32 ºC. Average annual rainfall exceeds 2,000 mm.
It occurs in India, Southeast Asia, West Africa, areas of Central Africa, and Madagascar. As well as in the Gulf of Mexico, Central America, the Caribbean and South America.
Rainy or very humid
It is also known as the equatorial climate, because it occurs mainly near the Earth’s equator. It is also called a tropical jungle climate, since in general it gives rise to this type of plant formation.
In this subtype, rainfall occurs almost all year round and exceeds 2,500 mm, with average temperatures always higher than 27 ºC. It is located in the north of the Amazon basin, in the Congo basin and in Melanesia (New Guinea and adjacent islands).
Due to the optimal temperature and humidity conditions during the year, the regions with a tropical climate have the greatest diversity of vegetation on the planet. The most biodiverse terrestrial ecosystems are found in this type of climate, such as tropical rain forests and cloudy mountain rain forests.
There is a predominance of angiosperms, with little representation of gymnosperms (conifers and others). Due to the high rainfall characteristic of this climate, large rivers develop that feed a variety of ecosystems.
In the tropical climate zone is the Amazon-Orinoco basin, with the largest extension of forests in the world. Similarly, we find the jungles and other ecosystems of the Congo River basin in Africa and the extensive jungles of Southeast Asia.
In the jungles of the Amazon and Guiana region, it is estimated that there are more than 16,000 species of trees. Some are emerging giants above the canopy, such as the Red Angelim (Dinizia excelsa) up to 88 m high, as well as small understory grasses.
In mountain cloud forests there are also tall trees such as the dipper (Gyranthera caribensis) and the rubbers or kills sticks (Ficusspp.). As well as a huge mass of epiphytic and climbing plants developing at all levels of the jungle.
The ecosystems of the high mountains of the tropical Andes, such as the páramo, are also extremely diverse in flora. Many families of plants are unique to the tropical climate or reach their greatest diversity here, such as palms, bromeliads, orchids, malvaceae, and moraceae.
The greatest diversity of fauna is found in tropical climate zones, especially rainforests and savannas. Of the 17 megadiverse countries listed by the Environmental Conservation Monitoring Center, 15 are in areas with a tropical climate.
In the case of the African savannas, they host an enormous diversity of species and large populations, especially of large mammals. However, although less visible, the most diverse animal group in the world and in tropical climates are insects.
Emblematic animals of the tropical climate are the big cats (lion, tiger, leopard, jaguar and others) and primates (gorillas, chimpanzees, orangutans and others). Similarly, most species of snakes, alligators, and crocodiles are from areas with a tropical climate.
Likewise, there is the greatest diversity of birds, where countries like Brazil and Colombia have about two thousand species each.
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