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Geography - Climatology - Rainforest Climate (Tropical Evergreen Climate)
                                                                                                    December 23, 2018


Rainforest Climate (Tropical Evergreen Climate)

Koeppen’s scheme Of Classification Of Climate

  • The most widely used classification of climate is the empirical climate classification scheme developed by V. Koeppen. [empirical: verifiable by observation or experience rather than theory or pure logic][when dropped, stone falls to the ground – logic. Drop a stone to confirm that it falls to the ground – empirical]
  • Koeppen identified a close relationship between the distribution of vegetation and climate. He selected certain values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.
  • Koeppen recognized five major climatic groups, four of them are based on temperature and one on precipitation.
  • The capital letters : A, C, D and E delineate humid climates and B dry climates.
  • The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics.
  • The seasons of dryness are indicated by the small letters : f, m, w and s, where f corresponds to no dry season, m – monsoon climate, w – winter dry season and s – summer dry season.
  • The small letters a, b, c and d refer to the degree of severity of temperature.
  • The B – Dry Climates are subdivided using the capital letters S for steppe or semi-arid and W for deserts.

Koeppen’s Climatic regions Koeppen’s Climate groups Koeppen’s Classification Of Climatic regions Koeppen’s scheme Of Classification Of Climate

Group A : Tropical Humid Climates

  • Tropical humid climates exist between Tropic of Cancer and Tropic of Capricorn.

  • The sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (INTCZ) make the climate hot and humid.

  • Annual range of temperature is very low and annual rainfall is high.

  • The tropical group is divided into three types, namely

  1. Af – Tropical wet climate;

  2. Am – Tropical monsoon climate;

  3. Aw – Tropical wet and dry climate.

ITCZ summer - winter

Tropical Wet Climate (Af)

  • Also known as ‘The Hot, Wet Equatorial Climate’, ‘Equatorial Rainforest Climate’.

  • The regions are generally referred as ‘Equatorial Rainforests’, ‘Equatorial Evergreen Forests’, ‘Tropical Moist Broadleaf Forest’, ‘Lowland Equatorial Evergreen Rainforest’.

Equatorial Rainforest Climate

Distribution

  • Mostly between 5° N and S of Equator. [little or no Coriolis Force == no tropical cyclones]

  • Its greatest extent is found in the lowlands of the Amazon, the Congo, Malaysia and the East Indies.

Equatorial Rainforest distribution

Equatorial Climate

  • Dominated by Maritime Tropical air masses.

Temperature

  • Temperature is uniform throughout the year.

  • The mean monthly temperatures are always around 27° C with very little variation.

  • There is no winter. [Typical to Equatorial Rainforest Climate]

  • Cloudiness and heavy precipitation moderate the daily temperature.

  • Regular land and sea breezes assist in maintaining a truly equable climate.

  • The diurnal range of temperature is small, and so is the annual range.

Precipitation

  • Precipitation is heavy and well distributed throughout the year.

  • Annual average is always above 150 cm. In some regions the annual average may be as high as 250 – 300 cm.

  • There is no month without rain (distinct dry season is absent). The monthly average is above 6 cm most of the times.

  • There are two periods of maximum rainfall, April and October. [shortly after the equinox]. Least rain fall occurs in June and December [solstice].

  • The double rainfall peaks coinciding with the equinoxes are a characteristic feature of equatorial climates not found in any other type of climate.

  • There is much evaporation and convectional air currents are set up, followed by heavy thunderstorms in the afternoons.

Climate Graphs

Equatorial Rainforest climate graph-samoa-indonesia

Equatorial Vegetation

  • High temperature and abundant rainfall support a luxuriant tropical rain forest.

  • In the Amazon lowlands, the forest is so dense that it is called ‘selvas’. [selvas: A dense tropical rainforest usually having a cloud cover (dense canopy)]

  • Unlike the temperate regions, the growing season here is all the year round-seeding, flowering, fruiting and decaying do not take place in a seasonal pattern.

  • The equatorial vegetation comprises a multitude of evergreen trees that yield tropical hardwood, e.g. mahogany, ebony, dyewoods etc.

  • Many parts of the tropical rain forests have been cleared either for lumbering or shifting cultivation.

  • In the coastal areas and brackish swamps, mangrove forests thrive.

Canopy

  • From the air, the tropical rain forest appears like a thick canopy of foliage, broken only where it is crossed by large rivers or cleared for cultivation.

Canopy-equatorial rainforests

  • All plants struggle upwards (most ephiphytes) for sunlight resulting in a peculiar layer arrangement.

Epiphyte: An epiphyte is a plant that grows harmlessly upon another plant (such as a tree) and derives its moisture and nutrients from the air, rain, and sometimes from debris accumulating around it.

Epiphyte-rainforests

  • The tallest trees attain a height close to 50 m.

  • The smaller trees beneath form the next layer.

  • The ground is rooted with ferns and herbaceous plants which can tolerate shade.

  • Because the trees cut out most of the sunlight the undergrowth is not dense.

Multiple species

In spite of dense forests, countries in equatorial regions are net importers of timber. Comment.

  • Though the tropics have great potential in timber resources, commercial extraction is difficult.

  • Multiple species of trees occur in a particular area (trees do not occur in homogenous stands or pure stands) making commercial exploitation a difficult task.

  • Many of the tropical hardwoods (very heavy) do not float readily on water and this makes transportation an expensive matter.

  • It is therefore not surprising that many tropical countries are net timber importers.

Life and Economy

Agriculture

  • The forests are sparsely populated.

  • In the forests most primitive people live as hunter gatherers and the more advanced ones practice shifting cultivation.

  • Food is abundantly available. People generally don’t stock food for the next day.

Commercial

  1. In the Amazon basin the Indian tribes collect wild rubber,

  2. in the Congo Basin the Pygmies gather nuts and

  3. in the jungles of Malaysia the Orang Asli make all sorts of cane products and sell them to people in villages and towns. [The names of the tribes come under Social Geography – Prelims]

Shifting Cultivation or Slash and Burn Cultivation.

  • This type of cultivation is followed in many parts of the world where dense forests are common [In India, North-East is known for this type of cultivation].

  • Tribes cut the trees in a plot, burn them and cultivate the plot till the fertility is exhausted.

  • Once the fertility is exhausted, the clearing is abandoned and they move on to a new plot. Such farming practices are becoming more and more widespread even among backward tribes.

  • In the clearings for shifting cultivation, crops like manioc (tapioca), maize, bananas and groundnuts are grown.

Plantation Boom in Rainforests

  • With the coming of the Europeans, many large plantations have been established, especially in Java, Sumatra, Malaysia, West Africa and Central America.

  • The climate is very Favourable for the cultivation of certain crops that are highly valued in the industrial West. The most important is natural rubber.

  • Malaysia and Indonesia are the leading producers. The home country, Brazil exports practically no natural rubber.

  • Cocoa is another important crop which is cultivated in West Africa, bordering the Gulf of Guinea. The two most important producers are Ghana and Nigeria. All the cocoa here goes into American and European chocolate industry.

  • From the same area another crop, oil palm, has done equally well and many countries like Indonesia have now taken to its cultivation.

  • Other important crops include coconuts, sugar, coffee (Brazil), tea, tobacco, spices, etc.

  • The plantations resulted in the destruction of nearly half of equatorial forests.

Plantation Boom-palm plantation indonesia

Plantations

Regions

Palm

Malaysia, Indonesia

Sugarcane

Brazil

Coffee

Brazil

Rubber

Malaysia, Indonesia

Cocoa

Ghana, Nigeria

Factors Affecting the Development of Equatorial Regions

Equatorial climate and health

  • Excessive heat (sun-stroke) and high humidity creates serious physical and mental handicaps.

  • High humidity feeds many tropical diseases such as malaria and yellow-fever.

  • Communicable diseases are rampant as germs and bacteria are transmitted through moist air.

  • Insects and pests not only spread diseases but are injurious to crops.

Jungle hinders development

  • The construction of roads and railways is a risky business as workers are exposed to wild animals, poisonous snakes, insects and most importantly tropical diseases.

  • Once completed, they have to be maintained at a high cost.

Rapid deterioration of tropical soil

Why does restoration of lost forests take decades in equatorial regions?

  • The fertility of top soil in rainforest regions is very poor. Torrential downpours wash out most of the top soil nutrients [leaching == percolation and draining way of nutrients due to rain water action].

  • The soil deteriorates rapidly with subsequent soil erosion and soil impoverishment.

  • It takes decades to replenish the soil of lost nutrients.

  • So a seed doesn’t usually germinate and even if it does, its development is hindered due to little availability of sunlight.

  • Lalang (tall grass) and thick undergrowth spring up as soon as the trees are cut. They choke the restoration of forests.

  • Indonesian island of Java is an exception because of its rich volcanic ashes.

Difficulties in livestock farming

  • Livestock farming is greatly handicapped by an absence of meadow grass. The grass is so tall and coarse that it is not nutritious.

  • The few animals like buffaloes are kept mainly for domestic use. Their yield in milk or beef is well below those of the cattle in the temperate grasslands.

  • In Africa, domesticated animals are attacked by tsetse flies that cause ngana, a deadly disease.

Mineral resources

  • Gold, copper, diamonds, and other precious metals and gemstones are important resources that are found in rainforests around the world.

  • Extracting these natural resources is a destructive activity that damages the rainforest ecosystem.

  • Examples are gold mining in the Brazilian and Peruvian Amazon, rare earth mining in the Congo, and gold and copper mining in Indonesia and Papua New Guinea.

  • Some of the world’s most promising oil and gas deposits lie deep in tropical rainforests. Oil and gas development often takes a heavy toll on the environment and local people (This happens in Ecuador).

  • More than 70 percent of the Peruvian Amazon is now under concession for oil and gas.