The equatorial, hot, wet climate is found between 5° and 10° north and south of the equator. Its greatest extent is found in the lowlands of the Amazon, the Congo, Malaysia and the East Indies. Further away from the equator, the influence of the on-shore Trade Winds gives rise to a modified type of equatorial climate with monsoonal influences. Within the tropics, the equatorial highlands have a distinctively cooler climate, modified by altitude, such as the Cameroon Highlands in Malaysia, the Northern Andes and the Kenyan Highland in East Africa. Fig. 17.1 shows the regions of the world which experience a hot, wet equatorial climate.
1) Temperature: The most outstanding feature of an equatorial climate is its great uniformity of temperature throughout the year. The mean monthly temperatures are always around 27° C (80° F) with very little variation. There is no winter. Cloudiness and heavy precipitation help to moderate the daily temperature, so that even at the equator itself, 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.
Figs. 17.2(a) and 17.2(b) show the rhythm of climate experienced in two different equatorial regions, one on a lowland (Warri, Nigeria) and the other on a highland (Bogota, Colombia) The uniformity in temperature within each region is apparent at once.
Warri has its hottest month with 28°C (82°F) and its coolest month with 26°C (78°F) The annual range is no more than 2°C (4°F). The mean monthly temperatures for Bogota are comparatively low because of its altitudinal differences. It is located in the Andes, 2850 m ( 9350 feet) above sea-level. Its annual range is equally small, 1° C (15°-14°C). Statistics taken from various equatorial stations indicate that the annual range of temperature is small: Freetown 2.5°C, Axim 2.1°C, Singapore 1.3°C and Quito 0.4°C. Over the oceans, the range is even smaller e.g. Jaluit in the Marshall Islands in the Pacific Ocean records a range in temperature of only 0.4°C.
2) Precipitation: Precipitation is heavy, between 1524 mm and 2699 mm (60 inches and 106 inches), and well distributed throughout the year. There is no month without rain, and a distinct dry season, like those of the Savanna or the Tropical Monsoon Climates is absent. Instead, there are two periods of maximum rainfall, April and October, which occur shortly after the equinoxes. Least rain falls at the June and December solstices. The double rainfall peaks coinciding with the equinoxes area characteristic feature of equatorial climates not found in any other type of climate. But this simple pattern may be altered by local conditions. Bogota, Colombia, illustrates the prevailing double rainfall pattern, whereas Warri, Nigeria, has a less distinct double rainfall peak and a more marked dry season.
In West Africa, Freetown (Sierra Leone), Conakry (Guinea) and Bissau (Guinea Bissau) receive most of their rains from the South-West Coast Monsoonal winds between June and November. Kelantan, Malaysia, receives its rainfall from the NorthEast Monsoon at the end of the year and Rangoon, Burma, from the South-West Monsoon between June and September. Further north and south of the equator, particularly in coastal districts open to the influence of the trades, the tendency is towards a monsoonal pattern with the heaviest rainfall coming in the summer months i.e. June and August in the northern hemisphere and December, January and February in the southern hemisphere.
Due to the great heat in the equatorial belt, mornings are bright and sunny. There is much evaporation and convectional air currents are set up, followed by heavy downpours of convectional rain in the afternoons from the towering cumulonimbus clouds.
Thunder and lightning often accompany the torrential showers and the amount of rainfall recorded in one single afternoon may be as much as the deserts receive for the entire year. Besides the convectional rainfall, mountainous regions also experience much orographic or relief rain. In addition, there are some intermittent showers from cyclonic atmosphere disturbances caused by the convergence of air currents in the Doldrums.
The relative humidity is constantly high (over 80 percent), making one feel ‘sticky’ and uncomfortable. The monotonous climate, oppressive and enervating, taxes one’s mental alertness and physical capability, though along the coasts refreshing sea breezes do bring some relief. As a result, most of the white settlers, whose bodies are attuned to cooler and more varied conditions, take the cooler highlands whenever they can.
Equatorial regions support a luxuriant type of dense vegetation – the tropical rain forest because of the very heavy rainfall (over 2032 mm/80inches) and uniformly high temperature (27°C/80°F). In the Amazon lowlands, the forest is so dense and so complete in its vegetational extravagance that a special term, ‘selvas is used. Unlike the savanna mediterranean and temperate climates, the growing season in equatorial regions is not restricted by either drought or cold. Plant growth is continuous throughout the year -seeding, flowering, fruiting and decaying do not take place in a seasonal pattern.
1) A great variety of vegetation: The equatorial vegetation comprises a multitude of evergreen trees that yield tropical hardwood e.g. mahogany, ebony, greenheart, cabinet woods and dyewoods. There are smaller palm trees, climbing plants like the lianas or rattan which may be hundreds of metreslong,andepiphytic and parasitic plants that live on other plants. Under the trees grow a wide variety of creepers, ferns, orchids and lalang.
2) A distinct layer arrangement: 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. All plants struggle upwards for sunlight, resulting in a peculiar layer arrangement. The tallest trees attain a height of 60 m (150 feet).
Their slender trunks pierce skywards with widespread branches at the top. The smaller trees beneath form the next layer and the ground is rooted with ferns and herbaceous plants which can tolerate shade. The undergrowth is sparse as the taller trees cut off most of the sunlight.
3) Multiple species: Unlike the temperate forests, where only a few species occur in a particular area, the trees of the tropical rain forest are not found in pure stands of a single species. It has been estimated that in the Malaysian forest, as many as 490 species of trees may be found in a hectare (200 in an acre) of forest. This has made commercial exploitation of tropical timber a most difficult task. Many of the tropical hardwoods do not float readily on water and this makes haulage an expensive matter. It is therefore not surprising that many tropical countries are timber importers.
4) Forest clearings: Many parts of the virgin tropical rain forests have been cleared either for lumbering or shifting cultivation. When these clearings are abandoned, less luxuriant secondary forests, called belukar in Malaysia, spring up. These are characterized by short trees and very dense undergrowth. In the coastal areas and brackish swamps, Mangrove forests thrive.
Life and Development in the Equatorial Regions
The equatorial regions are generally sparsely populated. In the less accessible forests, some people still live the simple life of growers, hunters and collectors; and in Africa, only the Pygmies, a very small group of remnant people, practise hunting and collecting. But in open forests, more advanced people depend on peasant agriculture, growing food crops for subsistence or for sale, and growing cash crops for export. There are numerous animals, birds and reptiles that can be hunted to serve the needs of the community. The rivers and streams provide a supply of fish. From the forests leaves, fruits, nuts and other forest products can be gathered. Food crops, like cassava (manioc, tapioca), yams, maize and bananas are grown. When the soil is exhausted, the clearing is left to fallow for some years to regain its lost fertility; another area is then cleared for growing crops before the farmers come to use the fallow land again after a few years. This system is known as bush fallow system and it is an efficient way of land management among peasant farmers.
With the coming of the Europeans, many large plantations have been established, especially in Java, Sumatra, Malaysia, West Africa, D.R. Congo and Central America. The climate has proved to be very favourable for the cultivation of certain crops that are highly valued in the industrial West. The most outstanding is natural rubber, called Hevea brasiliensis. Though, it was first discovered in its wild state as para rubber in the Amazon basin, it has since been transplanted to other parts of the equatorial lands and is grown very profitably on large estates. Malaysia and Indonesia are the leading producers, each accounting for more than a third of the world production. The home country, Brazil, exports practically no natural rubber. The problems of tree diseases and the lack of commercial organization of the Indians in the Amazon lowlands have brought about this unexpected ‘shift’ of rubber cultivation. Liberia is a major grower and exporter of natural rubber which forms an important source of income for the country. Most of the rubber plantations are owned by the Firestone Rubber Company. Nigeria is another producer of rubber in West Africa. Most of Nigeria’s rubber is grown by government statutory corporations and companies in Edo, Ondo, Oyo, Ogun, Akwa Ibom and Cross River States.
Another tropical crop that has achieved an amazing success is cocoa. It is cultivated most extensively in West Africa, bordering the Gulf of Guinea. The three most important producers are Cote d’Ivoire, Ghana and Nigeria. There is a keen demand for the crop and acreages are rapidly on the increase. Most of the crop leaves West Africa for Europe or North America for the cocoa and chocolate industry. From the same area another crop, oil palm, has done equally well, and many countries outside Africa have now taken to its cultivation. Other crops that have been found suitable to the hot, wet equatorial climate and are extensively cultivated are coconuts, sugar, coffee, tea, tobacco, spices, cinchona, bananas, pineapples and sago.
Factors affecting the Development of Equatorial Regions
1) Equatorial climate and health: With its excessive heat, high humidity and heavy rainfall, some people assert that the equatorial climate impairs or retards man’s efficiency and productivity and slows down economic progress and development. Malaria and yellow-fever are prevalent. However, nowadays malaria eradication schemes are in progress in most tropical areas and vaccines have been developed to counteract other diseases.
2) Prevalence of bacteria and insect pests: The hot, wet climate which stimulates rapid plant growth also encourages the spread of insects and pests. As germs and bacteria are more easily transmitted through moist air, equatorial conditions are ideal for the survival of such organisms. Insects and pests not only spread diseases but are injurious to crops. They plague both men and animals.
3) Jungle hinders development and maintenance: The forest is so luxuriant that it is quite a problem to clear a small patch of it and even more difficult to maintain it. Tall grass and thick undergrowth spring up as soon as the shade trees are cut,and unless they are weeded at regular intervals, they may choke crops and overwhelm estates. In the same way, roads and railways which have been constructed through the equatorial lands have to cut through forests, dense thickets and swamps in many cases. Once completed, they have to be maintained at a high cost. Many remote parts of the Amazon basin, Zaire and Borneo are without modern communication lines. The rivers form the only natural highways.
4) Rapid deterioration of tropical soil: It is a misconception that tropical soils are rich. In its virgin, untouched state, due to heavy leaf-fall and the decomposition of leaves by bacteria, a thick mantle of humus makes the soil fairly fertile. This is clear from the shifting cultivators heavy croppings in their newly cleared lands. But once the humus is used and the natural vegetative cover is removed, the torrential downpours soon wash out most of the soil nutrients. The soil deteriorates rapidly with subsequent soil erosion and soil impoverishment. One may quote the Indonesian island of Java as an exception, because of its rich volcanic ashes and the energetic local people. The bush fallow or land rotational system which is common among peasant farmers of West Africa has been found to be a useful method of conserving and regenerating the soil. In Malaysia, Singapore and eastern Brazil, much progress has also been made in the development of the tropical lands through systematic planning and the will of the people to succeed.
5) Difficulties in lumbering and livestock farming: As mentioned earlier, though the tropics have great potential in timber resources, commercial extraction is difficult. The trees do not occur in homogenous stands, there are no frozen surfaces to facilitate logging and the tropical hardwoods are sometimes too heavy to float on the rivers, even if these flow in the desired directions. But in spite of this difficulty, there are many valuable timbers that are obtained from the high forest, which form an important item in the export of the countries where they are produced. For instance, in West Africa, exporting timber is an important item of international trade. In Cote d’Ivoire, in particular, timber accounts for over 20 percent of the country’s total export value. Other countries in West Africa with considerable development of their timber resources include Nigeria and Ghana, with numerous sawmills. Most of the timber is exported as logs, some as sawn timber and some as plywood. In Nigeria, plywood is manufactured at Sapele, and at Epe, near Lagos. There are wood factories also at Calabar and Ondo.
Livestock farming is greatly handicapped by an absence of meadow grass, even on the highlands. The few animals like bullocks or buffaloes are kept mainly as beasts of burden. Their yield in milk or beef is well below those of the cattle in the temperate grasslands. The grass is so tall and coarse that it is not nutritious.
In Africa, domesticated animals are attacked by tse-tse flies which cause trypanosomiasis (sleeping sickness), a deadly disease. Foot-rot and neuropneumonia are other common animal diseases.