GC Leong Summary: The Hot, Wet Equatorial Climate | Geography for UPSC CSE PDF Download

Distribution

• The equatorial climate, characterized by its hot and wet conditions, is typically found between 5° and 10° north and south of the equator.
• This climate is most prominently observed in regions such as the lowlands of the Amazon, the Congo, Malaysia, and the East Indies.
• As one moves further from the equator, the influence of the on-shore Trade Winds leads to a modified version of the equatorial climate, which includes monsoonal effects.
• Within the tropics, the equatorial highlands experience a notably cooler climate due to the effects of altitude. Examples of such highland areas include the Cameron Highlands in Malaysia, the Northern Andes, and the Kenyan Highlands in East Africa.

Climate 

• The equatorial climate is characterized by a remarkable consistency in temperature throughout the year. Mean monthly temperatures hover around 80°F, with minimal variation. There is no winter season. The presence of clouds and heavy rainfall helps to moderate daily temperatures, making the climate at the equator more bearable. Additionally, regular land and sea breezes contribute to this stable climate. 
• Small Diurnal and Annual Range: The diurnal (daily) and annual temperature ranges are both small. For example, Kuala Lumpur experiences a range of 80°F in its hottest month to 78°F in its coolest month, with an annual variation of no more than 2°F. 
• Temperature in High Altitudes: Cities like Bogota, located in the Andes at an altitude of 8,730 feet above sea level, have lower mean monthly temperatures, although their annual range is also small, about 2°F (from 59°F to 57°F ). The dotted line in temperature graphs often represents how these temperatures would compare at sea level.
• Examples of Temperature Uniformity: Various equatorial stations show small annual temperature ranges, such as Singapore (2.3°F ), Djakarta (1.8°F ), Quito (0.7°F ), and Colombo (3.2°F ). Over the oceans, the temperature range is even smaller, as seen in Jaluit in the Marshall Islands, which records a range of only 0.8°F.

Precipitation

• Amount and Distribution: Precipitation in equatorial regions is heavy, ranging between 60 inches to 100 inches annually, and is well-distributed throughout the year. There is no month without rain, and a distinct dry season, as seen in Savanna or Tropical Monsoon Climates, is absent. 
• Peaks of Rainfall: There are two periods of maximum rainfall, occurring in April and October, shortly after the equinoxes. Conversely, the least rainfall is observed during the June and December solstices. This double peak of rainfall is a distinctive feature of equatorial climates, setting them apart from other climate types. 
• Local Variations: Local conditions can disrupt this typical pattern. For instance, Kola Bharu in Kelantan receives most of its rainfall from the North-East Monsoon at the end of the year, while Rangoon in Burma gets its heaviest rainfall from the South-West Monsoon between June and September. 
• Influence of Latitude: As one moves further north and south of the equator, especially in coastal areas exposed to trade winds, the climate tends to adopt a monsoonal pattern. This results in heavier rainfall during the summer months, such as June, July, and August in the northern hemisphere, and December, January, and February in the southern hemisphere. 
• Afternoon Rainfall: Due to the intense heat in the equatorial region, mornings are typically bright and sunny, leading to significant evaporation and the formation of convectional air currents. This is followed by heavy afternoon downpours of convectional rain, characterized by towering cumulonimbus clouds. These storms are often accompanied by thunder and lightning, with the amount of rainfall in a single afternoon sometimes exceeding the annual total for deserts. 
• Orographic Rain: Mountainous regions within the equatorial belt also experience substantial orographic or relief rain. Additionally, there are intermittent showers caused by cyclonic disturbances resulting from the convergence of air currents in the Doldrums. 
• Humidity and Comfort: The relative humidity in equatorial regions is consistently high, over 80 percent, which can make the environment feel sticky and uncomfortable. This monotonous climate, being oppressive and draining, can affect mental alertness and physical capability. However, coastal areas benefit from refreshing sea breezes that provide some relief. 

Equatorial Vegetation

• The equatorial regions, with their high temperatures and abundant rainfall, support a lush type of vegetation known as the tropical rain forest.
• In places like the Amazon lowlands, the forest is so dense and diverse that a special term, "selva," is used to describe it.
• Unlike temperate regions, the growing season in equatorial areas is year-round. Activities like seeding, flowering, fruiting, and decaying do not follow a seasonal pattern. This means that some trees may be in flower while others nearby are bearing fruit. There is no drought or cold to hinder growth at any time of the year.

The characteristic features of the equatorial vegetation include:

1. Variety of Vegetation: The equatorial region is home to a wide variety of evergreen trees that produce tropical hardwoods such as mahogany, ebony, greenheart, cabinet woods, and dyewoods. There are also smaller palm trees, climbing plants like lianas or rattan, which can be hundreds of feet long, and epiphytic and parasitic plants that live on other plants. Under the trees, there is a diverse range of ferns, orchids, and lalang.
2. Layer Arrangement: From above, the tropical rain forest looks like a thick canopy of foliage, interrupted only by large rivers or cleared areas for cultivation. All plants compete for sunlight, resulting in a unique layer structure over 150 feet tall. The slender trunks of taller trees reach up with wide-spread branches at the top. Beneath them, smaller trees form the next layer, and the ground is covered with ferns and herbaceous plants that can tolerate shade. Because the trees block most of the sunlight, the undergrowth is not very dense.
3. Multiple Species: Unlike temperate forests where a few species dominate, tropical rain forests have a mix of many tree species. For example, in the Malaysian jungle, up to 200 tree species can be found in a single acre. This diversity makes commercial timber extraction challenging. Many tropical hardwoods do not float well on water, making transportation expensive. As a result, many tropical countries end up importing timber.
4. Forest Clearings: Virgin tropical rain forests have been cleared in many areas for logging or shifting cultivation. When these clearings are left alone, less dense secondary forests, known as "belukar" in Malaysia, grow back. These secondary forests are characterized by short trees and very dense undergrowth.

Life and Development in the Equatorial Regions

• Population and Lifestyle: The equatorial regions are usually not very crowded. In the dense forests, the most basic communities survive by hunting and gathering, while more advanced groups practice shifting cultivation.
• Abundance of Food: There is so much food available that people don’t have to worry much about their next meal. These areas are rich in animals, birds, and reptiles that can be hunted for food. The rivers and streams are full of fish, which people catch by spearing or trapping. From the forest, they collect leaves, fruits, nuts, and other products.
• Specific Practices: For example, in the Amazon basin, indigenous tribes collect wild rubber. In the Congo Basin, the Pygmies gather nuts, and in the jungles of Malaysia, the Orang Asli make various cane products to sell to people in nearby villages and towns.
• Shifting Cultivation: In the clearings made for shifting cultivation, crops such as manioc (tapioca), yams, maize, bananas, and groundnuts are planted. Once the soil becomes less fertile, the area is abandoned, and the community moves on to a new plot of land.
• Growth of Cash Crops: This practice is evolving, and plantations are being established, particularly in places like Java, Sumatra, Malaysia, West Africa, and Central America. The climate in these regions is very suitable for growing certain crops that are highly valued in industrialized countries.
• Natural Rubber: The most notable crop is natural rubber, scientifically known as hevea brasiliensis. Although it was originally found in the Amazon basin, where it is called Para rubber, it has been successfully transplanted to other equatorial regions and is now grown profitably on large estates. Malaysia and Indonesia are the top producers of natural rubber, each contributing over a third of global production. In contrast, Brazil, the crop’s home country, exports very little rubber. This shift in production is due to issues like tree diseases in the Amazon and the lack of commercial organization among the indigenous people there.
• Cocoa Production: Another tropical crop that has seen remarkable success is cocoa, which is primarily grown in West Africa, especially along the Gulf of Guinea. Ghana and Nigeria are the leading producers of cocoa, which is in high demand. The acreage devoted to cocoa cultivation is rapidly increasing, with most of the harvest being exported to Europe or North America for the cocoa and chocolate industry.
• Oil Palm and Other Crops: Alongside cocoa, oil palm has also flourished in West Africa, with many countries outside Africa now adopting its cultivation. Other crops that are well-suited to the hot, wet equatorial climate and are widely grown include coconuts, sugar, coffee, tea, tobacco, spices, cinchona, bananas, pineapples, and sago.

Factors Affecting the Development of Equatorial Regions1. Equatorial Climate and Health

• In the equatorial regions, the combination of extreme heat and high humidity poses serious challenges to human physical and mental health.
• The harsh conditions lead to excessive sweating, resulting in a loss of vitality and energy.
• People in these regions are at risk of heat-related illnesses such as sunstroke, as well as diseases like malaria and yellow fever.
• These factors significantly reduce their capacity for work and weaken their resistance to illnesses.
• Without proper sanitation, both physical and mental health are adversely affected.
• However, efforts such as malaria eradication programs and the development of vaccines for other diseases are being implemented to improve health conditions in tropical areas.

2. Prevalence of Bacteria and Insect Pests

• The hot and humid climate of equatorial regions not only promotes rapid plant growth but also facilitates the spread of insects and pests.
• Bacteria and germs thrive in moist air, making equatorial conditions ideal for their survival.
• Insects and pests pose a threat to both humans and animals by spreading diseases and damaging crops.
• The prevalence of these harmful organisms is a significant factor affecting development in these regions.

3. Jungle Hindering Development and Maintenance

• The dense jungle in equatorial regions presents a formidable challenge for development and maintenance.
• Clearing even a small patch of jungle is a difficult task, and once cleared, the area needs constant maintenance.
• Tall grasses and thick undergrowth quickly regenerate after trees are cut, and if not regularly managed, they can choke crops and overtake estates.
• Additionally, constructing and maintaining roads and railways through equatorial lands involves cutting through forests, thickets, and swamps, with the added challenges of encountering wild animals, poisonous snakes, and insects.
• The maintenance of these infrastructure projects is costly and requires ongoing effort.

4. Rapid Deterioration of Tropical Soil

• There is a common misconception that tropical soils are inherently rich.
• In their natural state, tropical soils benefit from a thick layer of humus created by heavy leaf-fall and the decomposition of leaves by bacteria, making them relatively fertile.
• This is evident from the heavy crop yields of shifting cultivators in newly cleared areas.
• However, once the humus is depleted and the natural vegetation is removed, the soil nutrients are quickly washed away by heavy rainfall.
• This leads to rapid soil deterioration, erosion, and impoverishment.
• Exceptions like the Indonesian island of Java, known for its rich volcanic soil and active local population, exist.
• In places like Malaysia, Singapore, and eastern Brazil, significant progress in tropical land development has been achieved through systematic planning and determination.

5. Difficulties in Lumbering and Livestock Farming

• Despite the potential for timber resources in the tropics, commercial extraction is fraught with difficulties. 
• Tropical trees are not found in uniform stands, and the absence of frozen surfaces complicates logging. 
• Additionally, tropical hardwoods are sometimes difficult to transport via rivers, even when they flow in the desired directions. 
• Livestock farming in equatorial regions is hindered by the lack of nutritious meadow grass, even in highland areas. 
• Animals such as bullocks and buffaloes are primarily used as working animals, and their milk and meat production is significantly lower than that of cattle in temperate grasslands. 
• The grass in these regions is often tall and coarse, making it unpalatable and lacking in nutrients. 
• In some areas of Africa, domesticated animals are further threatened by tsetse flies, which transmit nagana, a fatal disease.