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 (ITCZ) 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
- Af- Tropical wet climate [Done in previous post];
- Am – Tropical monsoon climate [This post];
- Aw- Tropical wet and dry climate [Next Post].
Tropical Monsoon Climate
- Monsoons are land and sea breezes on a much larger scale.
- Unlike equatorial wet climate, monsoon climate is characterized by distinct wet and dry seasons associated with seasonal reversal of winds.
- Floods in wet season and droughts in dry season are common.
- Usually there are three seasons namely summer, winter and rainy season.
Distribution of Tropical Monsoon Climate
- Occur within 5° to 30° N and S of the equator.
- On-shore [sea to land] tropical monsoons occur in the summer and off-shore [land to sea] dry monsoons in the winter.
- They are best developed in the Indian sub-continent, Burma, Thailand, Laos, Cambodia, parts of Vietnam and south China and northern Australia.
- The basic cause of monsoon climates is the difference in the rate of heating and cooling of land and sea (This is old theory. New theory will be explained while studying Indian Climate).
- In the summer, when the sun is overhead at the Tropic of Cancer, a low pressure is created in Central Asia.
- The seas, which warm up much slower, remain comparatively at high pressure. At the same time, the southern hemisphere experiences winter, and a region of high pressure is set up in the continental interior of Australia.
- Winds blow outwards as the South-East Monsoon, to Java, and after crossing the equator are drawn towards the continental low pressure area reaching the Indian sub-continent as the South-West Monsoon (Coriolis force).
- In the winter, conditions are reversed.
- Monthly mean temperatures above 18 °C.
- Temperatures range from 30-45° C in summer. Mean summer temperature is about 30°C.
- In winters, temperature range is 15-30° C with mean temperature around 20-25° C.
- Annual mean rainfall ranges from 200-250 cm. In some regions it is around 350 cm.
- Places like Cherrapunji & Mawsynram receive an annual rainfall of about 1000 cm. [They lie on the windward side of the Meghalaya hills, so the resulting orographic lift (orographic rainfall) enhances precipitation. Also, they are located between mountains which enhances cloud concentration due to funneling effect]
- Seasons are chief characteristics of monsoon climate.
The cool, dry season (October to February)
- Out blowing dry winds, the North-East Monsoon, bring little or no rain to the Indian sub-continent.
- However, a small amount of rain falls in Punjab from cyclonic sources (Western Disturbances: Frontal precipitation brought by jet streams) and this is vital for the survival of winter cereals.
- North-East Monsoons blowing over the Bay of Bengal acquires moisture and bring rains to the south-eastern tip of the peninsula at this time of the year (Nov-Dec).
The hot dry season (March to mid-June)
- The temperature rises sharply with the sun’s northward shift to the Tropic of Cancer.
- Day temperatures of 35° C are usual in central India and the mean temperature in Sind and south India may be as high as 44° C.
- Coastal districts are a little relieved by sea breezes. There is practically little rain. [Hailstorms (thunderstorms with hail) occurs here and there]
The rainy season (mid-June to September)
- With the ‘burst’ of the South-West Monsoon in mid-June, torrential downpours sweep across the country. Almost all the rain for the year falls within this rainy season.
- This pattern of concentrated heavy rainfall in summer is a characteristic feature of the Tropical Monsoon Climate.
The Retreating Monsoon
- The amount and frequency of rain decreases towards the end of the rainy season. It retreats gradually southwards after mid-September until it leaves the continent altogether.
- The skies are clear again and the cool, dry season returns in October, with the out blowing North-East Monsoon.
The role of monsoons in India is vital for its economy.
Tropical Marine Climate
- Outside the monsoon zone, the climate is modified by the influence of the on-shore Trade Winds all the year round. This type of climate is called Tropical Marine Climate. Such a climate has a more evenly distributed rainfall.
- Such a climate is experienced in Central America, West Indies, north-eastern Australia, the Philippines, parts of East Africa, Madagascar, the Guinea Coast and eastern Brazil.
- The rainfall is both orographic where the moist trades meet upland masses as in eastern Brazil, and convectional due to intense heating during the day and in summer.
- Its tendency is towards a summer maximum without any distinct dry period.
- Due to the steady influence of the trades, the Tropical Marine Climate is more Favourable for habitation, but it is prone to severe tropical cyclones, hurricanes or typhoons.
Tropical Monsoon Forests
Drought-deciduous forest; dry forest; dry-deciduous forest; tropical deciduous forest.
- Broad-leaved hardwood trees. Well developed in southeast Asia.
- Trees are normally deciduous, because of the marked dry period, during which they shed their leaves to withstand the drought [They shed their leaves to prevent loss water through transpiration].
- The forests are more open and less luxuriant than the equatorial jungle and there are far fewer species.
- Where the rainfall is heavy, e.g. in southern Burma, peninsular India, northern Australia and coastal regions with a tropical marine climate, the resultant vegetation is luxuriant.
- With a decrease in rainfall in summer, the forests thin out into thorny scrubland or savanna with scattered trees and tall grass.
- In parts of the Indian sub-continent, rainfall is so deficient that semi-desert conditions are found in summer. Monsoonal vegetation is thus most varied, ranging from forests to thickets, and from savanna to scrubland.
Population and Economy in Monsoon Climate
- Monsoon climatic regions support high population density.
- Income levels are low as most of these regions are underdeveloped or developing.
- Subsistence farming is the main occupation. (crops grown with an intention to secure food for the season. The crops are not sold as the production is very low).
- Intensive cultivation is common in regions with irrigational facilities.
- Shifting cultivation is followed in North-East India and South-East countries.
- Major crops include rice, sugar, cotton, jute, spices, etc..
- Cattle and sheep rearing is carried out for domestic and commercial purposes. Livestock industry is not as profitable as in temperate regions.
Agricultural Development in the Monsoon Lands
- Much of the monsoon forest has been cleared for agriculture to support the very dense population. Subsistence agriculture is the major occupation.
- Farms are small and the people are forever ‘land hungry.’ Industrialization make things worse.
- Tropical agriculture dependent on natural rainfall and a large labour force, reaches its greatest magnitude in the monsoon lands.
- Farming is the dominant occupation of the Indian sub-continent, China, South- East Asia, eastern Brazil and the West Indies. The following types of agriculture are recognizable.
- Rice is the most important staple crop.
- Irrigation water from rivers, canals, dams or wells is extensively used in the major rice producing countries.
- Other food crops like maize, millet, sorghum, wheat, gram and beans are of subsidiary importance. They are cultivated in the drier or cooler areas where rice cannot be grown.
Lowland cash crops
- The most important crop in this category is cane sugar.
- As much as two-thirds of world’s sugar production comes from tropical countries.
- Some of the major producers include India, Java, Formosa, Cuba, Jamaica, Trinidad and Barbados.
- Jute is confined almost entirely to the Ganges – Brahmaputra delta, in India and Bangladesh.
- Other crops include cotton, a major commercial crop of the Indian sub-continent.
Highland plantation crops
- The colonization of tropical lands by Europeans gave rise to a new form of cultivated landscape in the cooler monsoonal highlands.
- Thousands of acres of tropical upland forests were cleared to make way for plantation agriculture in which tea and coffee are the most important crops.
- Coffee originated in Ethiopia and Arabia.
- But Brazil accounts for almost half the world’s production of coffee.
- It is mainly grown on the eastern slopes of the Brazilian plateau.
- The crop is also cultivated on the highland slopes in the Central American states, India and eastern Java.
- Tea originated in China and is still an important crop there.
- It requires moderate temperatures (about 15° C), heavy rainfall (over 150 cm) and well drained highland slopes.
- It thrives well in the tropical monsoon zone (highlands).
- The best regions are thus the Himalayan foothills of India and Bangladesh, the central highlands of Sri Lanka and western Java, from all of which it is exported.
- In China tea is grown mostly for local consumption.
- Most of the forests yield valuable timber, and are prized for their durable hardwood.
- Lumbering is undertaken in the more accessible areas. This is particularly important in continental South-East Asia.
- Of the tropical deciduous trees, teak, of which Burma is the leading producer, is perhaps the most sought after. It is valuable on account of its great durability, strength, immunity to shrinkage, fungus attack and insects.
- Teak logs are so heavy that they will not float readily on water. It is therefore necessary to ‘poison’ the tree several years before actual felling, so that it is dry and light enough to be floated down the Chindwin and the Irrawaddy to reach the saw mills at Rangoon.
- Other kinds of timber include Neem, Banyan, Mango, Teak, Sal, Acacia, Eucalyptus
- Together with the forests are bamboo thickets, which often grow to great heights.
- Burma alone accounts for as much as three – quarters of the world’s production.
- It is such a durable timber that it is extensively used for ship building, furniture and other constructional purposes.
- This most primitive form of farming is widely practiced.
- Instead of rotating the crops in the same field to preserve fertility, the tribesmen move to a new clearing when their first field is exhausted.
- Maize, dry padi, sweet potatoes and some beans are the most common crops.
- Farming is entirely for subsistence, i.e. everything is consumed by the farmer’s family, it is not traded or sold.
- As tropical soils are rapidly leached and easily exhausted, the first crop may be bountiful but the subsequent harvests deteriorate.
- Shifting cultivation is so widely practiced amongst indigenous peoples that different local names are used in different countries.
Name of Shifting Cultivation
|Africa and Central America||Milpa|
Can be a [tough] prelims question under social geography.
Explain the following statements.
- The east coasts of continents within the tropics have much heavier rainfall than the interiors or the west coasts [Hint: Easterly trade winds].
- Near the equatorial latitudes, the period of maximum rainfall is closely related to the movements of the overhead sun [Hint: Inter-Tropical Convergence Zone shifts according to the apparent movement of the Sun].
- There is a marked difference in temperature between the east and west coasts of countries in latitudes 20° to 35°N [Hint: Ocean currents].
The seasonal reversal of winds is the typical characteristic of
- Equatorial climate
- Mediterranean climate
- Monsoon climate
- All of the above climates