The Tropical Monsoon Climate
- Also known as a tropical wet climate or trade-wind littoral climate.
- Marked by seasonal reversal in wind direction giving well defined wet & dry seasons.
- Mainly due to the difference in specific heat capacity between land and sea.
- Tropical Monsoon climate is best developed in India, Myanmar, Thailand, Laos, Vietnam, Bangladesh, South China & Northern Australia.
- Basically found beyond the equatorial region between 10 degree and 25 degree and North and South of the equator.
- The tropical monsoon climate experiences abundant rainfall like that of the tropical rain forest climate, but it is concentrated in the high-sun season.
- Being located near the equator, the tropical monsoon climate experiences warm temperatures throughout the year.
- In the summer, when sun is overhead at Tropic of cancer, the great land masses of the northern hemisphere are heated.
- Central Asia, backed by the lofty Himalayan ranges, gets heated intensely, creating a region of extremely low pressure.
- The seas, which warm up much slower, remain comparatively cool.
- At the same time, the southern hemisphere experiences winter, & a region of high pressure is set up in the continental interior of Australia.
- Winds blow outward as south east monsoon to java, & after crossing the equator are drawn towards the continental low pressure area reaching the Indian subcontinent as south west monsoon.
- In winters, the conditions are reversed & the sun is overhead at the Tropic of Capricorn while the central Asia gets extremely cold, creating a region of high pressure with winds out-blowing as North East Monsoon.
- On crossing the equator, the winds are attracted to the low pressure centre in Australia & arrive in Northern Australia as the North West Monsoon.
- In other parts of the world, which experience a tropical monsoon climate, a similar reversal of wind directions occurs.
- The monsoon climate has a high mean annual temperature and a small annual temperature range like equatorial climate.
Seasons of Tropical Monsoon Climate
1. Cool, Dry Season (Oct - Feb)
- Average temperature ranges between 19 degree Celsius and 23 degree Celsius with frost may occur at night in colder north; a centre of high pressure is developed over Punjab.
- Out-blowing dry winds, the N-E Monsoon, bring little or no rain in northern Indian subcontinent;
- However a small amount of rain falls in Punjab from cyclonic sources, vital for survival of winter cereals.
- When the N-E Monsoon blows over the Bay of Bengal, it acquires moisture & thus brings rain to the south eastern tip of Indian peninsula at this time of the year
- For e.g. Chennai receives 125 Cm of rainfall during October & November, accounting for half its annual rainfall.
2. Hot Dry Season (March - Mid June)
- The temperature rises sharply with the sun’s northward shift to the Tropic of Cancer with average temperature of 35 degree Celsius.
- Practically, no rain anywhere with an intense low pressure generated over N-W India.
3. Rainy Season (Mid June - Sep)
- With the burst of S-W monsoon in mid-June, torrential downpours sweep across the country.
- Almost 95 % of annual rainfall is concentrated within this rainy season of approx. 4 months.
- This pattern of concentrated heavy rainfall in summer is a characteristic feature of the tropical monsoon climate.
4. The Retreating monsoon
- Amount & frequency of rain decreases towards the end of the rainy season;
- It retreats gradually southwards after mid-September until it leaves the continent altogether.
- Punjab plains which receive the S-W Monsoon earliest are the first to see the withdrawal of the monsoon.
- The skies are clear again & cool, dry season returns in October, with the N-E Monsoon.
Tropical Marine Climate
- This type of climate is experienced along the eastern coasts of tropical lands, receiving steady rainfall from trade winds all the time.
- These areas experience between 120 cm to 200 cm of rainfall annually & include -
(i) Central America
(ii) West Indies
(iii) N-E Australia
(v) Parts of East Africa
(vii) Guinea Coast
(viii) Eastern Brazil
- The rainfall is both orographic where moist trade winds meet upland masses as in eastern Brazil and convectional due to intense heating during the day in summers
- Tendency is towards a summer maximum as in monsoon lands, but without any distinct dry period.
- Regions which experience a tropical marine climate have hot & humid temperature all year round but annual temperature range is often quite small.
- Temperatures are higher during the wetter season and lower during the drier season.
- Due to the steady influence of the trades, the tropical marine climate is more favourable for habitation, but is more prone to severe tropical cyclones, hurricanes or typhoons.
Tropical Monsoon Forests
- The natural vegetation of tropical monsoon land depends on the amount of summer rainfall.
- Trees are normally Deciduous, because of the marked dry period, during which they shed their leaves to withstand drought.
- In tropical monsoon forests, the ecosystems which develop are very similar to the true rainforests which develop in equatorial climates, but are more open, less luxuriant & contains far fewer species.
- The layer structure of the forest trees consist of Canopy, understory & shrub layer with average height 25 - 45 m & average rainfall 100 - 200 cm.
- Most of the forests yield valuable timber & prized for their durable hardwood such as teak, Rosewood, Sal, sandalwood, Shisham, Banyan, Aracia & some varieties of Eucalyptus in N- Australia.
- Together with the forests are bamboo thickets, which often grow to great heights; thorny scrubs with scattered trees & long grass.
- Among hardwoods, Teak is extensively used for ship building, furniture & other construction purposes because of its high durability, strength, immunity to shrinkage, fungus & insects; with Burma alone accounting for 3/4th of the world production
Agricultural Development in Monsoon Lands
1. Major Food Crops
- Rice (Most important)
- Beans (in drier areas where rice cannot be grown)
2. Lowland Cash Crops
- Sugarcane - India, Java, Cuba, Jamaica, Formosa, Trinidad & Barbados
- Jute - Ganga Brahmaputra Delta in India & Bangladesh
- Manila hemp / Abaca - Philippines (used for making a high quality rope)
- Other crops include Indigo, Cotton, Banana, Coconut & Spices
3. Highland Plantation Crops
- Originated in Ethiopia & Arabia, where it is still grown
- But Brazil now accounts for half the world production
- Also grows on highland slopes of India, Eastern Java & Central American states
- Originated in China & still important crop there for local consumption.
- Major exporters are India, Java, Bangladesh & Srilanka.
- Also practised in Tropical monsoon forests entirely for subsistence (for consumption only)
- Major crops are sweet potato, beans, maize, paddy, yams & tapioca
- As tropical soils are mainly latosolic (high content of iron & aluminum oxide), hence rapidly leaches away & easily exhausted First crop may be bountiful, but the subsequent crops deteriorates.
- Shifting cultivation is so widely practised amongst indigenous peoples that different local names are used in different countries.
(i) Ladang - Malaysia
(ii) Taungya - Burma
(iii) Tamrai - Thailand
(iv) Caingin - Philippines
(v) Humah - Java
(vi) Chena - Sri Lanka
(vii) Milpa - Africa & Central America