Monsoon Climate And Forests

Monsoon climate, also known as the tropical monsoon climate, is found in the region bounded by the Tropic of Cancer and the Tropic of Capricorn. The region is influenced by the movement of inter-tropical convergence zone (ITCZ) and is hot and humid all around the year because the sun remains overhead.

Monsoon Climate And Forest

Monsoons are seasonal winds, blowing over the landmasses from the seas and vice-versa. They are characterized by a seasonal reversal in the wind direction, leading to variations in temperature and precipitation. Summer, winter, and rainy season are the three prominent and distinct seasons of this climatic region.

Monsoon Climate

Distribution

  • They are confined within 5 - 30 degrees latitudes on either side of the equator.
  • Indian subcontinent, Indo-China (Laos. Vietnam, Cambodia), Thailand. southern China and northern Australia are the regions experiencing this climate.

Winds

  • The seasonal reversal in the direction of winds is an outcome differential rate of heating and cooling of the continental landmasses and seawaters.
  • During the summers, a low-pressure region develops over Central Asia as the sun comes overhead the Tropic of Cancer. This causes the Asian landmass to heat up faster than the surrounding seas, which remain at a higher pressure in the northern hemisphere.
  • In the southern hemisphere, winter conditions prevail, leading to a high-pressure zone over northern Australia.
  • Winds blow outward from the Australian landmass towards Java (Indonesia) and are drawn towards the low-pressure region over the Indian subcontinent after crossing the equator, under the influence of the Coriolis force. These are the South-West monsoon winds.
  • During winters, a reversal in the wind direction occurs.

Temperature

  • Owing to the region's proximity to the tropics, it experiences warm to hot summers.
  • Average monthly temperature is above 18 degrees centigrade, but in summers the maximum can reach as high as 45 degrees centigrade.
  • The average temperature in the summer is around 30 degrees centigrade, with an overall temperature range of 30 to 45 degrees centigrade.
  • Winters are mild with a temperature range of 15 to 30 degrees centigrade. Mean temperature during winters is around 25 degrees centigrade.

Precipitation

  • The region experiences very high rainfall, which is concentrated in a few months.
  • Annual average rainfall is around 200-250 cm. However, some regions have a very high average of around 350 cm.
  • In India, Maysynram and Cherrapunji of Khasi Hills (Meghalaya) experience an annual rainfall of over 1000cm. They are located on the windward side of the hills, causing heavy orographic rainfall (caused by a lift of the monsoon winds). Due to the location in between mountains which causes a concentration of rain-bearing clouds, also known as the funnelling effect, these places receive very high rainfall.

Seasons

Unlike the equatorial climate which does not have distinct seasons, monsoon climate experiences striking differences in weather conditions based on the seasons.

The hot dry season

  • This lasts from March to mid - June.
  • The sun is in a northward shift to the Tropic of Cancer. This causes the temperatures to rise sharply.
  • Mean temperatures during the day cross 35 degrees centigrade in Central India. It can reach as high as 44 degrees centigrade in Sindh and also in south India.
  • In coastal areas, the temperatures are not so high, due to the influence of sea breezes.
  • Except for the occasional thunderstorms, there is little rainfall during this season.

The rainy season

  • This lasts from mid - June to September
  • The rains begin with the 'burst' of monsoon over the subcontinent. It results in torrential rainfall throughout the country.
  • Over 70 percent of the rainfall which the country receives in a year occurs in this season.
  • This can be termed a typical characteristic feature of monsoon type of climate i.e., concentrated heavy rainfall during the summer months.

The cold dry season

  • This season begins in October and lasts until February.
  • Also known as the season of retreating monsoon. As the sun begins its southward shift, south-west monsoon begins to retreat southwards until it leaves the Indian landmass completely.
  • The temperatures over the landmass begin to fall creating a high-pressure region over Indian subcontinent compared to the surrounding seas. This causes the winds to blow away from the landmass towards the sea.
  • The winds begin to blow from the northeast direction over the Bay of Bengal and cause some rainfall along the south-east coastal landmass of India in the months of November and December.
  • In the north, the Western Disturbances bring some amount of rain and snow, otherwise, the region remains dry. Frontal (cyclonic) rainfall due to the western disturbances is essential for the survival of winter crops.

Monsoon Forests

  • Also known as the Tropical Monsoon Forests.
  • These are mostly the trees of deciduous variety - they have a distinct season for the shedding of leaves. They shed their leaves during the dry/drought season to prevent transpiration losses.
  • They can be of two types - moist deciduous, where the rainfall exceeds 150cm, and dry deciduous where the average annual rainfall is less than 150cm.
  • They are made up of broad-leaf hardwood trees, similar to the equatorial rainforests. But the forests are not as dense, and they are more open with less diversity of species (flora as well as fauna).
  • Wherever the rainfall exceeds 200-250cm, evergreen rainforests of the equatorial type can be found. These are prominent in the southern Western Ghats, forests in the northeast, Andaman and Nicobar islands of India. They are also found in the islands of southeast Asia.
  • Wherever the rainfall is scanty, savanna type grasslands are found with scattered trees.
  • Hence, monsoon vegetation shows a great variation from dense forests to thorny scrublands (savanna).

Economy

  • These regions have a high population density.
  • Subsistence agriculture is the main type of crop cultivation, although shifting cultivation and plantation agriculture is also practised.
  • In the plains of north India, cereals like rice, wheat, maize etc. are cultivated apart from jute, sugarcane, and spices.
  • In the highlands of south and east India, plantation crops can be found - tea, coffee, rubber, banana etc
  • Lumbering is an important activity with the forest yielding durable hardwood. Teak is an important deciduous timber variety found in central India as well as in Myanmar. Other timber varieties include Sal, Acacia, Eucalyptus, Neem, Mango etc. Bamboo is also an important source of timber

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