Geographical factors influencing the climate of Assam – APSC

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Assam falls within the sub-tropical monsoon regime. The special climatic characteristics of Assam are heavy downpours with high temperatures during summer and low rainfall associated with low temperatures.

Although it is part of the south-east Asiatic monsoon lands, its peculiar location and topography have given it its own type of climate. According to Vladimir Koppen, Assam enjoys a humid Mesothermal Gangetic type of climate.

The climate of Assam varies from part to part within the state depending on the location, physiography and other physical factors.

Factors Influencing the Climate of Assam

  • The physiography of Assam and relief of the adjacent region.
  • The alternating pressure condition over north-west India and the Bay of Bengal.
  • The predominance of moist tropical maritime air mass (south-west monsoon) that blows over the state.
  • The periodic visit of the Mediterranean cyclonic disturbances (Western disturbances) during the later winter season.
  • Local mountain and valley winds.
  • Presence of numerous extensive water bodies, vast forest and local cyclonic development, etc.
  • The mountain and plateau on the north, east and south and the opening on the west also play a significant role in shaping the character of the climate of the state.

Characteristics of the Climate of Assam

  • The cold valley winds begin to blow from valleys to the hills from about 10 a.m. to about 10 p.m. and from mountains to the valleys from about 10 p.m. to about 9 a.m.
  • The mountain winds make the weather of the valleys mild during the summer season but during the winter season, this wind makes their weather cooler.
  • In the pre-monsoon period especially in March, the weather becomes hazy with dust in the sky, as a result, humidity in the air decreases but the temperature increases and the visibility decreases.
  • The weather of Assam as well as the entire northeast remains cloudy for days in April and May due to the influence of tropical cyclones that occur frequently along the coastal regions of the Bay of Bengal.
  • Hence, in general, the climate of Assam is characterised by relative coolness, high relative humidity, heavy rainfall in the summer season and drought in the winter season.

Temperature Condition of Assam

  • In different districts of the state the mean annual maximum temperature, i.e. July-August, ranges from 30 to 33°C and the minimum temperature, i.e. December-January, ranges from 8 to 15°C.
  • The two valleys of the state experience the highest temperature in July (in the period of south-west monsoon) and experience the lowest temperature during January.
  • The highest temperature recorded in three different places, i.e. Dibrugarh in the easternmost part, Tezpur in the central part and Dhubri from the westernmost part of the Brahmaputra valley are 37°C, 36°C and 37°C, respectively.
  • The lowest temperatures recorded in these three places are 6°C, 7°C and 8°C, respectively.

Rainfall Condition of Assam

  • Assam experiences an average annual rainfall of 230 cm.
  • The average annual rainfall is 6 cm during the winter (December to February) and in summer (March to May) it is about 64 cm.
  • The maximum rainfall is 146 cm and it is experienced from June to September, i.e. in the monsoon period.
  • The rainless months in the state generally are December, January and February.

Assam may be divided into three distinct rainfall belts on the basis of the nature of the distribution of rainfall. These regions are as follows:

  • Heavy rainfall belt: Lakhimpur, Dhemaji, Dibrugarh, Tinsukia, Sibsagar, Jorhat, Dhubri, Kokrajhar, Bongaigaon, Chirang, Goalpara, Cachar and Karimganj.
  • Medium rainfall belt: Barpeta, Nalbari, Baksa, Kamrup, Darrang, Udalguri, Sonitpur, Morigaon, Nagaon, Golaghat and Karbi Anglong.
  • Low rainfall belt:
    • It includes the southern part of the Nagaon district. It forms a distinct rain shadow area north of the Meghalaya Plateau.
    • The belt runs from Guwahati eastward along the Meghalaya foothills through Hojai, Lanka and Lumding.
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