The country is likely to receive a normal monsoon for the fourth consecutive year, the India Meteorological Department (IMD) said in its first Long Range Forecast (LRF) for this year.


What is ‘monsoon’?

Out of a total of 4 seasonal divisions of India, monsoon occupy 2 divisions, namely.

  • The southwest monsoon season – Rainfall received from the southwest monsoons is seasonal in character, which occurs between June and September.
  • The retreating monsoon season – The months of October and November are known for retreating monsoons.


What is ‘Long Period Average’?

  • The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
  • According to the IMD, the “LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30 years, 50 years, etc”.
  • The IMD’s current prediction of a normal monsoon was based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average. The IMD has in the past calculated the LPA at 88 cm for the 1961-2010 period, and at 89 cm for the period 1951-2000.


Monsoon prediction by IMD –

  • IMD brands the monsoon as ‘normal’ or ‘deficient’ based on how it fares against its benchmark Long Period Average (LPA).
  • LPA is the average rainfall received by the country as a whole during the south-west monsoon, for a 50-year period.
  • Deficient rainfall – The country is said to have received deficient rainfall if the actual rainfall falls below 90 per cent of LPA.
  • Excess rainfall – The country is said to have received excess rainfall if the rainfall is greater than 110 per cent of LPA.
  • Normal rainfall – It is deemed ‘normal’ when the actual rainfall received falls between 96 and 104 per cent of LPA. The IMD has recently changed the definition of a “normal” monsoon by reducing average rainfall received during rainy season from 89 cms to 88 cms.


About Indian Meteorological Department – 

  • IMD was established in 1875.
  • It is an agency of the Ministry of Earth Sciences of the Government of India.
  • It is the principal agency responsible for meteorological observations, weather forecasting and seismology.