India 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 released on April 14.
- India would get 99% of the rainfall of the long period average (LPA).
- The IMD’s prediction of a normal monsoon on April 14 was based on the long period average (LPA) of the 1971-2020 period, which is 87 cm. LPA was changed from 89 cm to 88 cm in 2018.
- A monsoon is considered “normal” when rainfall falls between 96% and 104% of the LPA.
About LPA
- The definition of the long period average (LPA) was meant to be updated every decade.
- The 89-cm average was computed based on a 50-year average from 1951 to 2000; the 88 cm based on average for the period from 1961 to 2010; and the latest is based on the average for the period from 1971 to 2020.
- An LPA is needed to smooth out regional, weekly, monthly and yearly rainfall variations trends so that a reasonably accurate prediction can be made.
- A 50-year LPA covers for large variations in either direction caused by freak years of unusually high or low rainfall as a result of events such as El Nino or La Nina.
Rainfall distribution categories
The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
- Excess: actual rainfall more than 110% of LPA.
- Above normal: Actual rainfall is 104-110% of LPA
- Normal: Actual rainfall is between 96-104% of LPA
- Below normal: Actual rainfall is is 90-96% of LPA;
- Deficient: Actual rainfall is less than 90% of LPA.
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