IMD: Monsoon to be normal in India in 2021

The Indian Meteorological Department recently announced that the southwest monsoon is expected to be normal at 98% of the Long Period Average. This is mainly because the La Nina or El Nino weather conditions that affect monsoon rains in India are likely to be absent. Also, Indian Ocean Dipole that has direct bearing on Indian monsoon is also expected to be neutral this year.

Long Period Average

  • The Long Period Average of monsoon is 88 centimetres. The rainfall between 96% and 104% of LPA is considered as normal rainfall.
  • In 2020, rainfall in India was 109% of Long Period Average.
  • In 2019, the rainfall in India was 110% of Long Period Average.

Indian Ocean Dipole

The Indian Ocean Dipole is an irregular sea surface temperature fluctuation in Indian Ocean. During Indian Ocean Dipole, the western Indian Ocean becomes alternately colder and warmer than the eastern part of the ocean.

How are Monsoons predicted in India?

  • The IMD uses three approaches to predict monsoons in India. They are statistical method, dynamical method and the dynamical cum statistical method.
    Under statistical method, the predictors are identified. They are then related to historical occurrence of Monsoon in the past.
  • Under the dynamic method, the atmospheric and oceanic conditions are simulated.
  • The dynamic cum statistical method is empirical in nature. That is, it is verifiable and is based on observation or experience rather than theory. The empirical methods are used in countries such as US, UK, South Africa, Australia, Brazil.

When are Long Range Forecasts issued by IMD?

IMD issues Long Range Forecasts for rains in two stages. They are

  • The first stage is issued in mid-April. It consists of quantitative forecast of the season. That is between June and September.
  • The second stage forecast is issued by the end of June. This gives detailed forecasts about the rains.

Apart from this, the IMD also prepares forecasts for winter precipitation (January to March) and also a forecast for the north east monsoon (October to December).

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