Central idea

India’s four-year run of abundant summer monsoon rainfall is likely to end this year, with the India Meteorological Department (IMD) forecasting a 4% shortfall in the coming season.
The monsoon forecast for 2022 is still categorized as “normal” but at 96% of the long-period average (LPA), it is at the lowest end of the range.
El Nino, a cyclical phenomenon of warming in the central Pacific, is believed to be the key factor responsible for the below-normal forecast.

Factors affecting the forecast

El Nino: It has been linked to diminished rainfall in six out of 10 years in India, and 2022 is expected to see its development.
La Nina: It has been influencing the rainfall in India since 2019 and is expected to end this year.
Reduced snow cover in Eurasia: It can have a positive impact on the monsoon forecast, and this year’s snow cover in Eurasia was below normal.
Positive phase of the Indian Ocean Dipole (IOD): IOD could result in more moisture and rainfall over India during August and September, and therefore, have a reduced impact of the El Nino.
IMD’s dynamical monsoon forecast techniques: It involves the simulation of global atmospheric and ocean conditions to forecast climate conditions, which the IMD has started to rely on more heavily in recent years.

El Nino and La Nina are two opposite phases of the El Nino-Southern Oscillation (ENSO) cycle.
ENSO is a naturally occurring phenomenon that involves the interaction between the ocean and atmosphere in the equatorial Pacific.

Here is a detailed comparison of El Nino and La Nina

	El Nino	La Nina
Definition	Warmer-than-normal sea surface temperatures	Cooler-than-normal sea surface temperatures
Frequency	Every two to seven years	Every two to seven years
Duration	Several months to a year or more	Several months to a year or more
Impact on winds	Weakens trade winds, leading to changes in patterns	Strengthens trade winds, leading to changes in patterns
Impact on rains	Reduces rainfall and can cause droughts	Increases rainfall and can cause flooding
Impact on temp.	Warmer-than-average temperatures	Colder-than-average temperatures
Global effects	Droughts in Asia and Africa, floods in Americas	Floods in Asia and Africa, droughts in South America

El Nino	La Nina
Associated with weak monsoons and drought-like conditions in India	Associated with above-normal rainfall and floods in India
Sea surface temperature in the equatorial Pacific Ocean rises above normal levels	Sea surface temperature in the equatorial Pacific Ocean drops below normal levels
Changes in the atmospheric circulation patterns	Changes in the atmospheric circulation patterns
Shift in the location of the jet stream, affecting the strength and direction of the monsoon winds	Increase in the strength of the monsoon winds, bringing more moisture and rainfall to India
Results in reduced rainfall, dry spells, and heatwaves, leading to crop failures and water scarcity	Excessive rainfall can also lead to floods and landslides, causing damage to crops and infrastructure

The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
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.
LPA refers to the average rainfall recorded from June to September for the entire country, the amount of rain that falls every year varies from region to region and from month to month.
The IMD’s prediction of a normal monsoon is based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average.
It has in the past calculated the LPA at 88 cm for the 1961-2010 period, and at 89 cm for the period 1951-2000.

Rainfall Distribution Categories	Percentage Departure of Actual Rainfall from LPA
Normal or Near Normal	+/- 10% of LPA (between 96-104% of LPA)
Below Normal	Less than 10% of LPA (90-96% of LPA)
Above Normal	104-110% of LPA
Deficient	Less than 90% of LPA
Excess	More than 110% of LPA