• India will experience above-normal monsoon rains this season on the back of favourable La Nina conditions, the IMD said on April 15.

• The seasonal rainfall will be on the higher side of ‘above-normal’, and pegged it at 106 per cent of the Long Period Average (LPA) with a model error of 5 per cent. 

• 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. It acts as a benchmark while forecasting the quantitative rainfall for that region for a specific month or season.

• The LPA of the seasonal rainfall over the country as a whole based on data of 1971-2020 is 87 cm.

There are 5 categories of monsoon rainfall: 

i) Deficient (less than 90% of LPA)

ii) Below normal (90 to 95% of LPA)

iii) Normal (96 to 104% of LPA)

iv) Above normal (105 to 110% of LPA)

v) Excess (more than 110% of LPA).

• Parts of the country are already battling extreme heat and a significantly high number of heat wave days are expected in the April to June period. This could strain power grids, and result in water shortages in several areas.  

• A prediction of above-normal rainfall during the monsoon season, therefore, comes as a huge relief to the nation.

• El Nino conditions are prevailing at present. ENSO neutral conditions are expected in the first half of the monsoon season. Thereafter, models suggest, La Lina conditions may set in by August-September.

• Positive Indian Ocean Dipole conditions, favorable for the Indian monsoon, are predicted during the season.

• The Indian Ocean Dipole (IOD), also known as Indian Nino, is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia. A positive IOD is considered good for the Indian monsoon. 

What is El Nino and La Nina?

• El Nino and La Nina events are a natural part of the global climate system. They occur when the Pacific Ocean and the atmosphere above it change from their neutral (‘normal’) state for several seasons.

• El Nino, which is the warming of the waters in the Pacific Ocean near South America, is generally associated with the weakening of monsoon winds and dry weather in India.    

• La Nina, which is the opposite of El Nino, typically brings good rainfall during the monsoon season.

• These changes in the Pacific Ocean and its overlying atmosphere occur in a cycle known as the El Nino–Southern Oscillation (ENSO). 

• The term ‘El Nino’ translates from Spanish as ‘the boy-child’. Peruvian fishermen originally used the term to describe the appearance, around Christmas, of a warm ocean current off the South American coast. It is now the commonly accepted term to describe the warming of the central and eastern tropical Pacific Ocean. ‘La Nina’ translates as ‘girl-child’ and is the opposite ENSO phase to El Nino.

How does the IMD forecast monsoon?

• The India Meteorological Department (IMD) issues operational forecast for the southwest monsoon season (June to September) rainfall for the country as a whole in two stages. 

• The first stage forecast is issued in April and the second stage forecast is issued in May/June.

• Since 2021 IMD has implemented a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall over the country by modifying the existing two stage forecasting strategy. 

• The new strategy uses both dynamical and statistical forecasting system. Multi-Model Ensemble (MME) forecasting system based on coupled global climate models (CGCMs) from different global climate prediction centres, including IMD’s Monsoon Mission Climate Forecast System (MMCFS) is used in dynamical forecast system. 

• As per the new LRF strategy, the first stage forecast issued in middle of April consist of quantitative and probabilistic forecasts for the country as a whole and the spatial distribution of probabilistic forecasts for the tercile categories (above normal, normal, and below normal) of the seasonal rainfall (June-September) over the country.

• The second stage forecast issued around end of May consists of an update for the seasonal rainfall forecast issued in April along with the probabilistic forecasts for the seasonal rainfall over the four homogenous regions of India (northwest India, central India, south Peninsula and northeast India) and monsoon core zone (MCZ). 

• In addition, quantitative and probabilistic forecasts for the country as a whole and the spatial distribution of probabilistic forecasts of rainfall (above normal, normal, and below normal) over the country during June are also issued during the second stage forecast.

• In continuation to the above forecasts, a monthly rainfall forecast is issued around the end of June, July and August respectively for the subsequent one month.

• In addition, quantitative and probabilistic forecasts for the country as a whole, and the spatial distribution of probabilistic forecasts of rainfall for the second half (August-September) of the season are issued around the end of July along with the forecast for August.

• Data from the 1951-2023 period shows India experienced above-normal rainfall in the monsoon season on all the nine occasions when La Nina followed an El Nino event.

• The country gauged above-normal or normal monsoon in 20 out of the 22 La Nina years.

Importance of normal monsoon in India

• Monsoon brings relief to dry and parched land in the form of rain, and affects Indian agriculture in a very substantial measure. The impact of the  monsoon on Indian economy is more pronounced. 

• Normal rain is critical for India’s agricultural landscape, with 52 percent of the net cultivated area relying on it. It is also crucial for the replenishing of reservoirs critical for drinking water apart from power generation across the country.

• Rainfed agriculture accounts for about 40 percent of the country’s total food production, making it a crucial contributor to India’s food security and economic stability. 

• Excessive rain leads to floods in certain areas, while little or no rain in other parts bringing drought and famine resulting in acute distress to millions.

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