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Context
Indian Meteorological Department (IMD) predicted “near normal” southwest monsoon rainfall this year.
More in news
- The south-west monsoon, which makes its onset over India around May-end, contributes more than 70% of India’s annual showers.
- The forecast of a below average or near normal monsoon in 2019 is based primarily on prospective El Nino that is often associated with less rainfall.
- The IMD said monsoon rainfall (June-September) is likely to be 96% of the Long Period Average (LPA)
- The IMD also said the possibility of rainfall being excessive or ‘above normal’ was very low. The forecast of 96% is at the lower end of the band in which rainfall is classified as ‘normal’.
- Last year, rainfall was both below average as well as less than forecast. India as a whole received 91% of the LPA last year while IMD had forecast that it would get 97% rains. The distribution of rainfall was also erratic, with some parts of the country experiencing extreme rainfall and flash floods.
Long Period Average (LPA)
• LPA is the average rainfall recorded from June to September, calculated during the 50-year period.
• It is the benchmark while forecasting the quantitative rainfall for the monsoon season every year.
• IMD maintains an independent LPA for every homogeneous region of the country, which ranges from 71.6 cm to 143.83 cm.
• The region-wise LPA figures are: 143.83 cm for East and Northeast India, 97.55 cm for Central India, 71.61 cm for South Peninsular India, and 61.50 for Northwest India
• India receives an average of 89 cm of rainfall during the entire season — this is referred to as normal rainfall.
Rainfall distribution categories
IMD maintains five rainfall distribution categories on an all-India scale. These are:
• Normal or Near Normal: When per cent departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA
• Below normal: When departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA
• Above normal: When actual rainfall is 104-110% of LPA
• Deficient: When departure of actual rainfall is less than 90% of LPA
• Excess: When departure of actual rainfall is more than 110% of LPA
• LPA is the average rainfall recorded from June to September, calculated during the 50-year period.
• It is the benchmark while forecasting the quantitative rainfall for the monsoon season every year.
• IMD maintains an independent LPA for every homogeneous region of the country, which ranges from 71.6 cm to 143.83 cm.
• The region-wise LPA figures are: 143.83 cm for East and Northeast India, 97.55 cm for Central India, 71.61 cm for South Peninsular India, and 61.50 for Northwest India
• India receives an average of 89 cm of rainfall during the entire season — this is referred to as normal rainfall.
Rainfall distribution categories
IMD maintains five rainfall distribution categories on an all-India scale. These are:
• Normal or Near Normal: When per cent departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA
• Below normal: When departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA
• Above normal: When actual rainfall is 104-110% of LPA
• Deficient: When departure of actual rainfall is less than 90% of LPA
• Excess: When departure of actual rainfall is more than 110% of LPA
Different from global forecasts
- The IMD’s forecast deviates from that of private forecasting company, Skymet Weather, who predicted a “below normal” monsoon i.e. about 93% of the Long Period Average.
- According to the latest global forecasts, weak El Nino conditions have developed over equatorial Pacific Ocean and they are likely to persist this summer.
- However, IMD predict that El Nino would be weaken during monsoon month. There could be some impact on the monsoon from El Nino in the earlier weeks of June.
What is El Nino
- El Nino, means ‘little boy’ in Spanish. It is a weather system which re-emerges after a gap of about two to five years in the Pacific Ocean and its effects last for about 12 months on an average.
- El Nino leads to warming of sea surface temperatures, which in turn affects wind patterns and triggers both floods and droughts in different parts of the world
- A strong El Nino can cause severe drought in Australia, Southeast Asia and India, while drenching other parts of the world such as the U.S. Midwest and Brazil in rains.
- The opposite of El Nino is La Nina when sea surface temperatures in the central Pacific drop to lower-than-normal levels.
El Nino on Indian monsoon
- Scientists and researchers maintained that there is no direct correlation between the El Nino events and the monsoon has been established yet.
- The El Nino events in 1965, 1972, 1982 and 1987 were bad for India but the 1997 El Nino, despite being the strongest in the century, did not affect monsoons. This led many experts to conclude that the link between monsoons and global weather event was wearing off. But the India Meteorological Department still takes into account El Nino for forecasts.
Other factors on Indian monsoon
• Location of warming in the pacific: Researchers believe that the location of the warming in the Pacific may possibly have an influence on the monsoon. Anomalous warming in the Central and East could have a more profound adverse impact on the monsoon than when the warming shifts to the adjoining far east Pacific. Current conditions suggest that the warming is in the Central and East region than the far east Pacific, which could suggest a weaker monsoon this year.
• Extent of the Himalayan/Eurasian snow cover: Less snow cover means a warmer subcontinent, which can help to intensify the monsoon circulation and bring more rain.
• Progressive heating of the land during April-May-June
• Location of warming in the pacific: Researchers believe that the location of the warming in the Pacific may possibly have an influence on the monsoon. Anomalous warming in the Central and East could have a more profound adverse impact on the monsoon than when the warming shifts to the adjoining far east Pacific. Current conditions suggest that the warming is in the Central and East region than the far east Pacific, which could suggest a weaker monsoon this year.
• Extent of the Himalayan/Eurasian snow cover: Less snow cover means a warmer subcontinent, which can help to intensify the monsoon circulation and bring more rain.
• Progressive heating of the land during April-May-June
Way Ahead
The rain-fed kharif crops are heavily dependent on the monsoon and the quantity of rainfall determines agricultural production. IMD will monitor the El Niño conditions and update its forecast in the first week of June, with predictions for region-wise and month-wise rainfall. The monsoon forecast is crucial, as it directly influences agricultural production and has a spiralling impact on inflation and growth.
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