Southwest monsoon likely to be normal across India, says IMD

The long period average rainfall for the season over the entire country between 1971-2020 stands at 87 cm

India is likely to witness a normal south west monsoon for the fourth consecutive year, with the India Meteorological Department (IMD) forecasting that the country would receive 99 per cent of its average rainfall between June and September.

The met office, however, downgraded the mean monsoon precipitation as India’s long period average rainfall for the monsoon season now stands at 87 cm (1971-2020) as against 88 cm (1961-2010) which was considered till last year. The dip, the weathermen say, is due to natural climatic variabilities.

"Southwest monsoon seasonal (June to September) rainfall over the country as a whole is most likely to be normal (96-104 per cent of Long Period Average). Quantitatively, the monsoon seasonal (June to September) rainfall is likely to be 99 per cent of the LPA with a model error of plus or minus 5%,” IMD director general M Mohapatra said at a press conference here.

The south west monsoon is crucial for India's $2.7 trillion economy, as it brings nearly 75 per cent of the rain needed by farms, besides replenishing reservoirs and aquifers.

Nearly half of India's farmland gets no irrigation and is dependent on the annual rains from June to September. Farming accounts for nearly 15 per cent of the economy but sustains more than half of a population of 1.3 billion.

A favourable global weather condition – continuation of the La Nina (cooling of central and east Pacific ocean) till at least the middle of the monsoon season and neutrality of Indian Ocean Dipole (a temperature seesaw between the Arabian Ocean and Bay of Bengal) in the initial months bolsters the possibility of a normal monsoon.

While La Nina conditions are generally associated with surplus monsoon, the second half of the monsoon season may experience a negative IOD, which has an adverse effect.

As sea surface temperatures over the Pacific and the Indian Oceans strongly influence the Indian monsoon, IMD monitors the evolution of sea surface conditions over these oceans.

On the dip in average rainfall value, the weather bureau said it was part of natural multi-decadal epochal variability of dry and wet epochs of all India rainfall. Such a change was last introduced in 2018 when the average was brought down to 88 cm from the previous mean of 89 cm.

"Presently the south west monsoon is passing through a dry epoch, which started in the decade of 1971-80. The 2021-2030 will be a near normal epoch and southwest monsoon will enter into a wet epoch from the decade of 2031-40,” said Mahapatra.

The all-India annual average rainfall figure now stands at 116 cm (1971-2020) as against the previous average of 117.69 cm. The new normal has been computed using data from 4,132 rain gauges in 703 districts.

The weather agency will come out with the monsoon onset forecast around May 15 and the second stage forecast by May-end.

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