Positive IOD may re-emerge this year, likely to boost south-west monsoon

Positive Indian Ocean Dipole (IOD) or Indian Nino, a climate pattern that results in irregular oscillations of sea surface temperatures in the Indian Ocean, may re-emerge for the second consecutive year in the latter half of 2024, two Australian weather agencies have said.

A positive IOD can boost the performance of India’s southwest monsoon, depending on when it develops. For example, in 2019, a strong IOD event that developed during the late monsoon season compensated for a 30 per cent rainfall deficit in June, experts said.

Australian national weather agency Bureau of Meteorology (BoM) said, “Along with atmospheric indicators, the model outlooks indicate a positive IOD event may be developing. If a positive IOD develops, it would be earlier than usual.”  

BoM said the Indian Ocean Dipole (IOD) index for the week ending April 28, 2024, was +0.68 °C, above the positive IOD threshold (+0.40 °C). “This is its seventh week above the positive IOD threshold. Typically, a positive IOD event is considered underway once the IOD index is sustained above +0.40 °C for about 8 weeks,” it said.

Australia’s private weather forecaster Weatherzone said it is likely that a positive IOD event will be declared.   

1st time since 1960

It is for the first time since 1960 that the event is recurring for a second consecutive year since record-keeping began. Despite IOD, the Indian monsoon was rain-deficient last year. 

This was due to the emergence of El Nino, which results in prolonged dry periods and drought in Asia — particularly India — in June 2023. The IOD is less powerful than El Niño and hence during such an event, the former’s impact is limited. 

It affected the agriculture sector with foodgrains production in the 2023-24 crop year to June estimated 6 per cent lower at 309.34 million tonnes compared with 2022-23. 

With La Nina predicted to emerge during June-August this year, the development IOD will likely boost the Indian agriculture sector. Also, it is likely to recharge reservoirs and other water sources, where the storage level is precarious.

A monsoon with adequate rains followed by good harvest will likely boost India’s rural sector. 

May could make or break

Weatherzone said if the IOD index is above +0.4°C for at least 3 consecutive months, it is a sign that a positive IOD is underway. Pointers are that the second consecutive positive IOD is developing in the next few months. However, May is shaping up to be a time to make-or-break this event, it said.

The Bureau of Meteorology said all five international climate models surveyed by it suggest positive IOD conditions in May. “However, at this time of year the confidence in model IOD forecasts beyond autumn is low.” it said.

Experts said a positive IOD can help rainfall in the Indian subcontinent and along the African coastline, while reducing rainfall in Australia, south-east Asia, and Indonesia.  

The India Meteorological Department (IMD) has predicted a higher-than-normal rainfall during the south-west monsoon, while  private forecaster Skymet said it would be normal this year. 

Weatherzone said if a tropical cyclone develops in the Bay of Bengal during April or May, there is a very high likelihood that a positive IOD event will occur that year. 

La Nina emergence

If the tropical activity is significant near India or Australia, the positive IOD event will become far more likely to occur, it said.

For India, the early emergence of IOD could help get higher rainfall during the south-west monsoon, particularly when it is feared that its setting could be affected by the dissipating El Nino.

While the Bureau of Meteorology has said El Nino is over, the Climate Prediction Center (CPC), an arm of the US National Oceanic and Atmospheric Administration, has said there is a 85 per cent chance of a transition to El Nino Southern Oscillation neutral by June 2024.

Apart from IOD, the other development that should cheer India is the  likelihood of La Nina, which brings more rains to India, emerging during June-August 2024. 

The emergence of El Nino last year severely affected India with water in 90 per cent of its 150 major storages dropping below 50 per cent of capacity. In particular, southern India is facing a precarious situation with groundwater levels, too, declining.