MONSOON

Shifting Tides: Could Approaching La Niña Bring Above-Normal Rains to India in the Latter Half of Monsoon?

Dark clouds dump rain over Vijayawada, Andhra Pradesh. (Mahesh G/BCCL Vijayawada) — Dark clouds dump rain over Vijayawada, Andhra Pradesh.
(Mahesh G/BCCL Vijayawada)

The National Oceanic Atmospheric Administration (NOAA) has announced the conclusion of the El Nino phase, which has significantly influenced global weather patterns over the past year. This transition sets the stage for a potential shift to La Niña in the coming months, with implications for weather conditions worldwide, including the Indian monsoon.

Michelle L'Heureux, who heads NOAA's ENSO team, has highlighted a 65% likelihood of La Niña emerging between July and September. Unlike El Niño, which warms the central and eastern Pacific, La Niña is characterised by cooler sea surface temperatures in these regions.

The cycle between El Niño, La Niña, and neutral phases recurs every two to seven years, impacting global weather events such as wildfires, tropical cyclones, floods, and prolonged droughts.

Impact on India

NOAA's forecast of a 65% chance of La Niña from July to September suggests favourable conditions for robust monsoon rainfall in the latter part of the season for India. This projection aligns with the India Meteorological Department's (IMD) prediction of above-normal monsoon rainfall, offering hope amidst the current phase of weakened monsoon activity across the country.

"The developing temperature anomalies indicate a positive sign for the monsoon, even if La Niña is officially declared around August," M. Rajeevan, a veteran meteorologist and former secretary of the Union Ministry of Earth Sciences, commented on the latest US forecast. "The transition from neutral to La Niña during the monsoon season bodes well," he emphasised.

Factors affecting indication

Niño indices: Key indicators such as the Niño indices, particularly Niño 4 and Niño 1+2, have shown slight warming, though insufficient to trigger the onset of La Niña. The Niño 3.4 index remains neutral, suggesting a lack of significant cooling necessary for La Niña development.

The Indian Ocean Dipole (IOD): IOD currently remains in a neutral state. Known for its significant influence on the Indian Summer Monsoon (ISM), the IOD requires a threshold crossing of +0.4°C to positively impact monsoon rainfall. Its neutral status, combined with the transitional phase towards La Niña, introduces uncertainties for the upcoming monsoon season.

The Madden-Julian Oscillation (MJO): MJO has been traversing the Western Pacific and Western Hemisphere in Phases 7 & 8, with limited impact on promoting moisture across the Indian Ocean basin. This MJO activity is unlikely to support the emergence of monsoon systems in the Bay of Bengal and Arabian Sea.

El Niño-Southern Oscillation (ENSO): As ENSO-neutral conditions persist, there is anticipation that La Niña may develop by mid-monsoon, potentially influencing the latter part of the season.

The alignment of ENSO and IOD parameters will be crucial in shaping the outcome of the 2024 monsoon, underscoring the importance of these climatic factors synergising effectively for favourable monsoon conditions.

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