The weak La Niña event that emerged in December 2024 is likely to be short-lived, according to the latest update from World Meteorological Organisation (WMO).
La Niña represents abnormal warming of West Pacific – of which South China Sea is a marginal sea – that lies close to South-East Asia and the Indian subcontinent. Warming of waters occasions lower pressure, rising motion of air, accelerated evaporation, formation of clouds, storms and heavy rain. La Niña has traditionally been considered a good augury for Indian monsoon.
Wind, pressure patterns
In WMO parlance, La Niña refers to large-scale cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in wind, pressure and rainfall patterns. Typically, La Niña brings climate impacts that are opposite of El Niño, especially in tropical regions. In an El Niño, warming happens to the east of the Pacific, shifting evaporation shifts to coasts of the Americas. Air sinks (instead of rising) over west Pacific, leading to higher pressure that does not allow clouds to form. El Niño has most translated into dry spells/droughts in India, though with honourable exceptions.
Massive Pacific Ocean
The massive Pacific Ocean lies between the continents of Asia and Australia on the west, and North America and South America in the east. Separation between the Pacific and Indian Ocean lies a line of islands extending eastward from Sumatra in Indonesia, not too far from the Andaman & Nicobar Islands in the Bay of Bengal.
Pacific accounts for a third of surface of globe and almost 80 per cent of the water volume of all oceans. Its area exceeds that of the whole land surface of the globe. Its size allows it to store and distribute vast amounts of heat, driving major ocean currents. These currents in turn impact weather patterns around the world, particularly through El Niño and La Niña phenomena.
Pacific’s marginal seas
This explains disproportionate impact that it imparts on weather and climate in India, especially annual south-west monsoon. Among Pacific’s marginal seas are South China Sea that lies next door to the Bay, Yellow Sea and East China Sea. Forecasts from the WMO Global Producing Centres for Seasonal Prediction indicate current cooler than average sea-surface temperatures in the equatorial Pacific are expected to return to normal. There is a 60 per cent probability conditions will shift back to ‘neutral’ (neither El Niño nor La Niña) during March-May 2025, increasing to 70 per cent for April-June 2025.
Neutral conditions
It is likely ‘neutral’ conditions may prevail by the time the monsoon sets in over India. Years in which a prevailing weak La Niña has transitioned to ‘neutral’ may not inspire confidence since rainfall received has ranged from below-normal to just normal. But previews by various global models for 2025 monsoon indicates normal rainfall, with local drivers likely coming into play. Probability of El Niño developing is negligible during March to June), the WMO said. But uncertainty in forecasts is higher than usual due to spring predictability barrier, a well-known challenge forecasts of El Nino/La Niña during this time of the year.
Important tool
“Seasonal forecasts for El Niño and La Niña and associated impacts on weather and climate patterns are an important tool to inform early warnings and one of a wide suite of services offered by the WMO to support decision-making,” said Celeste Saulo, Secretary-General, WMO. “These forecasts translate into millions of dollars worth in economic savings for key sectors like agriculture, energy and transport, and saved thousands of lives over the years by enabling disaster risk preparedness,” she added.
Climate change challenge
Impacts of La Niña and El Niño on climate patterns are taking place in broader context of human-induced climate change, which is increasing global temperatures, exacerbating extreme weather and climate, and impacting seasonal rainfall and temperature patterns. January 2025 was the arrest January on record despite weak La Niña conditions present since December 2024.
