As Northwest India entered October, coinciding with the annual festive season of Dussehra, people began to feel a chill in the air, especially at night. Many started reducing their fan speeds and wrapping themselves in sheets. This change in temperature reminded some of October 2020 when Delhi experienced its coldest month since 1962, with a mean minimum temperature of 17.2°C.
In contrast to the warmest October recorded by the India Meteorological Department (IMD) last year, this year’s unusual cold in October suggests a potentially colder winter ahead, one of the coldest in decades. This October, weather scientists observed that Delhi’s maximum temperatures have mostly been lower than normal, while minimum temperatures have remained above average.
In the second week of the month, the season’s first spell of western disturbance impacted the Northwest region, resulting in heavy snowfall in the higher reaches of the Himalayas including Jammu and Kashmir, Ladakh, Himachal Pradesh, and Uttarakhand. Cold winds sweeping across the plains caused both maximum and minimum temperatures to drop to record lows for a week. The maximum temperatures dipped to the range of 26°C to 30°C, while minimum temperatures ranged from 18°C to 19°C for over 10 days, in contrast to the average mean maximum temperature of 31°C to 33°C and an average mean minimum temperature of 19°C to 22°C during October.
The sudden and consistent drop in temperatures led to concerns about a colder winter arriving alongside heightened air pollution levels in Northern India, particularly in the Indo-Gangetic plain.
People’s apprehensions are not without reason. Global meteorological agencies, including the IMD, have warned of a higher likelihood of a potential La Niña event, characterised by cooler-than-average temperatures in the central and eastern tropical Pacific Ocean region. This potential La Niña could result in colder and more severe winters for northern India, prolonging cold spells.
Scientists say La Niña enhances the influence of western disturbances and westerly winds over North India. Moreover, colder air masses from higher latitudes like Siberia and Central Asia penetrate further south into northern India due to a north-south trough in the upper atmosphere, the Himalayan region is expected to experience heavier snowfall. This could lead to disruptive cold winds affecting the daily lives of millions.
Besides, La Niña is also associated with a wetter-than-normal northeast monsoon season, particularly affecting Tamil Nadu, Kerala and coastal Andhra Pradesh, while central India may experience drier conditions.
In its latest bulletin, the IMD declared a higher possibility of La Niña conditions this coming winter. It reported the presence of neutral El Niño-Southern Oscillation (ENSO) conditions over the equatorial Pacific region and noted that predictions from its model, Monsoon Mission Climate Forecast System (MMCFS) and other global climate models indicate an increased likelihood of La Niña during the upcoming months. The US National Oceanic and Atmospheric Administration (NOAA) and the World Meteorological Organization (WMO), have already announced the return of La Niña in September 2025. However, the European Copernicus Climate Service has predicted weaker La Niña conditions, which may lead to a warmer winter or conditions similar to previous years.
What is La Niña?
La Niña is a cooler phase of the broader El Niño-Southern Oscillation (ENSO), a natural climate phenomenon. The ENSO has three phases: El Niño, Neutral, and La Niña. The natural cycle swings between warmer and cooler seawater in a region along the equator in the tropical Pacific Ocean. The natural phenomenon occurs periodically every two to seven years, causing a ripple effect on the global climate, increasing the chance of floods, excess rain, drought, snowfall and other chaotic weather conditions. It affects the Indian monsoon and winter.
El Niño – During El Niño, warm surface waters shift toward the central/eastern tropical Pacific, which alters large-scale air circulation. This shift causes lesser rainfall in areas that receive normal rainfall, and some areas often get drier or wetter. For instance, it causes heavier rainfall and flooding in South American Countries like Peru, Ecuador while India and Southeast Asia and Australia tend to get weaker monsoon rainfall, which increases the chance of drought and water shortages. In Africa, it causes wetter East Africa while drier Southern Africa.
La Niña – La Niña is the opposite of the El Nino phenomenon. The ocean surface in the central/eastern tropical Pacific is cooler than normal, so its impact is quite different from El Niño. It causes essentially above-normal rainfall, increased flooding risk, especially in the Indian subcontinent and Australia, wetter in Southern Africa and drier in East Africa and South American countries like Peru and Ecuador.
Neutral ENSO – This is the “baseline” or “normal” state of the tropical Pacific. Trade winds blow east to west across the equatorial Pacific. In this process, warm water is pushed towards the western Pacific coasts, such as Indonesia and Australia, while cooler water is pushed towards the eastern Pacific coast of South America, maintaining atmospheric balance. In this phase, globally weather patterns are relatively ‘normal’ for the region, and no extreme weather events generally take place.
However, WMO terms the increasing frequency of El Niño and La Niña due to climate change. It states that naturally occurring climate events, such as La Niña and El Niño, occur within the broader context of human-induced climate change. It is increasing global temperatures, exacerbating extreme weather, and impacting seasonal rainfall and temperature patterns.
The recent ‘warm blob’ phenomenon in the North Pacific region — extending from the east coast of Asia to the west coast of North America– is a case in point. The region registered record warming in the past decade but 2025 is markedly higher than recent years between July and September. Scientists think the extra heat, called the ‘warm blob’, may have the opposite effect in the UK and Europe, possibly leading to a colder winter.
La Niña does not always bring cold winters
It would be simplistic to expect La Niña years to automatically produce colder winters. Recent evidence indicates otherwise. For instance, winters in 2023 and 2024 were warmer, despite both being La Niña or La Niña-affected years. The overall temperature anomalies across the country were positive. In 2024, the mean temperature anomaly for the Indian winter (January–February) was +0.37°C, and in 2023, it was +0.83°C. Even in 2022, which was a La Niña year, the anomaly was close to normal at −0.04°C nationally.
A senior scientist at the Indian Institute of Tropical Meteorology (IITM) emphasized the need to re-evaluate recent evidence before simplifying the connection between La Niña and harsher winters. “From 2020 to 2024, despite an extended La Niña phase (September 2020 to March 2023, and again in winter 2024), most parts of India experienced above-normal winter temperatures. Warmer conditions were noted during January–February 2021, October–December 2021 and 2022, and January–February 2023,” said the scientist.
Years such as 2005, 2007, 2010, 2011, and 2012 showed a direct correlation with La Niña influence, as temperatures dropped further below the average from 1991 to 2020. However, in years like 1995, 1998, 1991, 1999, 2000, 2010, and during recent years such as 2016, 2017, 2020, 2021, 2022, 2023, and 2024, the winter temperatures were hardly affected by La Niña, instead showing a positive anomaly.
“In recent years, there has been no direct connection between harsher winters and La Niña, largely due to India’s geographical features, such as the Himalayas, which block much of the polar winds,” said Dr O P Sreejith, Scientist and Head of the Climate Monitoring and Prediction Group at IMD.
