The La Niña Effect: Why an Early, Sharper Winter is Gripping Indian Cities 

Driven by the return of La Niña conditions in the Pacific Ocean, major Indian cities including Delhi, Mumbai, and Bengaluru are anticipating an earlier and colder-than-usual winter season. This climate phenomenon, marked by a cooling of Pacific waters, strengthens the systems that funnel colder air into the Indian subcontinent.

While expected to be weak and short-lived, its influence will vary regionally: northern plains like Delhi will face the core chill with sharper temperature drops and increased fog, coastal Mumbai will experience a more pronounced and less humid coolness, and elevated Bengaluru will see an intensification of its characteristic pleasant winter. However, this forecasted cold snap exists within the larger context of global warming, which may moderate its intensity and lead to uneven temperature patterns, illustrating the complex interplay between natural climate cycles and human-induced climate change.

The La Niña Effect: Why an Early, Sharper Winter is Gripping Indian Cities 

As the last vestiges of the monsoon humidity fade, a new seasonal narrative is taking shape across India. This year, the familiar transition into winter is set to be different. Meteorologists are pointing to a significant climatic shift happening thousands of kilometres away, one that promises to deliver an earlier and more pronounced chill to the air, from the northern plains of Delhi to the coastal warmth of Mumbai and the pleasant climes of Bengaluru. 

The cause? The return of a familiar yet powerful player in global weather patterns: La Niña. But this isn’t just a simple story of a “colder winter.” It’s a complex tale of atmospheric teleconnections, regional nuances, and the ever-present, moderating influence of global climate change. 

The Pacific’s Chilly Breath: Unpacking the La Niña Phenomenon 

To understand why Mumbai might need a sweater sooner than usual, we must first look to the central equatorial Pacific Ocean. Here, the Earth’s most significant climate engine, the El Niño-Southern Oscillation (ENSO), operates. It cycles through three phases: the warm El Niño (Spanish for “The Little Boy”), the cool La Niña (“The Little Girl”), and neutral conditions. 

La Niña is essentially the planet’s air conditioner kicking into overdrive in a specific region. It is characterized by a strengthening of the trade winds, which push warm surface water westward towards Indonesia and the Philippines. In its place, deep, nutrient-rich cold water wells up from the ocean depths along the coast of South America. 

This seemingly regional event creates a massive domino effect across the globe. The accumulation of warm water in the western Pacific fuels increased cloud formation and rainfall in that region. This rearrangement of heat and moisture in the atmosphere alters the trajectory of jet streams—the high-altitude, fast-flowing air currents that act as steering currents for our weather. 

For the Indian subcontinent, a classic La Niña winter often means a more robust and southward-shifted jet stream. This configuration acts as a funnel, channelling colder, drier air from the Siberian high-pressure system directly into the heart of North India. The result? An earlier onset of winter, a greater frequency of cold waves, and denser, more persistent fog as the cold air traps moisture and pollutants close to the ground. 

A Familiar Guest with an Uncertain Temperament 

What makes this year particularly noteworthy is the frequency of La Niña’s visits. The confirmation of its emergence in September 2025 marks the fifth time in six years we’ve entered this cool phase. This run of consecutive La Niñas is unusual and has scientists closely monitoring its long-term implications. 

However, a crucial caveat tempers the forecast. The US National Oceanic and Atmospheric Administration (NOAA) has indicated that this year’s La Niña is expected to be weak and short-lived, likely persisting only through the December-February window. This “weak” designation is key. It suggests that while the pattern of a colder winter will be present, its intensity may be muted compared to a strong La Niña year. Think of it as a guest who arrives early but doesn’t overstay their welcome with extreme behaviour. 

City-by-City: Decoding the Winter Forecast 

The impact of La Niña is not a uniform blanket of cold thrown over the entire country. Its effects are filtered through local geography, creating distinct experiences for different urban centres. 

1. Delhi-NCR and the Northern Plains: Bracing for the Core Chill

• What to Expect: Cities like Delhi, Chandigarh, Lucknow, and Amritsar will feel the brunt of La Niña’s influence. The region can anticipate: 

• An Earlier Onset: A perceptible drop in minimum temperatures is likely to begin in late October or early November, rather than mid-November. 

• Colder Spells: The core winter months of December and January could see nighttime temperatures dipping 2-4 degrees Celsius below the seasonal average. 

• Fog and Travel Disruption: The combination of cold air and moisture from the western disturbances creates a perfect recipe for dense morning fog. This will have a significant knock-on effect, disrupting flight and train schedules and making road travel hazardous, particularly on highways. 

2. Mumbai and the West Coast: A Respite from the Relentless Humidity

• What to Expect: For Mumbaikars accustomed to a mild, often humid winter, this season could offer a more genuine coolness. 

• Cooler, Drier Nights: The real feel will change. Instead of just a slight drop in temperature with high humidity, the “December nip” in the air will be sharper and more pronounced, especially during the early mornings and late evenings. 

• The “Why”: La Niña’s large-scale circulation patterns can lead to clearer skies and calmer winds over the peninsula. This allows for more effective “radiational cooling” at night, where the Earth’s surface loses heat rapidly into the atmosphere. The result is a more comfortable and distinct winter experience, even if daytime highs remain relatively stable. 

3. Bengaluru and the Southern Plateau: Where the “Air Conditioner” Truly Shines

• What to Expect: Bengaluru, with its elevated topography, is perfectly positioned to experience a quintessential La Niña winter. 

• Prolonged Pleasantness: The city famous for its year-round pleasant weather will see its winter season intensify. Expect a longer stretch of cold mornings, with minimum temperatures potentially reaching the 12-14°C range more frequently. 

• Crisp Mornings, Sunny Days: The pattern of cold, crisp mornings giving way to bright, sunny afternoons will become the norm. This is the kind of weather that defines Bengaluru’s winter charm, and La Niña is set to turn up the dial. 

The Climate Change Paradox: A Chilly Mask on a Warming Planet 

This forecast for a cold winter might seem at odds with the relentless headlines about global warming. This is the central paradox that meteorologists are grappling with. The World Meteorological Organization (WMO) has been clear: while natural climate phenomena like La Niña and El Niño cause significant year-to-year variability, they are now playing out against the backdrop of human-induced climate change. 

Think of it this way: Climate change is the soundtrack, while La Niña is the current song. The overall trend is one of warming—2025 is still on track to be one of the warmest years on record globally. La Niña simply provides a temporary, regional “cooling track” on top of that hotter baseline. 

This interplay can lead to “weather whiplash”—intense but short-lived cold snaps within a warmer-than-average season. It also means that while northern India shivers, other parts of the world might be experiencing record heat. The cold in Delhi does not disprove the warming of the planet; it is a complex, localized expression within a much larger and warmer system. 

Beyond the Chill: The Ripple Effects of a Colder Winter 

A shifting winter pattern has consequences that extend far beyond our choice of clothing. 

• Agriculture: For the Rabi (winter) crop season, a colder winter can be a double-edged sword. While moderate cold is beneficial for crops like wheat, an intense and prolonged cold wave can damage harvests and stunt growth, potentially impacting yields. 

• Health: Colder temperatures and increased fog can exacerbate respiratory illnesses like asthma and bronchitis. The poor air quality in cities like Delhi, combined with dense fog (smog), creates a serious public health challenge. 

• Energy Consumption: As the mercury drops, the demand for heating, especially in North India, will spike. This puts a strain on power grids and increases reliance on fossil fuels and wood-burning, which in turn can worsen air pollution. 

In conclusion, the return of La Niña is setting the stage for a winter that demands our attention. It promises a sharper, more defined cold season across India’s major cities, offering a temporary respite from the overarching trend of warming. Yet, it also serves as a powerful reminder of the intricate dance between natural climate cycles and human-driven change. As we unpack our winter wear a little earlier this year, we are not just preparing for the cold; we are witnessing a real-time lesson in the complex, interconnected, and changing climate of our planet.