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India Braces for La Niña’s Return
Context: Weather experts have warned that India could face an intense cold wave during the winter of 2025-26 (December-January). This prediction is significant especially after the Triple Dip La Nina (2020-23).
La Niña is the “cool phase” of the El Niño-Southern Oscillation (ENSO) cycle—a natural climate phenomenon marked by unusually cold sea surface temperatures in the central and eastern tropical Pacific Ocean. It happens when stronger-than-normal trade winds push warm water westward, causing cool, nutrient-rich water to upwell in the east.
How Does La Niña Impact Indian Weather?
La Niña’s influence on Indian weather is delivered through “teleconnections,” or long-distance atmospheric links.
- Stronger Winter Monsoon (North-East Monsoon): For peninsular India, particularly Tamil Nadu, Andhra Pradesh, and Kerala, La Niña years often bring a good North-East Monsoon, leading to higher rainfall between October and December.
- Colder Winter Temperatures over North India: This is the primary impact highlighted in the current forecast. The mechanism involves:
- Change in Jet Stream Patterns: La Niña tends to alter the path of the sub-tropical westerly jet stream, a high-altitude wind current that greatly influences winter weather in North India.
- Deeper Troughs and More Western Disturbances: The jet stream develops deeper north-south waves (troughs). These troughs scoop out cold air from higher latitudes and pull it down towards northern parts of the Indian subcontinent.
- Increased Frequency of Cold Wave Conditions: This influx of cold, dry air leads to a higher number of cold wave days, where minimum temperatures drop significantly below normal. Dense fog and prolonged cold spells are also more common.
- Positive Impact on Summer Monsoon: La Niña has a strong correlation with above-average rainfall during India’s Southwest Summer Monsoon (June-September). The cooling in the Pacific shifts convection patterns, strengthening the monsoon circulation.
- Air quality trends:
- Poor quality in Peninsular India: Relatively slower winds near the surface, traps pollutants and notably increases PM2.5 concentration.
- Improved Air quality in Northern India: Weaker western disturbances with absence of rain and clouds and faster ventilation led to a significant improvement in air quality in the North. However, contrary observations can also be registered with interplay of multitude factors.
