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Monsoon and ENSO Forecast for 2025
Context:
India eagerly awaits the summer monsoon forecast each year, with a particular focus on whether it will be a ‘normal’ monsoon, often linked to the status of El Niño or La Niña events.
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- The monsoon’s fate is often linked to El Niño and La Niña events, although these phenomena account for only about 60% of deficit and surplus years.
- Sea Surface Temperature (SST) patterns in the tropical Pacific Ocean have evolved unpredictably since early 2024.
El Niño and Monsoon in 2023
- El Niño forecasts in early 2023 were accurate, yet the 2023 monsoon was deemed ‘normal’ in terms of total seasonal rainfall.
- However, ‘normal’ monsoon did not equate to even distribution:
- Heavy spells occurred in several states.
- Deficits were recorded in Karnataka, Kerala, Uttar Pradesh, West Bengal, and the Northeast.
- Global Warming’s Influence on El Niño: The 2023 El Niño was unusual:
- Expected cooling in the far western Pacific did not occur.
- Instead, weak warm SST anomalies appeared, attributed to:
- Global warming
- El Niño-induced variations
Unexpected Shifts in SST Patterns in 2024
- Early 2024 forecasts predicted a strong La Niña in the latter half of the year.
- Initial cold SST anomalies appeared in the far eastern tropical Pacific, signalling La Niña.
- However, anomalies shifted westward towards the international dateline.
- Warm SST anomalies emerged in the Far East by early summer 2024, contradicting expected La Niña patterns.
Unusual Wind Patterns
- Strong easterly anomalies were present in the central-western tropical Pacific.
- Simultaneously, westerly anomalies emerged in the far eastern tropical Pacific.
- The unusual combination persisted, complicating climate predictions.
The Role of Central Pacific El Niño
- Historically, the reverse SST pattern was more common, known as the Dateline El Niño or Central Pacific El Niño.
- Unlike La Niña, which has a dominant pattern, El Niño has two ‘flavours’:
- Warm SST anomalies in the eastern Pacific.
- Warm SST anomalies in the central Pacific.
Uncertainty Around the 2025 ENSO State
- The current unusual SST patterns could be linked to record-high temperatures from 2023-2025.
- Lack of cooling in the far eastern tropical Pacific prevents ocean heat uptake, leading to atmospheric heat accumulation.
Possible Cause: ENSO Transition Mode (ETM)
- A study identified a natural climate variability mode in the Southern Pacific that influences tropical Pacific wind patterns.
- The ENSO transition mode (ETM) was unfavourable for transitioning from El Niño (2023-24 winter) to La Niña (2024 summer).
- ETM-induced wind anomalies likely prevented the anticipated strong La Niña in 2024.
Uncertainty in Future Climate Predictions
- The relationship between ENSO and the monsoon has changed over recent decades.
- Global mid-latitude temperature anomalies and jet stream variations influence: Monsoon patterns, Pre-monsoon cyclones, Timing of monsoon onset.
Implications for India’s Agriculture and Policy
- The unpredictability of monsoon forecasts keeps Indian farmers on edge.
- Reliable forecasting remains crucial for:
- Agricultural planning
- Disaster management
- Government policy decisions
- The India Meteorological Department (IMD) and climate scientists continue efforts to improve forecast accuracy.
- However, managing expectations is as challenging as mitigating the risks of monsoon variability and early heat waves in 2025.
Way Forward
- Given ongoing climate uncertainties, India must:
- Enhance resilience to monsoon variability.
- Improve climate adaptation strategies.
- Invest in better forecasting technology.
- As always, while we hope for the best, we must prepare for the worst.
What is El Niño–Southern Oscillation (ENSO)?
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- ENSO is a recurring climate pattern where temperatures in the central and eastern tropical Pacific Ocean fluctuate every 3 to 7 years. Surface waters across a large area warm or cool by 1°C to 3°C, affecting rainfall in the tropics and influencing the global weather system.
- Though ENSO is a single climate phenomenon, it has 3 phases : El Niño , La Niña and ENSO-neutral.
- El Niño :
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- It causes warming of the ocean surface, resulting in above-average sea surface temperatures (SST) in the central and eastern tropical Pacific Ocean.
- This leads to reduced rainfall over Indonesia and increased rainfall across the central and eastern tropical Pacific Ocean.
- The usual easterly winds along the equator weaken or may reverse, occasionally becoming westerly.
- The warmer the ocean temperature anomalies, the stronger the El Niño (and vice-versa).
- La Niña :
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- This entails cooling of the ocean surface, causing below-average sea surface temperatures (SST) in the central and eastern tropical Pacific Ocean.
- Over Indonesia, rainfall tends to increase while decreasing over the central and eastern tropical Pacific Ocean.
- The normal easterly winds along the equator intensify further.
- The cooler the ocean temperature anomalies, the stronger the La Niña (and vice-versa).
- Neutral Phase: This phase occurs when neither El Niño nor La Niña is dominant. Sea surface temperatures (SSTs) in the tropical Pacific are generally near average.
