Source: DH
Context: A new study shows El Niño raises the probability of extreme daily rainfall across central India by nearly 50%, even though it suppresses overall monsoon rainfall, raising fresh concerns about flood hazards and climate resilience planning.
About El Niño:
What It Is?
- El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) phenomenon.
- It refers to the unusual warming of sea surface temperatures in the central and eastern tropical Pacific Ocean, disrupting global weather patterns.
How It Forms?
- Normally, trade winds push warm water westward towards Indonesia, allowing cold water upwelling off South America.
- During El Niño, trade winds weaken, warm water shifts eastwards, deepening the thermocline and suppressing nutrient-rich upwelling.
- This alters Pacific jet streams and global atmospheric circulation, creating weather anomalies worldwide.
Factors Favouring El Niño:
- Weakening of easterly trade winds (natural variability).
- Positive sea surface temperature anomaly (≥0.5 °C above normal for ≥5 consecutive overlapping 3-month seasons).
- Influence of westerly wind bursts, Madden–Julian Oscillation (MJO), and background global warming trends.
Key Features:
- Periodic occurrence: Every 2–7 years, irregular cycle.
- Measured by ONI (Oceanic Niño Index) using Sea Surface Temperature anomalies.
- Global teleconnections: Alters rainfall, storm tracks, fisheries, and temperature worldwide.
- Often accompanied by droughts in Indonesia & Australia and floods in South America.
Impact on Indian Monsoon
- Seasonal Rainfall: Generally, suppresses SW monsoon → droughts more likely
- Rainfall Distribution: Reduces number of rainy days, but increases intensity of extreme rain events in wetter regions (as per new study).
- Monsoon Onset/Withdrawal: Often causes delayed onset and erratic withdrawal.
