Why in news?
A new study found that although El Niño usually suppresses the Indian summer monsoon, it increases the likelihood of intense daily rainfall events. Understanding this paradox helps improve disaster preparedness.
What is El Niño?
- Definition: El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO). It involves abnormal warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean and weakening of the trade winds.
- Triggers: Positive sea surface temperature anomalies, westerly wind bursts and interactions with intraseasonal phenomena like the Madden–Julian Oscillation can initiate El Niño events. Climate change may influence their frequency and intensity.
- Frequency: El Niño events occur every 2–7 years, last 9–12 months and are monitored using the Oceanic Niño Index.
Impact on weather
- Global effects: El Niño often causes drought in Australia and Indonesia and heavy rainfall in Peru and the southern United States.
- Effect on the Indian monsoon: Traditionally, El Niño reduces overall monsoon rainfall, delaying onset and causing long dry spells. It can lead to droughts across India.
- New finding: Despite suppressing total rainfall, El Niño increases the probability of extreme daily downpours. The recent study found that during El Niño summers, the chance of very heavy rainfall (>250 mm in a day) rises by about 50 % across monsoon regions and even more in central India. Warm surface waters and stronger convective buoyancy make intense rainfall more likely.
Implications for disaster management
- Urban flooding: Cities like Mumbai and Chennai could experience short, intense deluges even during an overall weak monsoon. Drainage systems must be upgraded accordingly.
- Early warning systems: Weather agencies should monitor both seasonal rainfall forecasts and daily extreme rainfall probabilities. Localised alerts can save lives.
- Water management: States should plan for both drought and flood. Storing water during dry spells and managing reservoirs to absorb sudden inflows become critical.
Conclusion
El Niño is a complex climatic phenomenon that can simultaneously reduce seasonal rainfall and increase daily extremes. Policymakers must consider these nuanced impacts when preparing for monsoon seasons.