Syllabus: Disaster and its management
- Tropical cyclones that originate near the Equator, while being devastating, have been unusually subdued in recent decades.
- Last major cyclone in India was Cyclone Okchi, which devastated parts of Kerala, Tamil Nadu and Sri Lanka in 2017.
- A combination of global warming and a cyclical event called the Pacific Decadal Oscillation (PDO) that repeats every 20 to 30 years, could make such cyclones more frequent in the coming years.
- The number of such equatorial-origin cyclones was 43% less between 1981 – 10 compared to 1951 – 80, and this was because the PDO was in a ‘warmer’ or positive phase.
- El Nino: A warming of the Central Equatorial Pacific – reduced rainfall over India
- La Nina: cooler than normal temperatures – linked to excessive rainfall.
- This pattern is collectively called the El Nino Southern Oscillation (ENSO) phenomenon
- repeats in the Pacific over two to seven years.
- Positive and negative phase of ENSO can be detected much faster than PDO.
- In 2019, the PDO entered a cooler, negative phase and if it remains so, could mean more tropical cyclones in the post-monsoon months that originate near the equator – It’s usually rare for cyclones to form near the Equator but when the waters are warm, they can gain more moisture and rise in intensity.
- An El Nino is developing in the Pacific, the effects of which are manifested in central and southern India, which have recorded rainfall deficits of 7% and 17%, respectively.
- PDO: corresponds to a warmer than average Western Pacific Ocean and relatively cooler Eastern Pacific
- plays out over much longer time scales.
- a ‘positive’ or ‘warmer phase’ of a PDO can be known only after several years of measuring ocean temperatures and their interaction with the atmosphere.