- According to a recent study, new evidences have been found that suggest that winter rainfall in India is heavily influenced by the variability in sea-surface temperatures of Pacific Ocean.
Variability in sea-surface temperatures of Pacific Ocean: El Niño-Southern Oscillation (ENSO)
- The El Niño-Southern Oscillation (ENSO) is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean.
- On periods ranging from about three to seven years, the surface waters across a large swath of the tropical Pacific Ocean warm or cool by anywhere from 1°C to 3°C, compared to normal.
- El Niño:
- A warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean.
- La Niña:
- A cooling of the ocean surface, or below-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean.
Effect of El Niño on monsoon
- On Summer Monsoon:
- The summer monsoon of India, brings in about 70% of annual rainfall in the country, is heavily influenced by the El Niño Southern Oscillation (ENSO).
- A warmer than usual Pacific Ocean, off the coast of South America, is known to suppress the monsoon rainfall in India.
- On Winter Monsoon:
- The winter monsoon, also called as the northeastern monsoon brings in more than 50% of the annual rains in coastal Andhra Pradesh, Rayalaseema, Tamil Nadu, south interior Karnataka, and Kerala comes during these winter months.
- ENSO is known to have an impact on the winter monsoon as well but is weaker and opposite.
- The warming of sea-surface waters is seen to help winter rainfall rather than suppressing it.
- The impact varies in time and space. The influence is weaker in October and stronger in November and December.
Note: The rainfall over southeastern peninsular India and Sri Lanka is strengthened with warming ocean, but is diminished over Thailand, Vietnam and the Philippines.
- The study on stalagmites (mineral deposits, mainly limestone, in caves) of the Mawmluh Cave, near Cherrapunji was done by the researchers.
- The solid stalagmite structures of the cave are the result of slow and steady water dripping in the caves, and contain several thin layers of different kinds of minerals that that get picked up while the water is flowing.
- By studying the composition of these stalagmites, scientists can deduce the amount of rainfall and source of the water of rainfall (local or other place) that could have happened over the caves in the past.
- Using such techniques, the researchers could estimate local variations in rainfall in the past, and then correlate it with old ocean records of the Pacific Ocean.
- The stalagmites indicate the recurrence of intense, multi-year droughts in India over the last several.
- The stalagmite records from monsoon regions, including India, are vital to understanding past variability in the global climate system and the underlying reasons for this variability.
- This new connection could help in predicting the rainfall during the winter months in India.