Reason found behind Chennai flood 2015

In News

  • A study by the University of Hyderabad and the Indian Institute of Technology Bombay suggests that the extreme El Nino that occurred in 2015 played an important role in Chennai’s heavy rainfall. After 1982 and 1997, the 2015 event also turned out to be an extreme El Nino event.

Reason Behind The Flood

  • The extreme El Nino conditions in 2015 and the warming trend in the Bay of Bengal contributed equally to the unprecedented heavy rainfall witnessed in Chennai for three days from November 30 to December 2, 2015, researchers have found.
  • The other factor could be warming of the Bay of Bengal off the coast of Tamil Nadu and Andhra Pradesh.

How scientists found the reason

  • A simple linear correlation analysis carried out by the scientists indicates that the Bay of Bengal sea surface temperature positively and significantly correlated with northeast monsoon rainfall.
  • The magnitude of correlations of northeast monsoon rainfall with El Nino conditions and the Bay of Bengal warming are nearly similar.
  • Based on sensitivity experiments they could conjuncture that about 21% of the intensity of the extreme Chennai rainfall can be attributed to the extreme El Nino conditions.

“Experiments suggest that changes in local sea surface temperature seem to be stronger than local atmospheric changes,” Dr. Ashok says.

El Nino

El Niño  is the warm phase of the El Niño Southern Oscillation (commonly called ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including off the Pacific coast of South America.

El Niño Southern Oscillation refers to the cycle of warm and cold temperatures, as measured by sea surface temperature, SST, of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.

The cool phase of ENSO is called “La Niña” with SST in the eastern Pacific below average and air pressures high in the eastern and low in western Pacific. The ENSO cycle, both El Niño and La Niña, cause global changes of both temperatures and rainfall.

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