south-west monsoon Current Affairs

Scientists discover reasons behind 2015 Chennai Floods

A study conducted by the University of Hyderabad and the Indian Institute of Technology – Bombay has found out that the extreme El Nino conditions and warming of the Bay of Bengal had resulted in unprecedented heavy rainfall in Chennai for three days between November 30th to December 2nd in 2015.

Salient Findings

El Nino usually causes less than normal rainfall in the case of south-west monsoon. However, it does the reverse in the case of the northeast monsoon. It causes above-normal rainfall during the northeast monsoon. This is due to the difference in seasonal wind patterns between the two monsoons.

The researchers had carried out a simple linear correlation analysis that points out that the sea surface temperature at the Bay of Bengal is positively correlated with northeast monsoon rainfall. It has been found out that the magnitude of correlations of northeast monsoon rainfall with El Nino conditions and the Bay of Bengal warming to be almost same.

Based on several experiments, the scientists have attributed around 21% of the intensity of the extreme Chennai rainfall to the extreme El Nino condition

The consistent warming of the Bay of Bengal off the coast of Tamil Nadu and Andhra Pradesh is also considered as an important factor for the floods by the scientists.

However, scientists are yet to ascertain whether the contribution from the tropical Pacific to extreme rainfall during the northeast monsoon occurs only at the time of extreme El Nino or whether normal El Ninos too are capable of causing them.


El-Nino is a weather phenomenon, during which temperature at sea surface is warmer than normal sea-surface temperatures. El Nino is a warming of the Pacific Ocean between South America and the Date Line, centred directly on the Equator, and typically extending several degrees of latitude to either side of the equator. It accompanies high air surface pressure in the western Pacific. El Niño occurs when tropical Pacific Ocean trade winds die out and ocean temperatures become unusually warm