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.
What is El Nino?
El Nino is the warm phase of the El Nino Southern Oscillation .El Nino is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.
What went wrong?
El Nino generally causes less than normal rainfall in the case of the southwest monsoon. In contrast, it brings about above-normal rainfall during the northeast monsoon. This is because of the difference in seasonal wind patterns between the two monsoons.
- Another factor that seems to have played an important role is the consistent warming of the Bay of Bengal off the coast of Tamil Nadu and Andhra Pradesh.
- Based on sensitivity experiments it is concluded that about 21% of the intensity of the extreme Chennai rainfall can be attributed to the extreme El Nino conditions.
Unregulated urban planning and illegal construction
Problem was also with poor town planning of the town.There was improper design and maintenance of drainage systems. The canals were blocked and there was no way the excess rain could be drained.
- Chennai Corporation ignored September 2015 warnings of above-average monsoonal rains issued by the Indian Meteorological Department.
- The 2014 CAG report said the defective planning of flood control projects caused delays and increased costs.
- Experiments suggest that changes in local sea surface temperature seem to be stronger than local atmospheric changes.
- It remains to be seen if this kind of contribution from the tropical Pacific to extreme rainfall during the northeast monsoon happens only during extreme El Nino or whether normal El Ninos too can cause it.