Chennai Floods 2015

In November and December 2015, the annual North-East monsoon generated heavy rainfall in south India causing floods along the Coromandel Coast in Tamil Nadu, Andhra Pradesh and Pondicherry. Chennai and surrounding area were hardly hit by these floods. These floods caused displacement of around 18 Lakh people and claimed lives of around 500.

The El-Nino Link

A clear link between El Nino and North-East Monsoon is not yet established, but studies and observations reveal that El Nino normally results in excess rainfall in Tamil Nadu.  Years 2015 and 2015 are expected to witness the strongest El Nino ever and 2016 may be the hottest year on record. Scientists believe that it was the El Nino with record intensity this year that set stage for South India Floods. Most parts of India receive rains via the South-West Monsoon in summer. However, in winters, the North-East monsoon winds push back across the nation. This monsoon has a drying effect in most part of the country because they bring cool, dry air from interior Asia. But as these pass over the bay of Bengal, they pick up the moisture and precipitate along the coromandel coast. Chennai typically received its most of rains this way. Its worth note that El Nino causes deficient rains in India during South-West Monsoon, it becomes cause of heavy rains during North-East Monsoon.

Indian Ocean Dipole Link

The Indian Ocean Dipole is the difference in sea surface temperature between two areas- a western pole in the Arabian Sea and an eastern pole in the eastern Indian Ocean south of Indonesia. It is basically a miniature version of El Nino – La Nina phenomenon in Indian Ocean. It has negative and positive phases. A 2004 study linked Indian Ocean Dipole to the strength of the northeast monsoon. It found that a positive IOD was associated with heavier northeast monsoonal rains in South India. In 2015-16, IOD is  in a strongly positive mode and thus caused heavier rains this year in South India.

Unregulated urban planning and illegal construction

Unprecedented floods in Chennai were the direct result of unregulated urbanisation.  In Chennai, each of its lakes has a natural flood discharge channel which drains the spill over. However, development over many of these water bodies has blocked the smooth flow of water. A CSE study finds that Chennai had over 600 lakes in the 1980s, but a master plan published in 2008 showed only a fraction of them to be in a healthy condition. The area of 19 major lakes shrank from 1,130 hectares in the 1980s to around 645 hectares in the early 2000s, reducing their storage capacity. Further, the drains carrying surplus water have been encroached upon, water drains are clogged and require immediate desilting.

Centuries old Chennai has a natural network of drains and canals for flood waters to flow out and ponds and lakes to collect and store the water. These natural means of hydraulic balance in the city have fallen into disrepair, got silted and stuffed with garbage. Due to this, the water brought in by unusually heavy rains gets trapped. Thus, due to lack of adequate attention to natural water bodies in Chennai and other most urban areas of India has been the primary reason of havoc created by unusually heavy rains. This was coupled with filling up of canals and ponds by greedy developers; spread of slums across the water bodies (for example Adyar River in Chennai); Dredging the cooum and the Adyar river and absence of a rain water disposal system.

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