Chennai floods due to impact of climate change: CSE

An Indian green body today said that the floods in Chennai are an impact of climate change and the "unprecedented deluge" that the city has witnessed is a reminder of increasing frequency of such freak weather events across the Indian subcontinent.

The Centre for Science and Environment (CSE) said that Chennai could have fared better if it had protected and preserved its natural water bodies and drainage channels.

"We have repeatedly drawn attention to the fact that our urban sprawls such as Delhi, Kolkata, Mumbai, Chennai, Srinagar and others have not paid adequate attention to the natural water bodies that exist in them," said CSE director general Sunita Narain.

"In Chennai, each of its lakes has a natural flood discharge channel which drains the spillover. But we have built over many of these water bodies, blocking the smooth flow of water. We have forgotten the art of drainage. We only see land for buildings, not for water," she said.

She said that 'Down To Earth', the science and environment fortnightly that CSE helps publish, had earlier reported on the destruction of wetlands in Chennai.

CSE said that a number of cities including Chennai are both water-scarce as well as prone to flooding.

"Both problems are related – excessive construction which leads to poor recharge of groundwater aquifers and blocking of natural drainage systems. While Chennai has been struggling to meet its water needs and has been even desalinating sea water at a huge expense, it allowed its aquifers to get depleted," said Sushmita Sengupta, deputy programme manager with CSE's water team.

CSE's research shows that Chennai had more than 600 water bodies in the 1980s, but a master plan published in 2008 said that only a fraction of them are in healthy condition.

According to records of the state's Water Resources Department, the area of 19 major lakes has shrunk from a total of 1,130 hectares (ha) in the 1980s to around 645 ha in the early 2000s, reducing their storage capacity.

The drains that carry surplus water from tanks to other wetlands have also been encroached upon.

The analysis also shows that the stormwater drains constructed to drain flood waters are clogged and require immediate desiltation and Chennai has only 855 kms of stormwater drains against 2,847 kms of urban roads.

CSE said that the rains in Chennai have broken a 100-year record (374 mm in just 24 hours).

In November, the city had received 1,218 mm of rain, which was almost three times more than the average the city receives (407 mm), it said.

Scientific research has already linked such intense weather phenomena to a changing climate and IPCC's fifth Assessment Report clearly says that frequency and intensity of such excessive rainfall events will increase in future.

CSE said that a 2006 study by the Indian Institute of Tropical Meteorology (IITM) in Pune had said that extreme precipitation events were increasing in frequency and intensity in India during the period 1950 to the 2000s.

CSE's climate change experts point out that while detailed attribution studies needed to be done to find out more links between the Chennai catastrophe and climate change, existing scientific studies do establish the possibility of a connection.