It is the network of blue and green that provides climate resilience to Chennai city — blue of its wetlands and green of its patches of vegetation. However, this combination that had been protecting the city in the past is today under stress. The shrinking of blue and green has drastically reduced Chennai’s ability to deal with extreme weather events.
Just 15 months after a massive flood in November-December 2015 battered the city, the residents suffered a serious drought during the summer of 2017. Even while sporadic rains over the city since the onset of southwest monsoon in June 2017 have given respite from the drought, residents fear that there could be flooding with the northeast monsoon in the coming months.
Chennai, which receives up to 60% of its annual rainfall from the northeast monsoon that starts by mid-October, is expecting this year’s rains to be at least average or better than that. With the city’s ability to deal with intense rains decreasing, there are chances of waterlogging and floods. Even by its very nature, the northeast monsoon that brings rains to Chennai is different to the southwest monsoon. The northeast monsoon is mostly a string of depressions or cyclones, which bring heavy rain over a few days.
Having suffered heavily during the end-2015 floods, followed by a severe water shortage during the summer of 2017, the citizens of Chennai are apprehensive of facing floods in the coming weeks. The destruction caused by the 130 km per hour winds and rains of Cyclone Vardah in December 2016 only adds to this fear.
“Unless the city’s landscape is resilient, the people cannot be resilient,” explained Jayshree Vencatesan, managing trustee of Care Earth Trust. “We are only coping because there is no other choice. Each extreme weather event hits us hard.”
Image Courtesy: Vinoth Chander
Increase in built-up area
Using historical geo-spatial data, Care Earth Trust has developed maps that show the relationship of water bodies to built-up area in the city and the green cover within the city. As the blue (of the wetlands and water bodies) and green (vegetation cover) decreased in the past three decades over the Chennai metropolitan area, the red of built up area increased.
“Under the resilience framework, megacities are characterised as uncertain environments,” said Vencatesan. “We do not know whether climate change is causing the uncertainty or whether our messing up of the city’s environment is causing it.”
The development of the maps is part of a process to understand Chennai’s landscape and environment, according to her. There is inadequate data and insufficient understanding of the land use changes in the city and where population density is increasing. As a result, there is lack of clarity on the consequences of that change, especially with the ability to deal with extreme weather events. “We don’t have the detailed nuts and bolts understanding, and unless we have the data, our ability to deal with the situation is also not there,” Vencatesan added.
Even after suffering this summer’s drought, Chennai is apprehensive of the rains causing floods because of the 2015 experience, when between November 8 and December 4, there were five instances in which the city received more than 200 mm of rain in a continuous spell. The result of this downpour, combined with the city’s decreasing ability to absorb the water falling on its surface, led to the devastating floods, which resulted in the loss of more than 450 lives.
According to the annual estimates compiled by global reinsurance major Munich Re, the economic loss at USD 3.5 billion in and around Chennai due to the November-December 2015 flood was the second-most expensive event in the year.
Extreme rainfall events
There is evidence of increasing frequency of extreme rainfall events (EREs) not just in Chennai but also across India, even though their direct link with climate change is still considered tenuous. The 2012 special report on extreme events by the Intergovernmental Panel on Climate Change (IPCC-SREX) stated this for the first time to policymakers.
A recent study by a team of scientists led by M.K. Roxy from the Indian Institute of Tropical Meteorology, Pune, published in Nature, states that there is a three-fold increase in widespread EREs over central India between 1950 and 2015. This is despite a decrease in mean precipitation and also a decrease in the number of depression-related events.
Other studies by the Interdisciplinary Centre for Water Research (ICWaR) at the Indian Institute of Science, and the Ashoka Trust for Research in Ecology and the Environment (ATREE), have confirmed these findings for the Indian situation.
The ICWaR study even notes that the intensity of urban events is increasing vis-à-vis that of non-urban events.
Since there are indications of an increasing trend in EREs over Chennai, the network of wetlands and forests is important to provide resilience against such extreme weather events. These have been part of the natural landscape over which the city was built with rapid speed in recent decades.
Sponges on the city floor
For a coastal city with an almost level gradient, wetlands and forests serve as the points from which water recharges into the aquifer. They act like sponges on the city floor. The four rivers that run from west to east across the city — Araniyar, Kosasthalaiyar, Cooum and Adayar — serve as the drainage channels for excess storm water to flow into the sea. This network is complemented by the Buckingham Canal, which runs north to south across the city, and other smaller canals.
“The rivers and canals of Chennai have a clear role as flood control channels,” said Paul Appasamy, former director of the Madras School of Economics. “The natural hydrology of the city was forgotten and haphazard construction and development was done on the banks of the waterways obstructing their flow. This amplified the flooding of end-2015.”
There is an added obstruction to the flow of floodwater into the sea. Both Cooum and Adayar have a sand bank at their river mouth. Construction of the sea wall for the Chennai Port in the northern part of the city has resulted in coastal erosion north of the structure and accretion south of it. Thus, over recent decades, while the sea has eroded in north Chennai swallowing fishing hamlets and old temples, the Marina Beach has been growing in width. The very same process has been building sand banks, obstructing the flow of Cooum and Adayar into the sea.
Image Courtesy: S Gopikrishna Warrier
Loss of blue and green
It was the loss of the wetlands and forest patches that drastically reduced the city’s ability to soak excess rainwater and use it during the lean months. Since the opening of the TIDEL Park, an information technology hub, in 2000, the city has radiated out through a southern axis almost all the way to Mamallapuram. This was at the expense of a network of wetlands that ultimately drained into the Pallikaranai marsh, before opening out into the city at Kovalam.
According to Vencatesan, there were almost 50 water bodies that were linked to the Pallikaranai marsh through a network of cascading channels. Many of them have been built over, and also removed are the natural forests along their banks. Radial roads that connect the Old Mahabalipuram Road with the Chennai-Trichy highway have bisected the Pallikaranai marsh along multiple axes. Embankments were created across the marsh to build these roads, thereby disturbing the natural flow dynamics in the marsh.
“The wetlands in Chennai are like the arteries and veins of the city,” observed Ritesh Kumar, conservation programme manager, Wetlands International South Asia. “These have been under tremendous stress from development pressures in the past two decades and have been losing their ability to hold water when needed and control floods during heavy rains.”
He felt that the Wetland Conservation and Management Rules (2017), notified by the Union Ministry of Environment, Forests and Climate Change on September 26, 2017, can help conserve the remaining wetlands. “There are two points of strength for the new rules. First, it gives powers to the state governments to identify wetlands (which are not protected areas already) and develop conservation and management plans and implement them. Two, it stresses on the principle of wise use for these wetlands. Most of the wetlands are not no-go areas, and they can be conserved and managed on a sustainable manner through wise use.”
The flood of end-2015, followed by Cyclone Vardah and the drought this summer, has given Chennai residents a sense of what it would be like to live through a string of extreme weather events. In some locations there has been civil society action, supported by organisations and governmental institutions, to conserve and rejuvenate water bodies. Perhaps these could be the initial steps in the process to strengthen Chennai’s climate resilience where the network of blue and green holds the key.
This article was first published on India Climate Dialogue.
Source: The News Minute