One important area of recent research in climate change science relates to understanding extreme events, including extreme rainfall events, of the kind that Chennai experienced on December 1-2, 2015. The focus is on the question of attribution, i.e., with what confidence can one say that a particular extreme event has been caused by global warming? Briefly, the scientific understanding thus far is that one can attribute specific heat waves to global warming with greater certitude than one can individual rainfall events, however extreme.
In July 2013, I wrote to James Hansen, one of the world’s pre-eminent climate scientists, to understand the linkage between extreme rainfall and global warming better. This wasn’t his area of specialisation, he modestly replied, but put me on to Tony Del Genio of the Goddard Institute at NASA, whose expertise Hansen rated very highly. Del Genio wrote back something worth quoting at length:
“One cannot attribute any single storm to climate change even if it sets the record for rainfall, for even if the climate were not changing, new records would occasionally be set. But if a pattern of more frequent extreme rain events is occurring, that might be the best evidence of climate change. Some scientists have argued that they are already seeing such changes.”
So is there such a pattern of extreme rain events in and around Chennai?
Finding the imprint of climate change
Chennai experienced exceptionally heavy rainfall in 1969, 1976, 1985, 1996, 1998, 2005 and now in 2015. The last four extreme rainfall events seem to have happened with slightly greater frequency than earlier, once in five years on average. Also relevant, all but the first of those dates fall within the current phase of global warming, which dates back to the mid-1970s. Worldwide, many impacts of global warming that we are currently witnessing date back to about 40 years ago, when the planet experienced a sudden spike in average global surface temperature. I’d wager that even a decadal frequency is higher than the occurrence of extreme rain events in the first half of the 20th century. What’s more, the last three of those years – 1998, 2005 and 2015 – each saw record average global temperatures. It’s likely that at least some of the last six extreme rain events in Chennai had the fingerprint of climate change.
There is also other, varied evidence that strengthens the argument that the ongoing deluge is a consequence of global warming. First, the year 2015 thus far has been and will almost certainly end up being the hottest year since instrumental records began in 1880. Second, a recent paper in Nature Communications by Mathew Roxy, Ritika Kapoor and others mentions a “rapid warming in the Indian Ocean” in recent years. Warmer sea surface waters are not a sufficient condition for very intense rains, but certainly help contribute to their intensity when they do occur. Third, the intense rains have been not just over Chennai but over a very wide region including catchments of the Adyar river, which has exacerbated the flooding in the city. And four, it seems to have stretched out unusually also in duration with a second bout of intense rains following the first a few days ago, and which has persisted for a number of days. So a measured answer to the question we started with – Is global warming responsible for the current deluge in Chennai? – would be: one still can’t say for certain, but it’s very, very likely.
Prakash Javadekar, the minister for Environment, Forests and Climate Change, doesn’t think so. Putting one’s head in the sand may be good policy for an ostrich, but not for a minister whose brief includes combatting and adapting to global warming. For this would be the third year in a row in which urban residents in some part of India have been hit by extreme rainfall events: Rishikesh and other towns of Uttarakhand in June 2013, Srinagar in September 2014, Mumbai (to a lesser degree than the others) in June 2015, and now Chennai. It’s also been three years in a row that each agricultural season, kharif and rabi, have been getting adversely affected by some manifestation or the other of climate change – untimely rains, droughts, or the most recent climate anomaly, intense rains accompanied by unusually large hailstones.
A report by the Centre for Science and Environment, Lived Anomaly, released last week, shows how this has become the new norm, and how its geographical spread is expanding: in March-April this year “no less than 15 states were hit and 18.23 million hectares of crops were damaged”. Even in the current deluge, much of the focus has been on Chennai city, but large swathes of agricultural land have also been inundated in northern Tamil Nadu and southern Andhra Pradesh. Instead of denying climate change or its effects, we need to operationalise policy to work on the assumption that increased frequency and deepening impacts are the new normal. That agriculture will get affected every single season; that towns in India will face a deluge from both the southwest and northeast monsoons; that multiple towns will be hit by climate change in the same season.
When climate change meets unequal growth
In every urban case mentioned above, the impacts of the deluge were intensified by rampant ‘development’. The Chennai-based environmental activist Nityanand Jayaraman has written feelingly of the wilful shrinking of the Pallikaranai marshlands, the erasure of a large network of water bodies in Chennai, the building of IT corridors and bypasses that have interfered with natural drainage flows. In Uttarakhand, it was the blasting of mountain sides for run-of-the-river projects and the dumping of the resulting waste into rivers, the reckless expansion of roads, etc., in a fragile ecosystem. In Mumbai in 2005, the ecological degradation of the Mithi River and urban growth choking the drainage system worsened impacts when 974 mm of rain fell in a single day.
Given the dual and combined reality of urbanisation and peri-urban expansions, and more regular and intensified climate change impacts, three issues then follow.
One, what needs to be done to ensure that natural hydrological flows are not hindered and that a repeat of Mumbai and Chennai does not happen? How does one minimise loss and damage, keeping in mind that in every urban impact of climate change, the costs are borne inordinately by the urban poor? In Chennai, too, it is they who will face the brunt of the health disaster that will follow in the floods’ wake.
Two, given that much reckless infrastructural expansion has already occurred in city after city, what of it can we undo? What of it can we not, but from which we can learn lessons for future urban expansion? After the 2005 floods in Mumbai, the municipal authorities there dredged the Mithi river, unblocked several kilometres of major nullahs, and desilted roadside gutters. But even so, it’s been tardy progress, with only a quarter of the work having been completed.
Three, we need to go deeper and interrogate the mindset that promotes this kind of reckless urban expansion, that valorises unequal and unsustainable growth, that pursues super-profits at the cost of everything else.
Ironically, the Chennai deluge has happened while negotiations are on in Paris about the planet’s climatic future. An overview last month by the World Resources Institute of many studies that examined all the 147 Intended Nationally Determined Contributions policy documents submitted by various nations suggests we are on course to a staggering 3 ºC of average warming above pre-industrial levels. If what’s unfolding in Chennai has happened at merely 1 ºC of warming – which we will touch this year – one shudders to think what 3º warming might imply for the residents of that great city, and beyond.
Nagraj Adve is a member of India Climate Justice. He works and writes on issues related to global warming.