Oceans and seas are rising — millimetre by millimetre — the world over. Is India, with its extensive coastline and dense population, equipped to handle the impact of the phenomenon? While scientists struggle for accurate data, climate thinkers warn against a sluggish approach to solutions
The death of a rodent doesn’t always spark concern. But when the Australian government declared the extinction of the Bramble Cay melomys last February, the news created ripples.
For the species, endemic to the Great Barrier Reef, was killed chiefly by sea level rise (SLR). It was the second such casualty; the first, four years ago, was when five small islands, a part of the Solomon Islands in the west Pacific Ocean, sank and vanished from the face of the map.
The phenomenon of rising seas has been observed all over the world, including India, and its impact explored in a special report published by the United Nations’ Intergovernmental Panel on Climate Change (IPCC) last September. The global mean sea level (GMSL) isn’t just rising but accelerating, says the chapter on ‘Sea level rise and implications for low-lying islands, coasts and communities’.
Is India equipped to handle the dangers posed by SLR? The country’s coastline stretches 7,500-odd km and runs past nine states, including state capitals. The east coast, hemmed by the Bay of Bengal, is often pelted by cyclones, and the hitherto placid Arabian Sea on the west warmed up to brew four cyclones last year — a first in over a century. A fifth of India’s population lives along the coast; Mumbai, one of its biggest cities, thrusts into the Arabian Sea rather gingerly.
The oceans have risen consistently and, worryingly, it has risen faster in recent decades. According to the IPCC report, if the GMSL rise was 1.4mm a year from 1901 to 1990, it rose to 2.1mm a year in 1970-2015. The rise accelerated to 3.2mm a year between 1993 and 2015, and 3.6mm a year between 2006 and 2015.
The projections are for a dire future; the mean sea levels are expected to rise steadily, hitting around half a metre by 2100. Tiny islands and low-lying cities might experience, what scientists call, extreme sea levels by 2050.
Where does that leave Mumbai, a city shaped from the sea?
Water is the one element that defines — and wrecks — Mumbai. For a city that is home to an estimated 20 million people, Mumbai stands on shifty ground. Carved out of the Arabian Sea almost 200 years ago, the city was born when seven neighbouring islands were merged through engineering exercises into a single landmass. The prospect of the sea denting the land reclaimed from it is real for Mumbaikars.
Kapil Gupta, professor, department of civil engineering at the Indian Institute of Technology, Bombay, uses an analogy for the low-lying areas of the city — a bathtub. “We’ve filled up the low-lying areas with earth and later raised multistoreyed buildings on it, thereby reducing the holding capacity of those areas. When the water level rises, the bathtub will overflow,” says Gupta, one of the review editors of the chapter on ‘Sea level rise…’ in the IPCC report.
A large part of the city, Gupta notes, is just a notch above sea level. “In places such as Grant Road, even in summer during high tide, one can see water just a foot below the drains that empty into the sea.”
City residents can’t forget the floods of 2005, when Mumbai witnessed the worst deluge in its history. Relentless rain, coupled with storm surges and high tides, killed over 1,000 people. The city was flooded again in 2017. Recent studies have shown a three-fold increase in rainfall over the Western Ghats and central India.
Gupta introduces the prospect of SLR into this already volatile weather scene. When multiple factors — heavy rainfall, high tides and SLR — come in tandem, they spew disaster. “When it rains in coastal areas such as Mumbai or Kochi, and if tides are high during the time, water will not drain out immediately into the sea. In addition, if there is SLR, a few millimetres of water is enough to overflow and flood those living on the edge,” says Gupta.
SLR will impede the quick drainage of rainwater into the sea during times of high tide. “In the long term, it increases the chances of flooding for people living in low-lying areas, especially those living on the banks of rivers and drains emptying into the sea.”
While scientists agree that the sea levels are rising, the exact levels of that rise at different regions in the country need to be ascertained with greater accuracy. At the moment, Gupta says, we are dealing with global averages which definitely confirm SLR.
Tuhin Ghosh, one of the lead authors of the special report chapter, points out that data was the biggest hurdle when he tried to cull out numbers for SLR in India.
“There is a rise in sea levels in the Arabian Sea and Bay of Bengal coastlines. But to determine how badly it will impact us, we need estimates of the exact rate of rise. The range we have from India is too wide — anything between 3mm and 16mm,” adds Ghosh, an associate professor at the School of Oceanographic Studies, Jadavpur University, Kolkata. Scientists rely on exhaustive baseline data as well as advanced elevation data to arrive at projections, and India doesn’t have enough of either.
Ghosh emphasises the need for robust baseline data so that scientists and researchers in India will have something to bank on in the future. “Now we are trying to connect every kind of erosion with SLR. Erosion can be due to paucity of sediments or changes in hydrodynamic conditions. We have to consider all factors,” he adds.
To effectively measure SLR, scientists need both long- and short-term data, points out Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology, Pune. Scientists study long-term trends through tide gauges installed on the coast. “In some parts, for instance, at Colaba in Mumbai, we’ve had tide gauges for over 100 years. At the same time, at many other places, along the coast and open oceans, we do not have tide gauge networks. As a result, we don’t have enough data,” Koll explains.