Natural Disasters

World Environment Day 2021: Why are cyclones intensifying in Indian Ocean

Explained: How Climate Change made Indian Ocean cyclones more intense and deadlier

 
Published: Saturday 05 June 2021

Climate change has made the Indian Ocean region more unpredictable than ever.

On the one hand, more cyclones are emerging; on the other, they are intensifying rapidly — gaining more power in a short time.

United States National Oceanic and Atmospheric Agency marks rapid intensification when wind speed of a storm increases by 55 kilometres per hour within 24 hours.

In the case of Cyclone Tauktae, the changes were indeed drastic: It turned from a depression into a cyclonic storm in about 48 hours. That was an anomaly. Depressions generally take four-five days to turn into full-blown cyclones.

The first Indian Ocean cyclone that rapidly intensified was Ockhi, which killed more than 200 people in Tamil Nadu and Kerala in November-December 2018. From a deep depression, it turned into a severe cyclonic storm in a matter of 24 hours.

To put this in context, a deep depression carries wind speed of around 50-60 kmph while a severe cyclonic storm can rage up to 117 kmph.

But the most blatant example of a cyclone flexing its muscles was Cyclone Amphan, which rapidly intensified from 140 kmph to 270 kmph in only 18 hours. This made it the most powerful cyclone in recorded history over Bay of Bengal. Similar rapid intensifications were witnessed with Cyclones Titli (2018) and Vayu (2019).

But why are cyclones intensifying so rapidly? The short answer is human-induced, or anthropogenic, climate change.

The World Meteorological Organisation (WMO) warned that average annual temperature rise could cross the 1.5 degrees Celsius threshold by 2026 — much, much earlier than predicted. Most of this heat is being absorbed by the oceans.

WMO’s State of Global Climate 2020 report says that 90 per cent of the heat accumulated on the planet has been absorbed by the oceans. Scientists have been able to record this heat across all ocean depths.

Worryingly, depths up to 2,000 meters have heated up rapidly. In 2019, this depth set a new heat record; preliminary observations pointed to 2020 being even hotter.

Why does all this matter? What are the links to the barrage of cyclones hitting India?

Cyclones and hurricanes are becoming more intense and more frequent because of this ocean heating. In 2018-19, the northern hemisphere had 72 tropical cyclones against the average of 59. They were also 4 per cent more powerful.

The southern hemisphere, where the Indian Ocean is located, experienced 27 cyclones, the highest since 2007-2008. Southern Indian Ocean had 18 cyclones, 13 of which reached hurricane levels. Northern Indian Ocean saw at least three cyclones carry wind speeds of 100 kmph or more — again a record.

The Arabian sea, which flanks India to the west, has seen a dramatic rise in cyclones. In 2019, five out of eight cyclones that hit the country emerged there.

The Government of India’s own reports shows that between 1993 and 2017, the sea level of the Indian Ocean rose by 3.3 millimeters annually. Therefore in the last 28 years, the sea level around the Indian peninsula has risen by nearly 9.5 centimeters.

Large swaths of India’s 7,500 odd kilometer-long coastline will be severely affected as the water levels rise. These are visuals from Cyclone Taukte. Cyclones will bring in more water both in the form of storm surges and rainfall which will lead to flooding, soil erosion, and displacement. 

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