Climate Change made Indian Ocean cyclones more intense and deadlier

Climate change has made the Indian Ocean more unpredictable than ever. On one hand, there are more cyclones emerging out of this ocean, and on the other hand, they are intensifying very rapidly, gaining more power in a very short time. This is called rapid intensification.

What is rapid intensification? Why is it so dangerous? And...What are its links to climate change? According to the US National Oceanic and Atmospheric Agency, rapid intensification happens when the wind speeds of a storm increase by 55 km/h within a period of 24 hours. In the case of Tauktae the changes were indeed drastic. It turned from a depression to a cyclonic storm in about 48 hours. This is an anomaly because generally, depressions take at least 4 to 5 days to turn into full-blown cyclones.

The first Indian Ocean cyclone which rapidly intensified was Okchi that killed over 200 people in Tamil Nadu and Kerala between November and 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 a wind speed of around 50-60 km/h while a severe cyclonic storm can rage up to 117 km/h.

But the most blatant example of a cyclone flexing its muscles was cyclone Amphan which rapidly intensified from a 140 km/h cyclone to 270 km/h in a matter of just 18 hours. This made it the most powerful cyclone in recorded history over the Bay of Bengal. Similar rapid intensification has also been witnessed with cyclones like Titli of 2018 and Vayu of 2019.

But why are cyclones intensifying so rapidly? The short answer is human-induced or anthropogenic climate change. The World Meteorological Organisation or WMO has already warned us that the average annual temperatures could cross the 1.5 degrees Celsius threshold by 2026, much... much...earlier than predicted. And most of this heat is being absorbed by the oceans. WMO’s State of Global Report 2020 says that 90% 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. But the worrying news has been that the ocean depths ranging from 0-2000 meters have heated up rapidly. The WMO report states that in 2019 this depth of 0-2000 meters set a new heat record and preliminary observations point that 2020 will be even hotter.

So why does all this matter? And 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% more powerful. The Southern Hemisphere where India is located experienced 27 cyclones, the highest since 2007-2008. The South Indian Ocean had 18 cyclones of which 13 reached hurricane levels. The North Indi an Ocean saw at least three cyclones carry wind speeds of 100 km/h or more which was again a record. And the Arabian sea which flanks India to the west has seen a dramatic rise in cyclones. In 2019, 5 out of the 8 cyclones that hit India emerged from the Arabian sea.

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.



Down to Earth is Science and Environment fortnightly published by the Society for Environmental Communication, New Delhi. We publish news and analysis on issues that deal with sustainable development, which we scan through the eyes of science and environment.