Rapid heating of Indian Ocean worsening cyclones – scientists

    15 Jun 2021

    India’s cyclone season is being made more intense by the rapidly heating Indian Ocean, scientists have warned.

    Last week India was battered by Cyclone Tauktae, an unusually strong cyclone in the Arabian Sea, resulting in widespread disruption, The Guardian states.

    From May 12-19, in the midst of the devastating second wave of the pandemic, the powerful Cyclone Tauktae struck India’s west coast and killed more than 100 people, UN ESCAP reports. This was the deadliest cyclone in the Arabian Sea over the last decade.  Starting from southwestern Lakshadweep, the cyclone battered all states on India’s west coast and the remnants caused rainfall even in northern parts of India, Sindh province of Pakistan and Nepal. Its clouds advanced as far as China.

    Tauktae is a manifestation of climate change

    Climatologically, out of the five cyclones that form annually in the Bay of Bengal, only one develops in the Arabian Sea. But the risk scenario is rapidly changing.  A year ago, cyclone Amphan gathered energy from the anomalously high sea surface temperatures (SSTs) in the Bay of Bengal, intensified, and turned into a super cyclone in 24 hours. A week later, cyclone Nisarga formed over the Arabian Sea and struck the western coast of India. The western tropical Indian Ocean has been warming for more than a century, at a rate that is faster than any other region of the tropical oceans. It is now the largest contributor to the overall trend in the global mean SST. Tropical cyclones draw their energy from warm waters, which is why they form over warm pool regions where temperatures are above 28°C. The Arabian Sea, however, used to be cool, but at the time of the cyclogenesis process of Tauktae, the SSTs in the Arabian Sea were 30-31°C. Tauktae clearly demonstrates the relationship between global warming and the genesis of cyclones. 

    This week, another severe storm, Cyclone Yaas, formed in the Bay of Bengal, leading to more than a million people being evacuated into safe shelters.

    The Indian subcontinent has been facing the brunt of costly and deadly tropical cyclones for decades. But scientists say global heating is accelerating the rate of ocean warming, leading to an increased number of cyclones and rapid intensification of weak storms, with severe repercussions for the country.

    Cyclones are much more likely to gather intensity over warmer waters. The Arabian Sea, part of the west Indian Ocean, generally has a sea surface temperature of below 28C (82F), and recorded just 93 cyclones between 1891 and 2000. By comparison, the warmer Bay of Bengal in the east Indian Ocean, where temperatures are permanently above 28C, recorded 350 cyclones over the same period.

    Between 2001 and 2021, 28 cyclones formed in the Arabian Sea, along with a marked increase in storm intensity, fuelled by rising sea surface temperatures which reached as high as 31C (88F). A 2016 Nature study found anthropogenic global heating had contributed to the increased frequency of extremely severe cyclonic storms over the Arabian Sea.

    Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology, said: “The entire Indian Ocean is warming at a faster rate compared to the Atlantic or Pacific. And within the Indian Ocean, the western parts of the Indian Ocean are warming much more. We see that it [sea surface temperature rise] is connecting well with the changes in the intensity and frequency of cyclones especially in the Arabian Sea and also the rapid intensification.”

    The rapid intensification of weak storms into severe cyclones has been observed in the Arabian Sea and the Bay of Bengal over recent years. But the current forecasting models do not pick up rapid intensification in advance, posing a huge challenge to both disaster management authorities and the public in responding to the risk adequately, according to Koll.

    “Climate projections show that the Arabian Sea will continue to warm at a faster rate than what we have seen before, and there will be more extremely severe cyclones in the Arabian Sea,” he added.

    India is especially vulnerable as 14% of its 1.3 billion population live in coastal districts, and the number living in coastal areas below 10 meters elevation is forecast to rise threefold by 2060.

     “The trail of destruction left behind by Cyclone Tauktae is a grim reminder of India’s vulnerability to extreme climate events,” said Abinash Mohanty, program lead at the Indian thinktank Council on Energy, Environment, and Water.

    Mohanty said the government should invest in an improved emergency response framework that accounts for the compounded impacts of extreme events, a detailed climate risk assessment and climate-proofing of infrastructure.

    Inland countries such as Nepal can also be affected when strong Indian Ocean cyclones do not dissipate after landfall, causing excessive snowfall in the Himalayan highlands, said Arun Shrestha, a climate scientist at the International Centre for Integrated Mountain Development. “The blizzard in Everest of 1995, Cyclone Phailin in 2013, and Cyclone Hudhud in 2014 are some examples of cyclones impacting the Himalayas.”Anomalous warming in the Indian Ocean has also been linked to locust swarms, flooding in Africa, Australian bushfires, and changes in global rainfall patterns.

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