Focus on warming seas to guide cyclone forecast - Hindustan Times

Focus on warming seas to guide cyclone forecast

Jun 13, 2023 09:36 PM IST

With Cyclone Biparjoy barrelling up the Arabian Sea off India’s western coast, why is the Arabian Sea so warm this spring?

Cyclone Biparjoy is barrelling up the Arabian Sea off India’s western coast. The extremely severe cyclone rapidly gained strength in two 24-hour periods over the past seven days, with winds gusting up to 150 km/h. With global warming, and especially the upper ocean heating up — where oceans absorb excess heat trapped in the atmosphere due to the climate crisis — cyclones are moving slower and lasting longer. The rapid warming of the northern Arabian Sea, where sea-surface temperatures have risen rapidly in the last four decades, has produced more extreme rainfall events during the monsoon season over northwest India and Pakistan. During the pre-monsoon season, the frequency of cyclones over the Arabian Sea has been increasing, and they are occurring closer to the monsoon’s onset, arguably due to remote influences from the Arctic. This time, Biparjoy is persisting well past the monsoon’s onset.

Cyclone Biparjoy is barrelling up the Arabian Sea off India’s western coast(PTI) PREMIUM
Cyclone Biparjoy is barrelling up the Arabian Sea off India’s western coast(PTI)

Why is the Arabian Sea so warm this spring? It is well known that the Indian Ocean sees a confluence of additional heat from the Pacific through the Indonesian Seas as well as through the direct pipeline from the Southern Ocean. The Arabian Sea is seeing additional warming contributions through the atmosphere from the Arctic and North Atlantic during the winter, and from the northwestern Pacific during the spring. The largest land warming occurring over West Asia into the Mediterranean (between 1.5 degrees and 2 degrees Celsius above long-period average) is likely adding to this. The temperature anomalies for April and the average warming from January to April clearly show that the Arabian Sea is much warmer than normal this year. Surface temperature anomalies for April 2023 as departures from a long-period average highlight the cooling over India (between 0.5 and 1 degree Celsius) and the warming over Western Asia into the Mediterranean as well as the Arabian sea (between 1 and 1.5 degree Celsius).

The significance of the Arabian Sea warming becomes clearer when we consider the percentiles of the temperature anomalies. Temperature percentiles for April 2023 show that the entire Arabian Sea and the tropical Indian Ocean were much warmer than the long-period average.

From January to April this year, average temperature percentiles underscore the unique local and remote forces that kept the Arabian Sea well above normal temperatures. We now need to watch Biparjoy for the so-called rapid intensification, where winds within a cyclone can accelerate by more than 55 km/h within just 24 hours. Two of these episodes have happened already.

Lest we presume that the Arabian Sea is warming purely due to global warming, we should not forget that natural variability is a key player in locally adding to or subtracting from global warming impacts. The key factor here is the transition from the La Niña winter of 2022-23 to the upcoming El Niño summer of 2023-24. The monsoon tends to experience its largest deficit of around 15% during such a transition from a La Niña winter to an El Niño summer. But alas, even a drier monsoon will not spare northwestern India and Pakistan from extreme rain. The soaking from Biparjoy and the wet soils may leave the region much more vulnerable to additional monsoon extremes to follow. It is very critical, therefore, to be prepared for extreme events in the coming months.

The good news in this wild swing of the climate hammer is that India’s investments in weather and climate forecasting have led to greatly improved cyclone forecasts as well as forecasts at short (days 1-3), medium (days 3-10), and extended (weeks 2-4) range, comprising the so-called ready-set-go forecast system. A seasonal or an extended range forecast can help disaster management agencies to “ready” the system with allocations of resources and personnel. Medium-range forecasts allow the “set” step to go into action by moving the equipment into place, readying shelters, food, water, and warning people, while also preparing the health care system. Short-term forecasts set in motion the “go” step to save lives and property. So even as India utilises its expertise in natural disaster management, future forecasts would do well to keep an eye on the unusually warming Arabian Sea, and the unpredictable consequences when the climate crisis combines with local factors.

Raghu Murtugudde is visiting professor, IIT-Bombay and emeritus professor, University of Maryland The views expressed are personal

Catch every big hit, every wicket with Crickit, a one stop destination for Live Scores, Match Stats, Infographics & much more. Explore now!

See more

Get Current Updates on India News, Elections 2024, Lok sabha election 2024 voting live , Karnataka election 2024 live in Bengaluru , Election 2024 Date along with Latest News and Top Headlines from India and around the world.

Continue reading with HT Premium Subscription

Daily E Paper I Premium Articles I Brunch E Magazine I Daily Infographics
Share this article
Story Saved
Live Score
Saved Articles
My Reads
Sign out
New Delhi 0C
Thursday, July 18, 2024
Start 14 Days Free Trial Subscribe Now
Follow Us On