Marine Heatwaves (MHWs)

Context

Increasing heatwaves, caused by global warming, played a key role in turning Cyclone Amphan into a super cyclone.

Super Cyclone, Amphan

· Amphan was the first super cyclone in the Bay of Bengal in the last 21 years.
· It was also the costliest tropical cyclone on record in the North Indian Ocean, with reported economic losses of approximately $14 billion in India.
· Warmer Surface Water may have helped sustain marine heatwaves.
· Marine heatwaves are likely to have helped intensify the cyclone from Category 1 (cyclonic storm) to Category 5 (super cyclone) in less than 36 hours.

About Marine Heatwaves

Marine Heatwaves can be understood as discrete periods of extreme regional ocean warming.
They can last for weeks or even years.

Reason behind the phenomenon

Due to global warming, the tropical Indian Ocean, at the surface, is warming at a faster rate as compared to the rest of the global ocean.
The high sea surface temperatures are more susceptible to generating extreme temperature conditions.
The marine heatwaves in the western Indian Ocean and the Bay of Bengal are the “ocean’s erratic responseto increased warming of waters.”
They appear in the form of periods of extremely high temperatures in the ocean and are causing drying conditions over the central Indian subcontinent.
Anthropogenically-driven climate change is causing ocean warming globally, and regionally MHWs are driven by unusual weather patterns and disruptions in ocean currents and mixing.

Why is the Bay of Bengal more prone to tropical cyclones?

The Bay of Bengal is a more active basin than the Arabian Sea in terms of frequency and intensity of cyclones.
The Bay of Bengal exhibits high sea surface temperatures (about 28°C) throughout the year and is more prone to tropical cyclones.
The Bay of Bengal is home to about 5-7% of the total number of tropical cyclones occurring globally each year and this makes the North Indian Ocean vulnerable to the highest number of fatalities globally.