Marine Heatwaves rising around India

What is a Marine Heatwave ?

Marine heatwaves are periods of “extremely high temperatures” in the ocean.
Marine heatwaves can occur in summer or winter and they are defined based on differences with expected temperatures for the location and time of year.
These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely.
The most common drivers of marine heatwaves include ocean currents, Winds and climate models like El-Nino.
Marine heat waves affect ecosystem structure and drastically affect the Biodiversity.
Eg: In 2016, marine heatwaves across northern Australia led to severe bleaching of the Great Barrier Reef and have been speculated to be linked to mangrove die-offs in the Gulf of Carpentaria.

Why in news?

An underwater survey showed that 85% of the corals in the Gulf of Mannar near the Tamil Nadu coast got bleached after the marine heatwave in May 2020.
Emerging studies have reported their occurrence and impacts in the global oceans, but are little understood in the tropical Indian Ocean.

News in detail

The study shows that the Western Indian Ocean region experienced the largest increase in marine heatwaves at a rate of about 1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.5 events per decade.
From 1982 to 2018, the Western Indian Ocean had a total of 66 events, while the Bay of Bengal had 94 events.
The marine heatwaves in the Western Indian Ocean and the Bay of Bengal increased drying conditions over the central Indian subcontinent correspondingly, there is a significant increase in the rainfall over south peninsular India in response to the heatwaves in the north Bay of Bengal.
This is the first time that a study has demonstrated a close link between marine heatwaves and atmospheric circulation and rainfall.
Climate model projections suggest further warming of the Indian Ocean in the future, which will very likely intensify the marine heatwaves and their impact on the monsoon rainfall.
Typically, heatwaves on land are associated with the north and northwest of India and over coastal Andhra Pradesh, north Odisha and parts of West Bengal.
Thus, there’s been an increase in the number of affected regions in recent years, with more parts of the Himalayan plains, regions north of Andhra Pradesh and Central India also registering more heatwaves.

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