Heatwaves on the land are well known. But marine heatwaves — or the ones that form on oceans — have been on the rise in the waters around India, says a study.
Marine heatwaves are periods of extremely high temperatures in the ocean. These events are linked to coral bleaching, seagrass destruction, and loss of kelp forests, affecting the fisheries sector adversely. 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. The study appears in the journalJGR Oceans.
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 study notes.
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. “These changes are in response to the modulation of the monsoon winds by the heatwaves. This is the first time that a study has demonstrated a close link between marine heatwaves and atmospheric circulation and rainfall,” the authors note.
“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,” Roxy Mathew Koll, among the authors of the study and a scientist at the Indian Institute of Tropical Meteorology, Pune, said in a statement. “Since the frequency, intensity, and area covered by the marine heatwaves are increasing, we need to enhance our ocean observational arrays to monitor these events accurately, and update our weather models to skillfully predict the challenges presented by a warming world” he said.
Dr. Koll conducted the research in collaboration with other scientists — Saranya J.S. (Kerala Agriculture University), Panini Dasgupta (IITM), and Ajay Anand (Cochin University of Science and Technology).
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. Heatwaves killed 1,422 in Andhra Pradesh and 541 in Telangana in 2015 or about 90% of the national heat wave mortality of that year. 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.
