Frequent Marine Heatwaves in Indian Ocean: Study

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    In Context 

    • The study led by the Centre for Climate Change Research at the Indian Institute of Tropical Meteorology, Pune found that marine heatwaves (MHW) in the Indian Ocean are increasing in frequency.
      • This study is the first to have established a link between marine heatwaves in the Indian Ocean and changes in precipitation over the subcontinent. 

    Major Highlights 

    • Marine heatwaves
      • They are periods of extremely high temperatures in the ocean–above the 90th percentile. 
      • During an MHW, the average temperatures of the ocean surface (up to a depth of 300 feet) goes 5-7 degrees Celsius above normal
    • Causes: 
      • These marine heat waves occur due to background ocean warming in the Indian Ocean and also in response to El Niño events in the Pacific Ocean.
        •  Locally, a peak in solar radiation and a dip in evaporative cooling due to weak winds lead to the formation of these marine heatwaves.
    • Impacts: 
    • Western Indian Ocean and northern Bay of Bengal most affected
      • It found that the western Indian Ocean region generally experienced a higher increase in heat waves than the north Bay of Bengal.
      • The number of MHWs in the west Indian ocean increased by around 1.5 events per decade between 1982 and 2018. 

    Image Courtesy:DTE

    • The rise in marine heat waves (periods of extremely high temperatures in the ocean) over the Indian Ocean is leading to reduction in monsoon rainfall over Central India but an enhancement of monsoon rain over the South Peninsular region.
    • These events cause habitat destruction due to coral bleaching, seagrass destruction and loss of kelp forests, affecting the fisheries sector adversely. 
      • An underwater survey showed 85 percent of corals in the Gulf of Mannar near the Tamil Nadu coast got bleached after the marine heatwave in May 2020. 
      • A marine heat wave spanning over 6.5 million square kilometres had affected the Pacific Ocean off the coast of the state of Oregon in the United States in September 2019. 
    • Suggestions: 
    • The frequency, intensity and area covered by the marine heatwaves are increasing therefore we need to enhance our ocean observational arrays to monitor these events accurately in order to mitigate their impacts.
    • It is also imperative to update our weather models to skilfully predict the challenges presented by a warming world.

    What are Heat Waves ?

    • They are defined as prolonged episodes of extreme temperature over any region. 
      • Apart from temperature, humidity is an important parameter considered for declaring heat-related stress.
    • A Heat Wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India in the month of March to June. 
    • Factors: The possible factors responsible for Heat Waves include shifting of jet streams, El-Nino and La-Nina, anthropogenic factors like heat islands etc. 
    • Heatwave is considered if the maximum temperature of a station reaches: 
      • at least 40 degrees C or more for Plains 
      • at least 30 degrees C or more for Hilly regions. 
    • Categories of Heat Wave
      • Based on Departure from Normal 
      • Heat Wave: Departure from normal is 4.5 degrees C to 6.4 degrees C 
      • Severe Heat Wave: Departure from normal is >6.4 degrees C 
    • Based on Actual Maximum Temperature 
      • Heat Wave: When actual maximum temperature ≥ 45 degrees C 
      • Severe Heat Wave: When actual maximum temperature ≥47 degrees C 

    Source:DTE