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Heat wave - Reasons UPSC NOTE


Heat wave - Reasons

Climate change:

  • Climate change is increasing both the frequency and the intensity of extreme weather events.

  • Normal monsoon patterns have given way to, among others, delayed onset, short but intense bursts of rain, and delayed withdrawal.

  • Some weather events have also become drier and others wetter thanks to the effects of climate change on the water cycle, which leads to more evaporation and eventually causes more precipitation.

  • Some areas also experience heavier than normal precipitation while others are becoming prone to unexpected droughts.

  • The U.N. Intergovernmental Panel on Climate Change’s Sixth Assessment Report warned of prolonged rain-free periods along with excessive rainfall in many parts of the world. 

  • In recent decades, India has recorded several such extreme events.

  • From June to September 2022, there were variations in rainfall in different parts of India: 

  • A significant increase was recorded in central and south India whereas parts of Kerala, Karnataka, and Madhya Pradesh flooded many times. 

  • A significant shortfall was also recorded in many parts of Uttar Pradesh, Bihar, Odisha, and the northeast.

  • High monsoon rainfall variability and continuous warming raise the probability of dry and hot extremes.

  • There is also a strong connection between land and ocean heatwaves, driven by atmospheric circulation, increase in sea-surface temperature, and feedback mechanisms that exacerbate the intensity and duration of extreme temperatures.

  • For example, when a land-based heatwave occurs, it can enhance evaporation rates and reduce soil moisture, leading to drier conditions.

  • This drier surface, in turn, absorbs more solar radiation, amplifying the heatwave. 

  • This feedback can also influence the persistence of heatwaves over both land and ocean environments.

Marine heatwaves:

  • The oceans play a key role in the formation of monsoon winds and in keeping the monsoon alive. 

  • When extreme heat warms their waters, the change in temperature can lead to cascading effects, such as marine heatwaves, ocean acidification, sea-level rise, and ice melting faster at the poles.

  • Marine heatwaves are periods of temperature much higher than the average seasonal temperature in that region. 

  • The Indian Ocean recorded six marine heatwaves over a period of 52 days in 2021. 

  • They used to be rare in this water-body but today are an annual occurrence.

  • A low pressure develops over the Indian subcontinent when the land heats up during the summer. 

  • The moisture for monsoon rains is thus carried by the winds as they blow in from the Indian Ocean.

  • However, rainfall over the land decreases when ocean heatwaves occur, as the winds are drawn to areas over the ocean instead of land.

  • In 2022, IITM researchers reported a significant increase in the number of marine heatwaves in recent decades because of warming and a strong El Niño (a phenomenon that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean).

  • Specifically, they found that from 1982 to 2018, the western Indian Ocean region had a four-fold increase in marine heatwaves (an increase of 1.2 to 1.5 events per decade); 

  • The northern Bay of Bengal region followed with a two- or three-fold rise (an increase of 0.4 to 0.5 events per decade).



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Heat wave - Reasons UPSC NOTE
Heat wave - Reasons UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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