A Spatial Shift of Heatwaves in India

• 12 Oct 2021

Why in News

Recently, a study has found a spatial shift of heatwaves in India, now occurring in new regions in the country.

• It also added that the eastern and western coasts, which are currently unaffected by heatwaves, wil be severely impacted in the future.
• It assessed the monthly, seasonal, decadal and long-term trends in heatwaves in the country from 1951-2016.

Key Points

• Findings:
  
  • A warming pattern was found over northwestern and southern India, while a progressive cooling phase over northeastern and southwest regions of the country.
  • A “spatio-temporal shift” is revealed in the occurrence of heatwave events, with a significantly increasing trend in three prominent heatwave prone regions- northwestern, central, and south-central India, with the highest being in west Madhya Pradesh (0.80 events/year).
    
    • Heatwaves have been traditionally associated with UP, Bihar, Delhi and northern parts of Madhya Pradesh.
  • Heatwaves were found in southern Madhya Pradesh, Andhra Pradesh, Karnataka and Tamil Nadu, where they would traditionally not take place.
    
    • Increases in heatwaves in Karnataka and Tamil Nadu are particularly significant, and point to increased events in the future.
  • A significant decrease in heatwaves over the eastern region, that is Gangetic West Bengal (−0.13 events/year).
  • An increasing trend of heatwave days and severe heatwave days was observed in the decade of 2001–2010 as compared to previous decades.
• Factors:
  
  • Two elements that have exacerbated the heatwave conditions in the country are the increase in night time temperatures, which disallows heat discharge at night, and increasing humidity levels.
• Heatwaves:
  
  • About:
    
    • A heatwave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western and South Central parts of India.
    • Heatwaves typically occur between March and June, and in some rare cases even extend till July.
    • India Meteorological Department (IMD) classifies heatwaves according to regions and their temperature ranges.
  • Criteria for Heatwaves:
    
    • The heatwave is considered when the maximum temperature of a station reaches at least 40°C for Plains and at least 30°C for Hilly regions.
    • If the normal maximum temperature of a station is less than or equal to 40°C, then an increase of 5°C to 6°C from the normal temperature is considered to be heat wave condition.
      
      • Further, an increase of 7°C or more from the normal temperature is considered a severe heat wave condition.
    • If the normal maximum temperature of a station is more than 40°C, then an increase of 4°C to 5°C from the normal temperature is considered to be heat wave condition. Further, an increase of 6°C or more is considered a severe heat wave condition.
    • Additionally, if the actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, a heat wave is declared.
  • Impact:
    
    • Heat Stress:
      
      • The presence of humidity in the environment prevents the thermoregulatory mechanism of evaporative cooling of the body through the process of perspiration, which can cause heat stress.
    • Increase in Heat-Related Mortality
      
      • An increase of 0.5 degrees Celsius in mean summer temperatures can cause an increase of heat-related mortality from 2.5 to 32%, and an increase in the duration of a heatwave from 6 to 8 days and result in an increase in the probability of mortality by 78%.
    • Heat Strokes:
      
      • The very high temperatures or humid conditions pose an elevated risk of heat stroke or heat exhaustion.
      • Older people avnd people with chronic illness such as heart disease, respiratory disease, and diabetes are more susceptible to heatstroke, as the body’s ability to regulate heat deteriorates with age.
    • Increased Energy Demands:
      
      • The sweltering heatwave also leads to rise in energy demand, especially electricity, leading to pushing up rates.
    • Lessens Workers’ Productivity:
      
      • Extreme heat also lessens worker productivity, especially among the more than 1 billion workers who are exposed to high heat on a regular basis.
      • These workers often report reduced work output due to heat stress.

Source: IE