Intense heatwaves linked to increased mortality rate: Report
What's the story
High-intensity heatwave days for long durations can significantly increase the mortality rates in Indian cities, a new study has shown, the Hindustan Times reported. The study—Impact of heatwaves on all-cause mortality in India: A comprehensive multi-city study—was published in the Environmental International journal this month. As part of the research, 10 cities, including Delhi, Mumbai, Chennai, Hyderabad, Bengaluru, and Kolkata, were analyzed to evaluate the direct impact of consecutive long-duration high-intensity heatwaves on mortality in urban areas.
Context
Why does this story matter?
In India, heatwaves usually occur from March to June, and occasionally, they may extend into July. Data from the India Meteorological Department (IMD) indicates that over the last decade, the intensity and duration of heatwaves have increased. Notably, extreme heatwaves were recorded in 2016, 2018, 2019, and 2023.
Data decoded
What does the study say?
The study discovered that when temperatures are unusually high for a day, exceeding those experienced on 97% of days in a year, there's a 12.2% rise in mortality rate. When high temperatures persist for two consecutive days, daily mortality increases by 14.7%. If this continues for three days, it rises to 17.8%, and if such high temperatures persist for five continuous days, daily mortality can increase up to 19.4%.
Correlation
Extreme heatwave conditions increase mortality rate by 33%
The study found that in cities like Ahmedabad, Chennai, Delhi, Hyderabad, Kolkata, and Varanasi, extreme heatwave conditions occur when temperatures exceed those experienced on 99% of days in a year. These conditions can lead to an increase in mortality rate of up to 33.3% when they persist for five consecutive days. According to the IMD, "A heatwave occurs when the maximum temperature reaches at least 40°Celsius or more for plains, and 37°Celsius or more for coastal station..."
168 heatwaves
3 heatwaves per year between 2008 and 2019
The study identified 168 heatwaves occurring between 2008 and 2019, indicating an average of three heatwaves per year across all cities. "Hyderabad and Pune had the highest average number of heatwaves, while Chennai and Varanasi had the lowest average at 2.2 each," the study said. "Delhi and Shimla exhibited the highest 'intensity' or percentage increase in temperature above the average of the daily mean temperature, with intensities of 3.0% and 3.8% respectively," it added.