NEW DELHI: The early heat waves of 2022 that began on March 11 have impacted 15 Indian states and Union territories as of now, according to data from the India Meteorological Department (IMD).
The data analysed by Down To Earth shows that Rajasthan and Madhya Pradesh have suffered the most among the states, with 25 heatwave and severe heatwave days each during this period.
The IMD says a heatwave happens when the temperature of a place crosses 40 degrees C in the plains, 37 degrees C in coastal areas, and 30 degrees C in the hills. The weather agency declares a heatwave when a place registers a temperature that is 4.5 to 6.4 degrees C more than the normal temperature for the region on that day. If the temperature is over 6.4 degrees C more than normal, the IMD declares a ‘severe’ heatwave.
The IMD also uses another criterion to declare a heatwave which is based on absolute recorded temperatures. If the temperature crosses the 45 degrees C mark, the Department declares a heatwave; when it crosses 47, a ‘severe’ heatwave is declared.
Surprisingly, after Rajasthan and Madhya Pradesh, the mountainous state of Himachal Pradesh has been the most affected by heat waves this year -- with 21 heat waves and severe heatwave days. One anomalous point in the IMD’s data is that the weather agency has officially declared only one heatwave day for Odisha.
D Sivananda Pai of the Kottayam-based Institute for Climate Change Studies says that anticyclones over western parts of Rajasthan in March and the absence of rain-bearing Western disturbances had triggered the early and extreme heatwaves. Anticyclones cause hot and dry weather by sinking winds around high-pressure systems in the atmosphere.
Raghu Murtugudde, a climate scientist at the University of Maryland explains that a north-south pressure pattern, associated with the La Nina phenomenon in the eastern and central Pacific Ocean that happens during winters in India, has persisted longer than expected and interacted with warm waves coming in from a rapidly warming Arctic region, leading to the heat waves.
In the first installment of the Sixth Assessment Report, the IPCC asserted that human activities have warmed the planet at a rate never seen before in the planet’s long history, and the Earth’s global surface temperature has warmed by 1.09 degrees C compared to the pre-industrial period of 1850-1900. Human influence is the main driver of hot weather extremes (which have become more frequent and intense since the 1950s).
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The IPCC report says that every additional 0.5 degrees C of warming will increase hot weather extremes, along with extreme precipitation and drought. Heat waves in India are likely to “last 25 times longer by 2036-2065” if carbon emissions remain high and push global temperature rise to 4oC by the end of the century, according to an international climate report published October 28, 2021, covering the G20 countries.
State-wise Number of heatwave days between March 11 and April 24:
Rajasthan -25, Madhya Pradesh -25, Himachal Pradesh -21, Gujarat -19, Jammu and Kashmir-16, Haryana-15, Delhi NCR-15, Uttar Pradesh -11, Jharkhand-11, Punjab-7, Maharashtra -6, Uttarakhand-4, Bihar -2, Goa-2, Odisha-1.