Severe heatwave in India: What makes this heatwave unusual? Causes, duration explained

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Published: May 28, 2020 1:57 PM

Heatwave, in its first spell this year, has affected five states and has caused severe to very severe conditions making the summer of 2020 somewhat unusual than it really is.

A heatwave can occur when there is a jump of 4-5 degrees from its normal temperature (maximum) over an area.

Severe heatwave in India: It has been five days since the mercury within the thermometers has been on the rise in the country. Heatwave, in its first spell this year, has affected five states and has caused severe to very severe conditions making the summer of 2020 somewhat unusual than it really is. Temperatures have reached as high as 50 degree celsius causing distress in states like Rajasthan, Maharashtra, Madhya Pradesh, Uttar Pradesh and Delhi. But many fail to understand why such a sudden spike in temperatures after a few days of rain. In order to comprehend the phenomenon, it is necessary to first understand what exactly a heatwave is.

What is a heatwave and how long can it last?

A heatwave can occur when there is a jump of 4-5 degrees from its normal temperature (maximum) over an area. Some meteorologists declare a heat wave when temperature climbs above 40 degree celsius, the IE reported. According to the report, if the area reports a maximum temperature above 45 degree celsius, a severe heatwave condition is declared. India Meteorological Department (IMD) has informed that in order to declare a heatwave, the criteria should be met by minimum of two stations in a Meteorological subdivision, that too, for two consecutive days.

After the data is assessed, heatwave is announced on the second day. The IE report highlighted that a heatwave can last for four days and in some cases it can also go up to seven days and ten days in worst cases. Currently, after four days of heatwaves, IMD has declared that it will recede from today and going forward, the temperatures are likely to declined in northern and central parts of the country.

Will heatwaves impact the entire country at once?

Since the heatwaves are common in some places, the IMD has categories as the Core Heatwave Zone (CHZ). Usually, these zones experience more than six heatwaves in a year, the report said. It further added that extreme parts of India- extreme north, northeast and southern parts are less prone to have heatwaves.

Why did the heatwaves come in May third week this year?

Usually in India, when summer season peaks by May 15, the temperature across these CHZs cross above 40 degrees and remain till around 45 degrees. The temperature did not rise till May 21 this year, making the summers quite unusual. According to the IE report, Western Disturbances (also known as cyclonic movements in Mediterranean sea impacting air flow or eastward moving winds) kept influencing India’s weather patterns till late April. This year, Western Disturbances received support from the easterly winds that were blowing over the Bay of Bengal, which kept the temperature cooler than usual till early May. It has been highlighted that there have been around 20 Western Disturbances between January and March this year.

Did cyclone Amphan contribute to the heatwave?

After the tyranny of cyclone Amphan ended, a sudden rise in temperature across the central and northern plains in India has been noted. Citing a confirmation from experts, the report said that the cyclone was successful in dragging the maximum moisture from the South Peninsula, Bay of Bengal and some parts of central India. This has triggered dry north-westerly winds to pass via some Indian states thus, leading to severe heatwave.

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