Explained | What is causing the intense heat in north, west, central and east India? 

A man cools off from tap water during a hot summer day, on the outskirts of Jammu on April 30, 2022. | Photo Credit: PTI

The story so far: India is in the throes of an unusually long series of heatwaves that began in the end of March and scorched north India for most of April. The India Meteorological Department (IMD) said April was the hottest in northwest India in 122 years. It has also been an unusually hot April– with temperatures touching above 40 degree Celsius – in large parts of Bihar, Jharkhand and West Bengal.

How widespread is the heatwave?

Records from IMD suggest that the average maximum temperature till April 27 was 35.7 degree Celsius, the highest in five years for this month. In Madhya Pradesh, Rajasthan, Punjab, and Gujarat, the average maximum temperature in April 2022 so far has been the highest since 1951; while it has been the second highest in Delhi, Uttar Pradesh, and Haryana. In most of these States, the temperature has been consistently above 42 degree Celsius and around 5-6 degrees above normal for this time of the year.

Latest IMD forecasts say heat wave conditions prevail in many parts of Punjab, northwest Rajasthan and Vidarbha, Maharashtra. It’s also unusually hot in parts of Himachal Pradesh, west Madhya Pradesh, Jharkhand, Bihar, Gangetic West Bengal and Odisha. Maximum temperatures were 43-46 degree Celsius over most parts of Rajasthan, Vidarbha, Madhya Pradesh and east Uttar Pradesh, in many parts of Gujarat and interior Odisha; in some parts of Madhya Maharashtra and in isolated pockets of Bihar, Jharkhand, interior Gangetic West Bengal and 40-43 degree Celsius over most parts of Haryana-Delhi, Punjab and in isolated pockets of west Uttar Pradesh, Chhattisgarh, Marathwada, Telangana and Rayalaseema.

Workers use their helmets to pour water to cool themselves off near a construction site on a hot summer day on the outskirts of Ahmedabad, Gujarat, on April 30, 2022.

Workers use their helmets to pour water to cool themselves off near a construction site on a hot summer day on the outskirts of Ahmedabad, Gujarat, on April 30, 2022. | Photo Credit: Reuters

These scorching conditions are expected to continue until the middle of next week until, the agency says, a western disturbance from West Asia brings rain to parts of north and north-western India. While it is not unusual for the latter half of April to be dry and hot in most of north, west and central India, this year is unusual in that this follows the warmest March in 121 years with the maximum temperature across the country nearly 1.86 degree Celsius above normal.

How are heatwaves defined?

A heatwave is declared when the maximum temperature is over 40 degree Celsius and at least 4.5 notches above normal. A severe heatwave is declared if the departure from normal temperature is more than 6.4 degrees, according to the IMD. Based on absolute recorded temperatures, a heatwave is declared when an area logs a maximum temperature of 45 degree Celsius. A severe heatwave is declared if the maximum temperature crosses 47 degrees.

A kid jumps into the Gomti river in Lucknow, Uttar Pradesh, on a hot summer afternoon on April 05, 2022.

A kid jumps into the Gomti river in Lucknow, Uttar Pradesh, on a hot summer afternoon on April 05, 2022. | Photo Credit: SANDEEP SAXENA

Is climate change responsible?

The heat-trapping consequences of global warming imply that climate extremes such as heatwaves are expected to rise in frequency. Instances of extreme rainfall, as well as longer rainless spells are expected, according to assessments by the Intergovernmental Panel on Climate Change.

The main reason for the scorching heat in the northern parts of the country is lack of rainfall. Usually, periods of high temperature are punctuated by periodic episodes of rain but this was largely absent during March and April. Ironically, April also saw maximum instances of extreme rainfall since 2018 though it was concentrated in the south and north-eastern India. The rain-bearing western disturbances originate because of temperature gradients between the northernmost parts of the globe and the latitudes passing through West Asia. Weaker gradients mean weaker rains. This March and April, cooler than normal conditions in the Pacific Ocean failed to aid rainfall in north India.

Watch | What is causing the intense heat in India?

What impact do heatwaves have over India?

Research through the years shows that the number of heatwave days in India is increasing every decade. From 413 in 1981-90 to 575 in 2001-10 and 600 in 2011-20, the number of days that see extremely hot days is persistently increasing at 103 weather stations. Some parts along eastern India, such as Andhra Pradesh, Telangana and Odisha, also register higher humidity along with high temperatures, leading to a rise in a condition called ‘wet bulb’ temperature, that at its mildest can cause extreme discomfort and at its worst cause dehydration and death.

Heatwaves have killed more than 17,000 people in 50 years in India, according to a research study by IMD scientists. However, the intensity and length of heatwaves don’t have a direct connection to India’s monsoon that sets in over Kerala in June.

What is being done to buffer against high temperatures?

Over the years, forecast systems have improved that allow heatwave warnings to be disseminated via electronic channels and phones instantaneously. Many State governments across the country have declared school holidays; some have highlighted the dangers of working outdoors during the day. Many State governments award monetary compensation for deaths linked to heatwaves.

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Printable version | May 5, 2022 11:30:09 am | https://www.thehindu.com/sci-tech/energy-and-environment/explained-what-is-causing-the-intense-heat-in-north-west-central-and-east-india/article65369867.ece