Indian Heatwaves! What Are They, Why Are Some Parts Vulnerable, Why They Turned So Intense This Year, and More

The heatwave season, which began earlier than normal in March this year, turned rather unbearable for most parts of India throughout April. Though there seemed to be a respite in the first week of May, it was short-lived. Daytime temperatures remained over 45°C in many parts of Gujarat, Rajasthan, Haryana, Madhya Pradesh and Uttar Pradesh on Thursday, May 12.

Mercury levels have spiked sharply across northwest, west, and central India, including Delhi. These regions also logged two consecutive months — March and April — of hottest weather on record since 1901!

The temperatures during summers are typically high across these regions. Still, the magnitude of the spike in mercury levels has been causing concerns around the long-term health and safety of the residents, especially those most vulnerable to such prolonged heatwaves. Before we jump to details, let’s understand the basics.

What are heatwaves?

If you experience scorching temperatures accompanied by high humidity and profuse sweating, there are high chances that you may be witnessing a heatwave. But to be more precise, the India Meteorological Department (IMD) declares a heatwave if the actual temperatures over a region stay above 40°C and cross temperature thresholds of 4.5°C above average. If they stay over 6.4°C above average, it’s classified as a severe heatwave.

What causes heatwaves in Northwest India?

During the summer months, the highlands in north India prevent the incursion of any cold air from the higher latitudes. Therefore, dusty, hot and dry winds blow over the northwestern region and the Indo-Gangetic Plains, making these regions vulnerable to frequent heatwaves. Such desert summer winds are known as Loo in the region and are often the cause of fatal heatstrokes.

Moreover, there are anticyclones developing over north India as well as the Iran-Afghanistan-Pakistan-Tibet belt starting in March every year. These are the areas of high atmospheric pressure where the air sinks, causing hot and dry weather. These systems also result in high temperatures over parts of western India in March.

The arrival of monsoons in late June is the only assured respite for the region from these deadly heatwaves.

Did lack of Western Disturbances lead to persistent and intense heat waves this year?

In North India, the summer rains are dependent on the Western Disturbances. These extra-tropical systems originate in the Caspian and the Red Sea and traverse over Iran, Afghanistan and Pakistan to reach India. Usually, while flowing, these systems carry moisture from the sea and are associated with rainfall, snowfall and fog in Northern India.

The absence of this periodic rainfall is believed to have led to a dire situation this year! The IMD’s director-general Mrutyunjay Mohapatra explains, “If the WDs move across southern latitude, it gets moisture from the Arabian Sea, which in turn leads to rainfall activity over northwest India. If it does not, its impact will be dry”.

Although were six WDs in April, most of them were feeble and dry and moved across the higher ridges of the Himalayas. “Only last three systems caused gusty winds and dust rising winds and dry thunderstorms at several places, including Delhi NCR, and also dust storms over Rajasthan on April 14, 22 and 25,” Mohapatra explained.

Because of these dry WDs, this April has become the hottest month for Northwest and central India in the last 122 years.

What other factors led to intense heat waves this year?

Other factors which may have led to unbearably hot weather conditions throughout the country are as follows:

Prolonged La Niña: According to Raghu Murtugudde, a climate scientist at the University of Maryland, prolonged La Niña could also have played a role. La Niña patterns over the eastern and central Pacific Ocean usually prevail during winters in India but have persisted longer than expected this year. The north-south pressure pattern associated with the phenomenon and interacted with warm waves coming in from a rapidly warming Arctic region, leading to the heat waves in most of India that could continue until June, explains Murtugudde.

Climate change: According to recent IPCC reports and statements given by experts, the number of heatwaves this year could be a direct response to global warming. Estimates suggest that such intense heatwaves would have happened only once in every 50 years. However, due to climate change, they are now expected to occur once every four years. The World Meteorological Organisation (WMO), on the other hand, says that “it is premature to attribute the extreme heat in India and Pakistan solely to climate change.”

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