East India faced life-threatening heat stress in June, say experts

Parts of Bihar and West Bengal experienced continuous heatwaves for 19 and 17 days, respectively, in June, according to the India Meteorological Department

Large parts of eastern India saw a prolonged heatwave in June when experienced temperatures were high enough to be life threatening, experts said. Parts of Bihar and West Bengal experienced continuous heatwaves for 19 and 17 days, respectively, in June, according to the India Meteorological Department.

Bihar and West Bengal recorded a heat index of 50 to 60 degree Celsius during this period. (PTI)

Bihar recorded a heat index of 50 to 60 degree Celsius during this period. West Bengal would have seen similar values on the heat index as meteorological factors in both places such delayed monsoon and high humidity were similar. The conditions were deadly with the potential to kill thousands of vulnerable people, experts said.

Though the relatively lower number of heatwaves in April and May kept focus away from heat stress in the country, climate scientists said June’s extreme heat in eastern India should be taken as a warning. In June, Odisha, coastal Andhra Pradesh, Jharkhand and Chhattisgarh also recorded nine to 14 heatwave days.

“Bihar recorded a heat spell from May 30, which continued till June 22. Bhojpur district and the region around Arrah recorded the highest maximum temperature of 45.3-degree s. The heatwave pockets recorded maximum temperatures in the range of 40 to 45 degrees, with humidity ranging from 37% to 47%,” said Ananda Shankar, a scientist that the weather bureau’s Bihar office.

Maximum temperature of 40 degrees with 47% humidity translates to so-called “feels like” temperature or heat index of 53 degrees; a maximum temperature of 45 degree with humidity of 37% translates to a heat index of 60 degree, according to the US National Oceanic and Atmospheric Administration’s heat index calculator.

Total heatwave events this summer from March to June was 218 days over the country, the Met department said. It was the highest in the past 23 years after 2019, with 578 such days and 2022 with 455 days. Most heatwave days were reported in June, with parts of eastern India recording 11 to 19 heatwave days.

The combination of prolonged heat, high day temperatures and high humidity made it a heat stress disaster, experts said. “Other than the magnitude of heat and humidity, the duration of heatwaves is definitely a major factor in heatstroke related mortality,” said Roxy Mathew Koll, climate scientist at the Indian Institute of Tropical Meteorology. “Exposure is a major factor raising the risk and we often dismiss this while evaluating health and deaths.”

“There is no running away from heatwaves. Besides, the heatwave effect lasts for several days. The response of people is also not sharp, compared to the cyclones. People still decide to work outdoors in the farms or for construction. Ideally, they should stay indoors and keep themselves cool and hydrated,” Koll said. “We need to strengthen our heat action plans to sensitize people in terms of responding to heatwaves.”

It is often difficult to fix the number of deaths due to extreme heat, although public health experts have ways to extrapolate the number.

“There are two types of heat stroke which kill. One is direct or what is called exertional heat stroke. For example, a person is working in direct sunshine, he or she feels very hot, giddy and then dies due to a heat stroke . This is exertional heat stroke death. Such cases make up around 10% of heat related deaths. The other 90% of deaths are indirect heat stroke or nonexertional heat stroke,” said Dr Dileep Mavalankar, director at the Indian Institute of Public Health, Gandhinagar.

“A person becomes very hot dutng heat wave. hence the heart has to pump more blood to the skin to cool the body via sweat, which leads to heart failure in a older and comorbid person. If one is dehydrated, kidneys can start failing. When the core body temperature is very high more tha 40 deg C then the proteins will start failing which will then lead to failure of various organs like kidneys, brain, liver and heart. In such condition the body may be cold and clammy due to sweating to touch and hence detection may be difficult unless core body temperature is measured. Imagine someone living in a tin roof house on a very hot day, the temperature inside is pretty much like a furnace. Similarly, the core body temperature may be very high. But the immediate treatment should be cold water sponging or ice pack. In India rectal temperature is not measured everywhere but that is the only way to check core body temperature and establish the impact of heat,” he added.

As a result, doctors rarely attribute deaths directly to heat strokes as it is often an underlying cause. Hyperthermia can lead to impaired or heightened blood circulation and organ failure that then can cause death. “It’s impossible to say with certainty that heat caused deaths,” said Shankar.

Despite that, there are ways to roughly determine how many people died due to extreme heat. “First, we need to establish if there was excess mortality. For example, in Ahmedabad we observed the average daily mortality is 100 in May. During heatwaves we noticed excess mortality going up to 310 deaths which is 210 excess deaths. So, first it’s very important to track what is the mortality per 1,000 population and whether there are excess deaths. Even when there are no excess deaths, we should know what are the causes and track impact of heat,” said Dr Mavlankar.

Heatwaves have claimed more lives in India than other natural hazards, with the exception of tropical cyclones, the weather office said in a report in April. It used data from 1961-2020 to decipher heatwave climatology and occurrence.

On an average, more than two heatwave events occur over northern parts of the country and coastal Andhra Pradesh and Odisha. In some pockets, heatwave frequency exceeds four in a season. Most official weather stations show increasing trends of heatwave events during the 60-year period in terms of heatwave duration, frequency and severity.

The situation would only get worse. The frequency and intensity of warm days and nights are projected to increase over India in the next decades, while that of cold days and nights will decrease, a 2020 report by the earth sciences ministry said. The pre-monsoon season heatwave frequency, duration, intensity and areal coverage over India are projected to substantially increase this century, the report said.

The amount of water vapour in the atmosphere is expected to increase with global warming. The all India averaged annual and seasonal mean specific humidity and relative humidity are found to be increasing significantly for both gridded observations and reanalysis of datasets during the period 1979-2015, the ministry said. This translates into a higher heat index that the maximum temperatures indicate and would in many cases be potentially fatal to vulnerable sections of the population.