High night-time temperature, humidity can hurt health, cause deaths’

NEW DELHI: High night-time temperatures have a huge impact on the health of people who don’t have access to cooling, according to an analysis by Gujarat-based Indian Institute of Public Health (IIPH) which helped in planning Ahmedabad’s heat response policy.

The analysis, based on average daily deaths in Ahmedabad between 2001 and 2016, concluded that all-cause mortality rates nearly doubled when the maximum temperature was above 45°C and the night-time temperature was also above 30°C , compared to when night-time temperatures remained between 28 to 30°C.

“This happens because the body doesn’t get rest. Normally, night is the time to recuperate from the impact of extreme heat, but if you do not get rest at night, then your body will be in overdrive. For example, if I ask someone to run and instead of giving rest intermittently, I say you can only slow to a brisk walk and then run again, the person will collapse. The same thing is happening when day and night temperatures are both extremely high,” said Dr Dileep Mavalankar, former director at IIPH Gandhinagar.

Dr Mavalankar said it was important to track all-cause mortality during the heatwave periods with data from the past to understand the excess mortality that may have been contributed by heat.

Delhi on Wednesday recorded a minimum temperature of 35.2°C — eight notches above normal and the highest minimum temperature for June since 1969, according to India Meteorological Department (IMD). This was also the sixth day on the trot that Delhi recorded a “warm night” — defined by IMD as when the maximum temperature is over 40°C, and the minimum is 4.5°C or more above normal.

Several other places over northwest India and east India have been recording warm to severe warm night conditions including Punjab, Haryana, West Uttar Pradesh and Bihar in May and June.

India is yet to release mortality figures from the current heat crisis.

Ahmedabad faced a heat wave in May 2010 when the temperature reached a high of 46.8 degrees C with a substantial increase in mortality. According to an IIPH paper published in March 2014 in Plos One, 4,462 all-cause deaths occurred in May 2010 (severe heat wave period), comprising an excess of 1,344 all-cause deaths. This was an estimated 43.1% increase over the 3,118 deaths in the reference period.

According to a paper published in Lancet Planetary Health in August 2022 titled: “The effects of night-time warming on mortality burden under future climate change scenarios: a modelling study,” the authors analysed a dataset comprising 28 cities across three countries (Japan, South Korea, and China), including 91,85,598 deaths. The time-series analyses showed the hot night excess was significantly associated with increased mortality risks, the relative mortality risk on days with hot nights could be 50% higher than on days with non-hot nights.

“During periods of hot days and nights, the body doesn’t get time to cool down and people often do not get sleep which increases the chances of a heat stroke. This is being seen now in people with no cooling systems at home and mostly among the elderly and babies. That is also because both these categories have poor temperature regulation mechanisms,” said Dr Sumit Ray, Critical Care Specialist and medical director, Holy Family Hospital.

Apart from hot nights, humidity also has a huge impact on mortality. “The mortality is likely to be more in areas with high humidity combined with high temperatures because of high heat index. So, states like West Bengal and Bihar may see higher impact, and hence they must monitor all-cause mortality on daily basis at least in big cities,” added Dr Mavalankar.

According to data compiled by IMD, between March 1 to June 9, the highest heat wave days have been recorded over Odisha (27) followed by Rajasthan (23), Gangetic West Bengal (21), Haryana (20), Chandigarh (20), Delhi (20) and West Uttar Pradesh (20).

According to scientists, even fit people will overheat and potentially die within 6 hours at wet bulb temperatures above 35°C.

A wet-bulb temperature (TW) of 35°C marks our upper physiological limit, and much lower values have serious health and productivity impacts, according to “the emergence of heat and humidity too severe for human tolerance,” a paper led by scientists from Jet Propulsion Laboratory/California Institute of Technology, USA, Department of Earth and Environmental Sciences, Columbia University. This is simply because evaporation of sweat is a cooling mechanism but at a wet bulb of around 35 degrees C, the human body can no longer cool itself by evaporating sweat, and exposure can lead to hyperthermia, an abnormally high body temperature.

The heat index gives a sense of what people may be experiencing because it combines relative humidity with the air temperature. On Wednesday, IMD’s heat index indicated that parts of northwest and east India were recording the ‘feels like’ temperature of 40 to 60 degrees C.

The burden is naturally disproportionately high on those living without access to cooling through day and night.

“We already know how hot nights can lead to a rise in deaths. Adaptation solutions are needed immediately for the most vulnerable so they have to be targeted and cooling solutions have to be provided to housing economically weaker sections. And by cooling we do not mean air conditioning. Telangana government has started its cool roof policy. We need more passive cooling measures in these houses, better ventilation etc. We need a response to extreme heat so that there is no loss of life,” said Abhiyant Tiwari, lead climate resilience and health consultant at NRDC India.

"People who are suffering the most are not well to do. But some elderly persons from homes with access to cooling are also reporting with symptoms of heat exhaustion. The recommendation to all would be to avoid heavy physical exertion during peak temperature hours. Avoid going out for a run in the sun, or even for a walk, do not work out in spaces without cooling. For those who have to work outdoors and do not have alternatives, they must also avoid peak afternoon hours and have access to safe, clean drinking water. But do they have a choice? We are seeing cases of acute gastroenteritis, severe dehydration and heat stress symptoms among people. This is possibly because they have developed a stomach infection also which has led to further dehydration,” Dr Ray at Holy Family Hospital explained.

“In cases of emergency, like those running high fever one can consider putting cool packs or towels in armpits, groin, forehead with tepid water and then let that water evaporate under the fan. But those having high fever, vomiting, and / or diarrhoea should seek medical help at a facility immediately,” Dr Ray cautioned.

“Millions in India endure extreme heat each day. They are exposed to the scorching sun; they do not have access to cooling devices; they see their land bake; their water dry up. They are the true victims of climate change. The irony is that they are not responsible for the greenhouse gas emissions that have caused the planet to heat up. The irony is also that the electricity that cools me and many others, will contribute to the stock of emissions and force the planet to further heat up,” said Sunita Narain, director general, Centre for Science and Environment.