Environment

The heat is on: savage signs of climate change speeding up

According to a 2021 paper in Weather and Climate Extremes, as many as 17,362 persons died between 1970 and 2019 in India due to heatwave.

According to a 2021 paper in Weather and Climate Extremes, as many as 17,362 persons died between 1970 and 2019 in India due to heatwave. | Photo Credit: Mohd. Arif

The Indian Meteorological Department (IMD), established in 1875, began by tracking temperature, moisture and rain. Now it is one of the biggest operations in the world that tracks dozens of weather parameters. This information is shared in the public domain.

When the IMD came into being, its goal was to “Study systematically the climate and weather in India as a whole and application of the knowledge thus acquired to the issue of storm and other warnings and daily forecasts.”

In the aftermath of a disastrous famine in 1877, the department was tasked with forecasting south-west monsoon. Now, as all signs point to climate change, should the IMD factor in microclimate conditions to save lives?

The IMD factors long term data between 1981-2010 for normal temperature per day and predicts heatwave conditions accordingly, and issues warnings if the temperature is expected to cross 40 degree Celsius in the plains, or 30 degree Celsius in hilly areas. For coastal regions, it does so when the maximum temperature is expected to be higher than 4.5 degree C or the maximum temperature is above 37 degree C. But these conditions have to be met at two stations at a sub-division of the IMD. A heatwave is declared on the second day.

‘Heat deaths’

According to a 2021 paper in Weather and Climate Extremes, as many as 17,362 persons died between 1970 and 2019 in India due to heatwave and in 2015 alone, the figure was nearly 2,000. Every year, hundreds of people die due to heatwave conditions in the country according to the National Crime Records Bureau data.

In 2020, the lowest number of 530 deaths were recorded, possibly due to COVID-19 lockdown and restrictions on work that year. A large number of these deaths go unrecorded as a heatwave is not a notified disaster.

Temperature and discomfort

The real feel of temperature varies from place to place. Chennai becomes cool in the evening but hours before that, it is oppressively hot. Hyderabad cools down late in the evening but the discomfort level is nowhere near that of Mumbai, Chennai, Visakhapatnam or other coastal places.

While the coastal cities log temperatures near 30 degree Celsius, many places in the plains log temperatures near 40 degree Celsius during peak summer. Why do places with lower temperature feel hotter? The difference is the ambient humidity, which affects how the body sweats.

How does temperature influence body?

The human body temperature (36.1 to 37.8 degree C) is regulated by the hypothalamus which manages production and loss of heat. The body loses heat by radiation, convection, conduction and evaporation of sweat. Conduction, radiation and convection require a temperature differential between the skin and environment while evaporation requires water vapour pressure differential. When the surrounding temperature is higher than the body temperature, the only way the body can cool down is by sweating (evaporation). Any condition that hampers evaporation can be life-threatening. High relative humidity, reduced cardiac output, air circulation (lack of breeze, tight clothes), could result in an abnormal rise of body temperature that can culminate in life-threatening heatstroke.

Heat stress and joblessness

According to International Labour Organisation (ILO), India has been the worst victim of heat stress with the loss of 4.3% working hours in 1995. It is projected to lose 5.8% of working hours by 2030. This may trigger further job losses. “Because of its large population, India is, in absolute terms, expected to lose the equivalent of 34 million full-time jobs in 2030 as a result of heat stress. Although most of the impact in India will be felt in the agricultural sector, more and more working hours are expected to be lost in the construction sector, where heat stress affects both male and female workers,” noted a 2019 ILO paper on working on a warmer planet.

One of the factors why India is among the countries bracketed as most vulnerable to productivity losses is that a large number of people are employed in agricultural and/or construction sector.

Tracking heat stress

There are two methods which measure the impact of heat on human body better than just recording temperature.

The first one is the Heat Stress Index, which factors in the role of temperature, humidity and sunlight on human body. It measures how hot it feels when high humidity is combined with temperature, air circulation and radiant heat.

The second is the Wet Bulb Globe Temperature (WBGT). This measure is still in the prototype stage but factors in heat stress approximating working conditions. It measures temperature in direct sunlight, factoring in wind speed and humidity (key for normal sweating) angle of the sun and cloud cover.

What’s next?

India is among the countries expected to have high WBGT values. Many countries in the Middle East, which experience high day temperatures during summer, mandatorily declare a work break. A three-month mid-day break begins at 12.30 p.m. and ends at 3 p.m. in the UAE. Other countries with similarly high day temperatures also have a provision for work breaks.

April and May have been some of the hottest days on record in India. Working conditions in India have to be revised quickly to factor in the hotter days. The National Disaster Management Authority (NDMA) had called for revised guidelines for heatwave alerts that should be region-specific. For workers and employers, the NDMA has these guidelines: “Schedule strenuous tasks to cooler times of the day. Increase the frequency and length of rest breaks for outdoor activities”.


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Printable version | May 23, 2022 6:56:35 pm | https://www.thehindu.com/sci-tech/energy-and-environment/the-heat-is-on-savage-signs-of-climate-change-speeding-up/article65413291.ece